Abstracts of some papers by John M.C. Hutchinson


I now work in the Malacology Department in the Senckenberg Museum für Naturkunde Görlitz.

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Privat, Dr J.M.C. Hutchinson, Senckenberg Museum für Naturkunde Görlitz, Am Museum 1, 02826 Görlitz, GERMANY



 

J.M.C. Hutchinson, 1989. Control of gastropod shell shape; the role of the preceding whorl. Journal of Theoretical Biology 140:431–444.

I propose that a snail uses the shape of the preceding whorl as a cue to dictate where upon it the new whorl attaches. The consequent constant difference in orientation between successive whorls can generate the domed outline that is commonly observed. This "road-holding" model is considered more representative of growth processes than models that generate logarithmic helicospirals, but I consider how the curve of the shell just behind the aperture might also act as a cue, to line up the shell-secreting mantle. I discuss why it might be that shells dome less as they grow, and suggest a set of biologically more meaningful measurements with which to compare shells.
doi link from Science Direct
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J.M.C. Hutchinson, 1990. Stabilising selection in Weldon’s snails: a reappraisal. Heredity 64:113–120.

This paper reconsiders Weldon’s (1901, 1904) and Di Cesnola’s (1907) oft-quoted research on stabilising selection on shell shape of terrestrial snails. Although I recognise problems in the experimental design, the commonest criticism is probably inapplicable. The statistical analyses were flawed, but a crude reanalysis supports Di Cesnola’s conclusions, whilst Weldon’s results are also suggestive. It is argued that the technique is feasible but a positive result difficult to interpret.
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J.M.C. Hutchinson, 1990. Control of gastropod shell form via apertural growth rates. Journal of Morphology 206:259–264.

This paper discusses and corrects ideas in Løvtrup and Løvtrup (J. Morphol. 197:53–62,'88) on how differential growth rates around the aperture cause the gastropod shell to coil at particular angles. The relationship between position relative to the shell apex and growth rate is derived. This lets us understand what information on relative growth rates around the aperture is sufficient to determine the shape of the logarithmic spirals that these growth rates generate. I argue that differential growth rates could not be physiologically controlled precisely enough to regulate apical angle; they passively follow, not actively direct, shell shape.
doi link from Wiley Interscience
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J.M.C. Hutchinson, J.M. McNamara & I.C. Cuthill, 1993. Song, sexual selection, starvation and strategic handicaps. Animal Behaviour 45:1153–1177.

Peaks in song output at twilight, particularly dawn are typical of many birds. Recent attention has focused on the honesty of male advertisement, and on whether dawn is a particularly good time for females to assess male quality. In the present model a male divides his time between singing and feeding. If he sings more he is more likely to starve. A natural outcome is that song acts as a strategic handicap and as an honest signal of male quality. By using stochastic dynamic programming, diurnal variation in female assessment is shown to have a profound influence on male daily routines, but dawn is rarely the best time for assessment of quality. Females do not much enhance their probability of pairing with a high-quality male by varying responsiveness to song with time of day; constraints on female time budgets probably have more influence on the timing of male song than does optimization of quality discrimination. But females do greatly enhance their discriminatory efficiency by remembering past song output (song is then more concentrated at certain times, particularly morning, and males may even remain silent on alternate days). In general, the harder the task demanded of a male, the more efficient is the female rule in discriminating male quality.
doi link from Science Direct
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A.I. Houston, J.M. McNamara & J.M.C. Hutchinson, 1993. General results concerning the trade-off between gaining energy and avoiding predation. Philosophical Transactions of the Royal Society of London B 341:375–397.

When animals can choose from a range of feeding options, often those options with a higher energetic gain carry a higher risk of predation. This paper analyses the optimal trade-off between food and predation. We are primarily interested in how an animal’s decisions and its state change over time. Our models are very general. They can be applied to growth decisions, such as choice of habitat, in which case we might consider how the state variable size changes over an animal’s lifetime. Equally our models are applicable to short-term foraging decisions, such as vigilance level, in which case we might consider how energy reserves vary over a day. We concentrate on two cases: (i) the animal must reach a fixed state, its fitness depending on when this is attained; (ii) the animal must survive to a fixed time, its fitness depending on its final state.
In case (i) minimisation of mortality per unit increase of state is optimal under certain baseline conditions. In case (ii) behaviour is constant over time under baseline conditions (the ‘Risk-spreading Theorem’). We analyse how these patterns are modified by complicating factors, e.g. time penalties, premature termination of the food supply, stochasticity in food supply or in metabolic expenditure, and state-dependence in the ability to obtain food, in metabolic expenditure and in predation risk. From this analysis we obtain a variety of possible explanations for why an animal should reduce its intake rate over time (i.e. show satiation). We show how earlier work can be viewed as special cases of our results.
doi link from Royal Society
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G. Noszály, T. Székely & J.M.C. Hutchinson, 1995. Brood survival of Kentish Plovers Charadrius alexandrinus in alkaline grasslands and drained fish ponds. Ornis Hungarica 5:15–21.

We investigated the survival and growth of Kentish Plover Charadrius alexandrinus broods in alkaline grasslands and drained fish-ponds in southern Hungary between 1988 and 1990. Broods that hatched in the bottom of drained fish-ponds survived better (0.985 ± 0.024 (SD) day–1) than the ones hatched in alkaline grasslands (0.851 ± 0.247 day–1). This difference remained significant when we controlled for potentially confounding factors such as brood age, date of hatching and parental care. We propose that fish-ponds were better brood raising habitats than grasslands because they provided more hiding places for the chicks. Growth of chicks, measured by weight gain and tarsus growth, did not differ between the two habitats. These results do not support the earlier suggestion that Kentish Plovers make a wrong decision when they lay their eggs in fish-ponds; offspring produced in fish-ponds have a higher chance of fledging than those produced in grasslands.
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J.M.C. Hutchinson, J.M. McNamara, A.I. Houston & F. Vollrath, 1997. Dyar’s Rule and the Investment Principle: the consequences of a size-dependent feeding rate when growth is discontinuous. Philosophical Transactions of the Royal Society of London B 352:113–138.

We consider animals whose feeding rate depends on the size of structures that grow only by moulting (e.g. spiders’ legs). Our Investment Principle predicts optimum size increases at each moult; under simplifying assumptions these are a function of the scaling of feeding rate with size, the efficiency of moulting and the optimum size increase at the preceding moult. We show how to test this quantitatively, and make the qualitative prediction that size increases and instar durations change monotonically through development. Thus this version of the model does not predict that proportional size increases necessarily remain constant, which is the pattern described by Dyar’s Rule. A literature survey shows that in nature size increases tend to decline and instar durations to increase, but exceptions to monotonicity occur frequently—we consider how relaxing certain assumptions of the model could explain this. Having specified various functions relating fitness to adult size and time of emergence, we calculate (using dynamic programming) the effect of manipulating food availability, time of hatching, and size of the initial (or some intermediate) instar. The associated norms of reaction depend on the fitness function and differ from those when growth follows Dyar’s Rule or is continuous. We go on to consider optimisation of the number of instars. The Investment Principle then predicts upper and lower limits to observed size increases and explains why increases usually change little or decline through development. This is thus a new adaptive explanation for Dyar’s Rule and for the most common deviation from the Rule.
doi link from Royal Society
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J.M.C. HUTCHINSON 1999. Factors influencing the surface fauna of blue holes on South Andros, Bahamas. Bahamas Journal of Science 6:29–43. [A slightly amended version of an article with the same title originally published in 1998 in Cave and Karst Science 25:83–91.]

We surveyed the macrofauna (particularly insects, molluscs and birds) of the surface waters of a series of inland, mostly anchialine, blue holes (flooded caves and associated lakes). The number of species was small, but the fauna varied considerably between holes. The following factors are evaluated as causes of these patterns: isolation and past inundation of Andros island, difficulty of dispersal between holes, topography (size of hole, water depth, whether ringed by cliffs), the surrounding vegetation, water quality (salinity, aeration, nutrients), tidal influence, human disturbance and pollution. Conservation issues are discussed, but generally the surface fauna is shared with far more extensive habitats on Andros. The same conclusion is drawn about the fauna of two subaerial caves associated with blue holes.
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J.M.C. Hutchinson, 1999. Bet-hedging when targets may disappear: optimal mate-seeking or prey-catching trajectories and the stability of leks and herds. Journal of Theoretical Biology 196:33–49.

When a female frog moves towards a calling male, the male may suddenly stop calling and the female have to switch to another male. Analogous situations where “hunters” move towards “targets” that can disappear unpredictably include predators stalking prey and plants growing towards gaps in the canopy. I use dynamic programming to show that when the hunter has a choice of such targets it is optimal to take a curved bet-hedging trajectory, initially heading between two targets so that if one target disappears the other is closer. Also hunters should prefer groups of targets, even if a solitary target is somewhat closer, because it is unlikely that all targets in a group will disappear. Assuming that hunters follow these optimal trajectories I then ask whether it will pay targets to form herds or leks. The extra attractiveness of groups in this model turns out not to be sufficient to outweigh the advantages of herding, but the net benefits of herding are considerably reduced.
doi link from Science Direct
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J.M.C. Hutchinson & J.M. McNamara, 2000. Ways to test stochastic dynamic programming models empirically. Animal Behaviour 59:665–676.

Stochastic dynamic programming (SDP) models are widely used to predict optimal behavioural and life-history strategies. We discuss a diversity of ways to test SDP models empirically, taking as our main illustration a model of the daily singing routine of birds. One approach to verification is to quantify model parameters, but most SDP models are schematic. Because predictions are therefore qualitative, testing several predictions is desirable. How state determines behaviour (the policy) is a central prediction that should be examined directly if both state and behaviour are measurable. Complementary predictions concern how behaviour and state change through time, but information is discarded by considering behaviour rather than state, by looking only at average state rather than its distribution, and by not following individuals. We identify the various circumstances in which an individual’s state/behaviour at one time is correlated with its state/behaviour at a later time. When there are several state variables the relationships between them may be informative. Often model parameters represent environmental conditions that can also be viewed as state variables. Experimental manipulation of the environment has several advantages as a test, but a problem is uncertainty over how much the organism’s policy will adjust. As an example we allow birds to use different assumptions about how well past weather predicts future weather. We advocate mirroring planned empirical investigations on the computer to investigate which manipulations and predictions will best test a model.
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J.M.C. Hutchinson, 2000. Three into two doesn’t go; two-dimensional models of bird eggs, snail shells, and plant roots. Biological Journal of the Linnean Society 70:161–187.

Three published two-dimensional analyses of three-dimensional structures are reinvestigated. (1) In their 1997 paper, Barta & Székely sought shapes of bird eggs that maximised the size of eggs that packed under a circular brood patch. Inappropriately they measured egg size by cross-sectional area; maximising volume implies different optima. Also their genetic algorithm mislocated their optima, probably because of too much mutation. (2) In this journal in 1985, Heath considered a section of an idealised snail shell; altering the overlap of adjacent whorls alters the ratio of shell material to volume enclosed. Heath located an overlap that minimised perimeter/area of the cross-section, which is different from minimising surface-area/volume. I derive the surface area of a logarithmic helicospiral; some formulae used previously are slightly incorrect. Heath’s alteration of overlap changed shell volume and aperture area; a more meaningful reanalysis keeps these characters constant. (3) In 1987, Fitter used a two-dimensional model of plant roots to show that topology, growth rate, and nutrient diffusion rate affect exploitation efficiency (area of nutrient depletion zone/volume of root). Recalculation and reanalysis show that only part of the effect of topology depends on overlap of depletion zones. I compare Fitter’s model to coplanar root systems with three-dimensional depletion zones and then to fully three-dimensional branching. Finally I discuss further examples in which two-dimensional models could mislead.
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J.M.C. Hutchinson, 2000. More on the meanderings of mangabeys; how to test whether bounded walks are random. Functional Ecology 14:267–271.

1. Barrett & Lowen (1998) and Waser (1976) attempted to explain the net monthly and yearly displacements of Grey-Cheeked Mangabeys using observed short-term step lengths and assuming a random walk, with or without boundaries. This paper reanalyses their data.
2. Analytic approaches depend on using the root-mean-square step length, not the mean. However, a more flexible approach to making and testing predictions is Monte-Carlo simulation. With a random walk long-term displacements have a large variance, so a single observation is unlikely to disprove this null hypothesis.
3. Restricting movement to a square lattice is a reasonable approximation even when rectangular boundaries are incorporated. Describing the boundary configuration accurately is more important.
4. The observed non-uniformity in turning angles should have been incorporated as it has a large effect on predicted net displacements, unless the arena is tightly constricted. Randomness of movement within a day can be distinguished from that between days. For Waser’s population it makes sense to predict long-term displacements using only long-distance daily displacements.
5. In conclusion, there are better approaches to establish whether boundaries exist and whether movements follow a random walk.
doi link from Synergy
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H. Reise, J.M.C. Hutchinson, R.F. Forsyth & T. Forsyth 2000. The ecology and rapid spread of the terrestrial slug Boettgerilla pallens in Europe with reference to its recent discovery in North America. The Veliger 43:313–318.

The terrestrial slug Boettgerilla pallens Simroth, 1912, is reported from two sites on Vancouver Island, British Columbia, the first records for this Palaearctic species in America. This paper describes how to recognise the species, and summarises European studies of its ecology. It is unusually worm-like in appearance, lives mostly underground, and occurs in a very wide range of habitats. This century the species has spread remarkably far and fast across Europe from the Caucasus. This is demonstrated by a table of first occurrences in each country, and by three case studies of spread within Great Britain, Belgium and north-west Austria. We predict that it will spread rapidly in North America, and may already occur more widely, but there is no evidence that it will become an important pest.
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R.G. Forsyth, J.M.C. Hutchinson & H. Reise 2001. Aegopinella nitidula (Draparnaud, 1805) (Gastropoda: Zonitidae) in British Columbia—first confirmed North American record. American Malacological Bulletin 16:65–69.

The European land snail, Aegopinella nitidula (Draparnaud, 1805), is reported for the first time from British Columbia, from three sites in the city of Vancouver. These new records are the only documentation of the species in North America, except for two old records that are probably erroneous and have been ignored in recent literature. Comparisons are made between A. nitidula and similar native and introduced species. Information about its ecology in Europe is summarised.
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H. Reise & J.M.C. Hutchinson 2001. Morphological variation in terrestrial slug Deroceras turcicum (Simroth, 1894), and a northern extension of its range in Central Europe. Folia Malacologica 9:63–71.

We report seven new localities of the terrestrial slug Deroceras turcicum (Simroth), including the first occurrences in the Czech Republic and Slovakia. These demonstrate that the distribution of D. turcicum extends much further north than known previously and it might even be rather common there. We discuss possible reasons for its belated discovery. D. turcicum might have often been confused not only with the common D. reticulatum (O.F. Müll.) but also with the syntopical D. rodnae Grossu et Lupu and D. praecox Wiktor. We describe its variability in size, coloration, genital morphology, and caecum length, and consider characters for its reliable discrimination from other species. Two colour morphs (white and violet) are described for the first time. Intriguingly, the coloration of D. turcicum often matches that of congeners found at the same site, which suggests that colour has some selective value. Since external appearance often gives no reason to suspect that two species are present at a site, dissection of several specimens is advisable.
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J.M.B. King & J.M.C. Hutchinson 2001. Site fidelity and recurrence of some migrant bird species in the The Gambia. Ringing and Migration 20:292–302.

Regular ringing was carried out over most of five winters at Ginak in The Gambia. We analyse retrap data from 12 species of migrant birds to examine whether they remain for more than one day within a winter, and whether they return to this area in subsequent winters. We investigate both the rate of recurrence (between-winter retraps within the whole area, approximately 1000 m across) and site fidelity (tendency to be retrapped within 100 m of first capture). Some adjustment of recurrence for annual survival is attempted. For individuals trapped at least twice over a winter, we tabulate the interval between first and last capture: in all 12 species this was over six weeks for some individuals; furthermore, site fidelity within a winter is demonstrated in most species retrapped in reasonable numbers, exceptions were Garden Warbler Sylvia borin and Blackcap Sylvia atricapilla. Most species recurred at appreciable rates in successive seasons, and in three species with a sufficient sample size, Subalpine Warbler Sylvia cantillans, Whitethroat Sylvia communis, and less certainly Olivaceous Warbler Hippolais pallida, the evidence was of site fidelity between winters. We compare recurrence rates with data collected at Djoudj in north Senegal.
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H. Reise, M. Benke & J.M.C. Hutchinson 2002. A sinistral specimen of the terrestrial slug Arion lusitanicus (Gastropoda: Pulmonata: Arionidae). Malakologische Abhandlungen staatliches Museum für Tierkunde Dresden 20:247–252.

A juvenile sinistral specimen of Arion lusitanicus was found near Münster (Germany, Nordrhein-Westfalen) and raised in isolation. Its entire external and internal morphology is a mirror image of normal dextral slugs. In mating experiments with dextral individuals the partners showed clear courtship behaviour but were never successful. This was probably caused by the opposite position of their genital pores, which might make copulation impossible for mirror-image slugs. Reports of sinistral terrestrial slugs are very rare. The authors review earlier cases, and discuss the possible genetic basis of sinistrality in slugs.
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J.M.C. Hutchinson 2002. Two explanations of the dawn chorus compared: how monotonically changing light levels favour a short break from singing. Animal Behaviour 64:527–539.

This paper uses optimality modeling to compare the importance of two of the most plausible and general explanations for the dawn and dusk peaks in bird song output. Kacelnik’s explanation is that foraging is inefficient in poor light, but that social interactions are less affected, making singing more worthwhile than foraging. McNamara et al.’s explanation is based on stochasticity in foraging success and overnight energy requirements; it has been extensively analyzed using stochastic-dynamic-programming models. Both explanations are now incorporated into this sort of model. I use various functions to link success of foraging and singing to light levels, but assume that above some light level there is no further effect. Kacelnik’s explanation indeed has as strong an effect as stochasticity in generating dawn and dusk choruses. Also it predicts short pauses in the singing output just after the dawn chorus and before the dusk chorus. The former arises because birds delay foraging when it will become more profitable later, until foraging success reaches a plateau, when the energetic debt accumulated makes them forage. The principle of this see-saw double switch in behaviors may apply to other explanations for the dawn chorus, and to other shifts in behavior when conditions change gradually. The model predicts that from day to day the cloud cover determines when a dawn chorus starts, but that overnight temperature and wind strength have more effect on chorus strength and duration. I discuss what sort of observational and experimental data on singing routines would better test this model.
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J.M.C. Hutchinson & K. Halupka 2004. Mate choice when males are in patches: optimal strategies and good rules of thumb. Journal of Theoretical Biology 231:129–151.

In standard mate-choice models, females encounter males sequentially and decide whether to inspect the quality of another male or accept one already inspected. What changes when males are clumped in patches and travel between patches is costlier than travel within? With within-patch return costs zero, the optimal policy accepts males above one quality threshold whenever males in the patch remain uninspected; this threshold drops when inspecting the last male in the patch, so returns may only then occur. With within-patch return costs, this two-threshold rule still performs extremely well, but a more gradual decline in threshold is optimal, as it is if discovering the last males in a patch gets harder. Optimal policies become more complex when mean male quality varies between patches or years, and females learn through experiencing male qualities. It can then be optimal to jump patch before inspecting all its males, or, exceptionally, to return to an earlier patch. We compare performance of various rules of thumb in these environments and in ones without a patch structure. The two-threshold rule performs excellently, as do its various simplifications. The best-of-N rule outperforms threshold rules only in non-patchy environments with between-year quality variation. The cutoff rule performs poorly.
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J.M.C. Hutchinson 2005. Is more choice always desirable? Evidence and arguments from leks, food selection, and environmental enrichment. Biological Reviews 80:73–92.

Recent studies on humans show that too much choice can make subjects less likely to choose any item. I consider general adaptive and non-adaptive explanations of why such choice aversion, or its converse, might occur in animals. There are three questions: is more choice always preferred, does it ever lead to less consumption (or a lower probability of consumption), and may it result in worse items being selected? A preference for choice is one of the main explanations for lek formation and I draw attention to previously unrecognised parallels with models of human shopping behaviour. There is indeed evidence of female preference for larger leks, although much of the observational data are open to other interpretations. Unfortunately nobody has looked for choice aversion where it is most to be expected, in leks larger than normally occur. Evidence that too much choice of males confuses females is strongest in acoustically advertising frogs, but the widespread decrease of mating skew in larger leks might also have this explanation. A model reanalyses data on skew in black grouse and suggests that considering only a random subset of a large lek may increase the chances of selecting the better males: larger leks are more likely to include better males, but these are less likely to be selected. These opposing effects may lead to an optimum lek size, but only with a sufficient decline in choice accuracy with size. With food choice, very few studies have avoided confounding choice with food quality, by manipulating only flavour. The widespread phenomena of stimulus-specific satiety and novelty seeking imply that monotonous diets are aversive, but no studies test whether animals choose sites where they know food diversity to be greater. In some insect species even moderate choice of diet can be deleterious, and studies on search images and the confusion effect may be evidence of this in vertebrates. Environmental enrichment of captive animals often relies on increasing the options available, but it need not be the choice itself that is beneficial. I consider briefly further areas in biology where choice preference or aversion are potentially important.
doi link from CUP
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J.M.C. Hutchinson & G. Gigerenzer 2005. Simple heuristics and rules of thumb: where psychologists and behavioural biologists might meet. Behavioural Processes. 69:97–124.

The Centre for Adaptive Behaviour and Cognition (ABC) has hypothesised that much human decision making can be described by simple algorithmic process models (heuristics). This paper explains this approach and relates it to research in biology on rules of thumb, which we also review. As an example of a simple heuristic, consider the lexicographic strategy of Take The Best for choosing between two alternatives: cues are searched in turn until one discriminates, then search stops and all other cues are ignored. Heuristics consist of building blocks, and building blocks exploit evolved or learned abilities such as recognition memory; it is the complexity of these abilities that allows the heuristics to be simple. Simple heuristics have an advantage in making decisions fast and with little information, and in avoiding overfitting. Furthermore humans are observed to use simple heuristics. Simulations show that the statistical structures of different environments affect which heuristics perform better, a relationship referred to as ecological rationality. We contrast ecological rationality with the stronger claim of adaptation. Rules of thumb from biology provide clearer examples of adaptation because animals can be studied in the environments in which they evolved. The range of examples is also much more diverse. To investigate them, biologists have sometimes used similar simulation techniques to ABC, but many examples depend on empirically-driven approaches. ABC’s theoretical framework can be useful in connecting some of these examples, particularly the scattered literature on how information from different cues is integrated. Optimality modelling is usually used to explain less detailed aspects of behaviour but might more often be redirected to investigate rules of thumb.
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J.M.C. Hutchinson & G. Gigerenzer 2005. Connecting behavioural biologists and psychologists: clarifying distinctions and suggestions for further work. Behavioural Processes. 69:159–163.

This article is a reply to the commentaries on our target article, which relates our group’s work on simple heuristics to biological research on rules of thumb. Several commentators contrasted both these approaches with behaviour analysis, in which the patterns of behaviour investigated in the laboratory are claimed to be near-universal attributes, rather than specific to particular appropriate environments. We question this universality. For instance, learning phenomena such Pavlovian or operant conditioning have mostly been studied only in a few generalist species that learn easily; in many natural situations the environment hinders learning as an adaptive strategy. Other supposedly general phenomena such as impulsiveness and matching are outcome models, which several different models of simple cognitive processes might explain. We clarify some confusions about optimisation, optima and optimality modelling. Lastly we say a little more about how heuristics might be selected, learnt and tuned to suit the current environment.
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H. Reise, J.M.C. Hutchinson, R.G. Forsyth & T.J. Forsyth 2005. First records of the terrestrial slug Deroceras turcicum (Simroth, 1894) in Poland. Folia Malacologica 13:177–179.

Deroceras turcicum (Simroth) is reported from six woodland sites around Wałbrzych in southwest Poland. This extension of the species’ range to Poland was expected given the number of reports from adjacent areas of the Czech Republic. We collate these reports as well as local records of Deroceras praecox Wiktor, 1966, which is found in similar habitats. We briefly discuss the difficulty of distinguishing D. turcicum from Deroceras reticulatum (O. F. Müll.), with which it may also co-occur.
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H. Reise, J.M.C. Hutchinson & D.G. Robinson 2006. Two introduced pest slugs: Tandonia budapestensis new to the Americas, and Deroceras panormitanum new to the Eastern USA. Veliger 48:110–115.

This paper reports new findings in North America of two pest slugs from Europe. Tandonia budapestensis, previously unknown from America, was found in Washington DC and near Philadelphia. Deroceras panormitanum, unreported from the Eastern United States and from Eastern North America outside of greenhouses, was found in Washington DC. We describe how to recognize these species and briefly summarize knowledge of their distribution and ecology.
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A. Wilke, J.M.C. Hutchinson, P.M. Todd, & D.J. Kruger 2006. Is risk taking used as a cue in mate choice? Evolutionary Psychology 4:367–393.

More frequent risk taking among young men than women has been explained as a sexually selected trait, perhaps advertising male quality. We investigated this hypothesis in three studies. (1) Young men and women rated how attractive they would find it if a potential partner took various specific risks. A domain-specific risk inventory allowed us to distinguish whether risk taking is attractive generally or only in certain domains. Both sexes reported social and recreational risk taking as attractive (the latter not always significantly so), but other domains of risk taking as unattractive (ethics, gambling, and health) or neutral (investment). The sexes differed markedly little. Parallel studies in Germany and the United States yielded very similar results. (2) We asked subjects to predict how attractive the other sex would find it if the subject performed each risky behavior. Both sexes were rather accurate (which could be merely because they assume that the other sex feels as they do) and sex differences in attractive risk taking are not explicable by sex differences either in attraction or in beliefs about what others find attractive. However, our data could explain why unattractive risks are more often taken by men than women (men slightly underestimated the degree of unattractiveness of such risks, whereas U.S. women overestimated it, perhaps because they themselves found such risk taking more unattractive than did U.S. men). (3) Both members of 25 couples reported their likelihood of engaging in specific risky behaviors, their perception of these risks, and how attractive they would have found these behaviors in their partner. One hypothesis was that, for instance, a woman afraid of heights would be particularly impressed by a man oblivious to such risks. Instead we found positive assortment for risk taking, which might be explained by a greater likelihood of encountering people with similar risk attitudes (e.g. members of the same clubs) or a greater compatibility between such mates. Finally, contrary to the assumption that taking a low risk is likely to be less revealing of an individual’s quality than taking a high risk, we found a strong negative relationship between the perceived riskiness of a behavior and how attractive it was judged.
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H. Reise, S. Visser & J.M.C. Hutchinson 2007. Mating behaviour in the terrestrial slug Deroceras gorgonium: is extreme morphology associated with extreme behaviour? Animal Biology 57:197–215.

Mating in Deroceras consists of an investigation phase (precourtship), then a long courtship involving mutual stroking with the extruded sarcobelum, then sperm exchange (copulation). The penial gland, if present, everts over the partner’s skin during copulation: this is hypothesised to apply a secretion manipulating the partner to use received sperm. Deroceras gorgonium has a particularly large penial gland, divided into many finger-like branches. We studied D. gorgonium mating behaviour in the hope of further indications of the gland’s function. Precourtship and courtship together last longer than in other Deroceras (c. 6 h to >9 h); precourtship is highly variable, often with many bouts of different behaviours, including seemingly inactive phases. During most of the courtship partners remain apart waving their particularly long, pointed sarcobela; only at a later stage do the tips of these contact the partner. This waving alternates with circling for half a turn. For the first time in Deroceras we observed the sarcobelum transferring a secretion. The copulation is amongst the fastest: genital eversion and sperm exchange occur within 1 s, and slugs separate 18–25 s later. The penial gland is everted immediately after sperm exchange, but, surprisingly, is often spread underneath the partner rather than over its back and, if on top, is not always fully spread over the partner’s body. We discuss these observations with respect to penial gland morphology and in the light of possible sexual conflicts. The long courtship and distant sarcobelum waving might reflect attempts to transfer, but not receive, secretion, and the circling might serve size assessment.
doi link from Ingenta
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J.M.C. Hutchinson & P.M. Waser 2007. Use, misuse and extensions of “ideal gas” models of animal encounter. Biological Reviews 82:335–359.

Biologists have repeatedly rediscovered classical models from physics predicting collision rates in an ideal gas. These models, and their two-dimensional analogues, have been used to predict rates and durations of encounters among animals or social groups that move randomly and independently, given population density, velocity, and distance at which an encounter occurs. They have helped to separate cases of mixed-species association based on behavioural attraction from those that simply reflect high population densities, and to detect cases of attraction or avoidance among conspecifics. They have been used to estimate the impact of population density, speeds of movement and size on rates of encounter between members of the opposite sex, between gametes, between predators and prey, and between observers and the individuals that they are counting. One limitation of published models has been that they predict rates of encounter, but give no means of determining whether observations differ significantly from predictions. Another uncertainty is the robustness of the predictions when animal movements deviate from the model’s assumptions in specific, biologically relevant ways. Here, we review applications of the ideal gas model, derive extensions of the model to cover some more realistic movement patterns, correct several errors that have arisen in the literature, and show how to generate confidence limits for expected rates of encounter among independently moving individuals. We illustrate these results using data from mangabey monkeys originally used along with the ideal gas model to argue that groups avoid each other. Although agent-based simulations provide a more flexible alternative approach, the ideal gas model remains both a valuable null model and a useful, less onerous, approximation to biological reality.
doi link from Synergy
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J.M.C. Hutchinson & S.C. Griffith 2008. Extra-pair paternity in the Skylark Alauda arvensis. Ibis 150:90–97.

We present the first quantitative data on the genetic breeding system of a lark (Alaudidae), the Skylark Alauda arvensis. Using a set of eight microsatellite loci, we genotyped 171 offspring from 52 broods of Skylark and detected 35 extra-pair offspring (20%), in 14 different broods (27%). All offspring matched their putative mother, so there was no evidence of intraspecific brood parasitism. Previous non-genetic studies had suggested that the species was predominantly socially monogamous, with only rare occurrences of social polygyny and polyandry, although some behaviours, such as mate guarding, did suggest the possibility of extra-pair copulations. The relatively high level of EPP in this species is likely to affect the variation in male reproductive success because extra-pair paternity was non-randomly distributed amongst males, with those with shorter wings more likely to be cuckolded.
doi link from Synergy
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J.M.C. Hutchinson, A. Wilke & P.M. Todd 2008. Patch leaving in humans: can a generalist adapt its rules to dispersal of items across patches? Animal Behaviour 75:1331–1349.

We used a computer game to examine three aspects of patch-leaving decisions in humans: how well do humans perform compared to the optimal policy, can they adjust their behaviour adaptively in response to different distributions of prey across patches, and on what cues are their decisions based? Subjects earned money by catching fish when they briefly appeared within a pond; the timing of appearances was stochastic but at a rate proportional to how many fish remained. Caught fish were not replaced and ponds varied in how many fish they initially contained (according to three different distributions). At any point subjects could move to a new pond, but “travel” took some time. They delayed this switch much too long. Furthermore, regardless of the distribution of prey, subjects spent longer at ponds where they had found more items (contrary to optimality predictions in two of the environments). However, they apparently responded not to the number of captures directly (despite this appearing on screen), but to the current interval without a capture, to the interval before the last capture, and to time at the current pond. Self reports supported this order of cue importance. Subjects often left directly after a capture, perhaps an example of the Concorde fallacy. High success rate in the preceding patch decreased residence time and subjects seemed to be learning to leave earlier over the latter two thirds of the experiment. Minimisation of delay to the next capture alone might explain some of the suboptimal behaviour observed.
doi link from ScienceDirect
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A. Wilke, J.M.C. Hutchinson, P.M. Todd, & U. Czienskowski 2009. Fishing for the right words: decision rules for human foraging behavior in internal search tasks. Cognitive Science 33:497–529.

Animals depleting one patch of resources must decide when to leave and switch to a fresh patch. Foraging theory has predicted various decision mechanisms; which is best depends on environmental variation in patch quality. Previously we tested whether these mechanisms underlie human decision making when foraging for external resources; here we test whether humans behave similarly in a cognitive task seeking internally generated solutions. Subjects searched for meaningful words made from random letter sequences, and as their success rate declined, they could opt to switch to a fresh sequence. As in the external foraging context, time since the previous success and the interval preceding it had a major in?uence on when subjects switched. Subjects also used the commonness of sequence letters as a proximal cue to patch quality that in?uenced when to switch. Contrary to optimality predictions, switching decisions were independent of whether sequences differed little or widely in quality.
doi link from Synergy
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J.M.C. Hutchinson & H. Reise 2009. Mating behaviour clarifies the taxonomy of slug species defined by genital anatomy: the Deroceras rodnae complex in the Sächsische Schweiz and elsewhere. Mollusca. 27:183–200.

Collections of Deroceras from the uplands south of Dresden (along the Czech-German border) revealed two similar species differing in mating behaviour. The ranges interdigitate, but the species never occurred together. Species A has a wide sarcobelum held leftwards over its head and the everted penes are fully visible from above. It most resembles Deroceras praecox, occurring 100 km further east, whose anatomy and courtship behaviour are nevertheless consistently distinct; if these are different species, species A appears endemic to the Sächsische Schweiz. In species B, courtship and copulation take longer. Its sarcobelum is narrower, with a much enlarged base, and is directed forward or to the right. Most distinct is that the penes evert downwards and coil round each other for an additional revolution; their eversion is hidden from above except for the hand-like penial gland. This species is conspecific with Swiss, German and Austrian populations of Deroceras rodnae, but distinct from eastern populations, which more closely resemble D. praecox and species A. Unpublished molecular analyses support this division. Nevertheless, identifying non-mating animals by genital anatomy can be difficult: the base of the sarcobelum provides the best character. Western populations of D. rodnae should be termed Deroceras juranum Wüthrich, 1993.
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H. Reise, J.M.C.Hutchinson, S. Schunack & B. Schlitt 2011. Deroceras panormitanum and congeners from Malta and Sicily, with a redescription of the widespread pest slug as Deroceras invadens n. sp. Folia Malacologica 19:201–223.

The name Deroceras panormitanum is generally applied to a terrestrial slug that has spread worldwide and can be a pest; earlier this tramp species had been called Deroceras caruanae. Neither name is appropriate. The taxonomic descriptions apply to a species from Sicily and Malta. This true D. panormitanum and the tramp species are distinct in morphology and mating behaviour. For instance, the penial caecum of D. panormitanum is more pointed, everting faster at copulation. The size of the penial lobe varies considerably in preserved specimens but is always prominent at copulation. D. panormitanum is distinct from the Maltese endemic Deroceras golcheri, but a phylogeny based on COI mtDNA implies that they are more closely related than is the tramp species. D. golcheri has a still closer counterpart on Sicily, but we leave the taxonomy of this “species X” unresolved. In interspecific crosses, D. panormitanum may transfer sperm to the partner’s sarcobelum whereas the partner fails to evert its penis (D. golcheri) or to transfer sperm (the tramp species). Names previously applied to the tramp species originally referred to D. panormitanum or are otherwise invalid, so it is here formally redescribed as D. invadens. Deroceras giustianum Wiktor, 1998 is synonymised with D. panormitanum.
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J.M.C.Hutchinson, C. Fanselow & P.M. Todd 2012. Car parking as a game between simple heuristics. Pp. 454–484 (Chapter 18) in P.M. Todd, G. Gigerenzer & the ABC Research Group (Eds), Ecological rationality: intelligence in the world. New York: Oxford University Press.

The chapter is published without an abstract, but we provided the following to OUP for publicity purposes:
Selecting a parking space is a sequential-search problem. Intriguingly, where others have parked determines the pattern of spaces available. Earlier optimality models of parking ignored this game-theoretic aspect, unrealistically assuming random occurrences. This chapter instead simulates populations of cars: agents (drivers) may accept any unoccupied space as they proceed down a dead-end street towards the destination; otherwise they take the first as they drive back out. Several simple decision heuristics are considered, inspired by those from other sequential-search domains. Parameter values generating Nash equilibria are sensitive to conditions and performance criteria. An evolutionary algorithm allows the different heuristics to compete. The winner exploits the emergent environment structure: since adjacent sites often fill sequentially, they empty at similar times, so recently encountered spaces predict more spaces ahead. But high car densities may arise far from the destination, so additionally the winner rejects spaces until within a fixed distance of the destination.
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J.M.C. Hutchinson, D.W. Stephens, M. Bateson, I. Couzin, R. Dukas, L.-A. Giraldeau, T.T. Hills, F. Méry & B. Winterhalder 2012. Searching for fundamentals and commonalities of search. Pp. 47–65 (Chapter 4) in P.M. Todd, T.T. Hills & T.W. Robbins (Eds), Cognitive search: Evolution, algorithms, and the brain. Strüngmann Forum Reports Vol. 9. Cambridge, MA: MIT Press.

This chapter reports the discussion of a group of mostly behavioral biologists, who attempt to put research on search from their own discipline into a framework that might help identify parallels with cognitive search. Essential components of search are a functional goal, uncertainty about goal location, the adaptive varying of position, and often a stopping rule. The chapter considers a diversity of cases where search is in domains other than spatial and lists other important dimensions in which search problems differ. One dimension examined in detail is social interactions between searchers and searchers, targets and targets, and targets and searchers. The producer-scrounger game is presented as an example; despite the extensive empirical and theoretical work on the equilibrium between the strategies, it is largely an open problem how animals decide when to adopt each strategy, and thus how real equilibria are attained. Another dimension that explains some of the diversity of search behavior is the modality of the information utilized (e.g., visual, auditory, olfactory). The chapter concludes by highlighting further parallels between search in the external environment and cognitive search. These suggest some novel avenues of research.
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E. Dreijers, H. Reise & J.M.C. Hutchinson 2013. Mating of the slugs Arion lusitanicus auct. non Mabille and A. rufus (L.): different genitalia and mating behaviours are incomplete barriers to interspecific sperm exchange. Journal of Molluscan Studies 79:51–63.

The large slug known as Arion lusitanicus (or A. vulgaris) is an important pest that is spreading through much of Europe. Arion rufus disappears at sites where A. lusitanicus has established strong populations. The finding of morphological intermediates suggests that A. lusitanicus hybridizes with A. rufus, but interspecific mating had not been proven. Considering the marked differences in their genitalia, it has been hard to envisage how mixed couples might transfer sperm. Arion lusitanicus and A. rufus were collected from pure populations near Görlitz, Germany, and used for laboratory mating trials involving either two individuals of A. rufus (henceforth RR), two of A. lusitanicus (LL), or one of each species (mixed). Matings were video recorded and some couples were killed during or after copulation to study spermatophore transfer and genital anatomy during mating. Three mixed pairs copulated. However, mixed pairs were significantly less likely to copulate than either RR or LL pairs (7% vs 52% and 36%). At each stage of mating, the probability of proceeding further was lower in mixed pairs than predicted from rates in RR and LL pairs, but this effect was strongest for yin-yang formation and initiating copulation. One problem was that A. lusitanicus tried to circle after yin-yang formation, whereas A. rufus remained stationary. In this respect, and in the repositioning of its everted oviduct, it was A. lusitanicus that compromised. LL copulations lasted over twice as long as RR copulations, but spermatophore formation took similar times, permitting reciprocal spermatophore exchange in mixed couples even though their copulations ended much earlier than in LL pairs. Our observations of mating behaviour of intraspecific pairs largely agree with previous descriptions of A. rufus, but we discuss some discrepancies with the fuller descriptions available for A. lusitanicus.
doi link to journal
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J.M.C. Hutchinson & H. Reise 2013. A persisting population of an introduced slug, Milax nigricans, in Dunkirk, France. Mitteilungen der deutschen malakozoologischen Gesellschaft 89:35–38.

A population of Milax nigricans was found on February 19th 2011 outside a block of flats in Dunkirk, France. It was persisting 21 month later. This is the second finding in the department of Nord. We review earlier occurrences of the species outside its normal range in the Mediterranean and illustrate the most important identification characters.
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J.M.C. Hutchinson, H. Reise & D.G. Robinson 2014. A biography of an invasive terrestrial slug: the spread, distribution and habitat of Deroceras invadens. Neobiota 23: 17–64.

The article reviews distribution records of Deroceras invadens (previously called D. panormitanum and D. caruanae), adding significant unpublished records from the authors’ own collecting, museum samples, and interceptions on goods arriving in the U.S.A. By 1940 D. invadens had already arrived in Britain, Denmark, California, Australia and probably New Zealand; it has turned up in many further places since, including remote oceanic islands, but scarcely around the eastern Mediterranean (Egypt and Crete are the exceptions), nor in Asia. Throughout much of the Americas its presence seems to have been previously overlooked, probably often being mistaken for D. laeve. New national records include Mexico, Costa Rica, and Ecuador, with evidence from interceptions of its presence in Panama, Peru, and Kenya. The range appears limited by cold winters and dry summers; this would explain why its intrusion into eastern Europe and southern Spain has been rather slow and incomplete. At a finer geographic scale, the occurrence of the congener D. reticulatum provides a convenient comparison to control for sampling effort; D. invadens is often about half as frequently encountered and sometimes predominates. Deroceras invadens is most commonly found in synanthropic habitats, particularly gardens and under rubbish, but also in greenhouses, and sometimes arable land and pasture. It may spread into natural habitats, as in Britain, South Africa, Australia and Tenerife. Many identifications have been checked in the light of recent taxonomic revision, revealing that the sibling species D. panormitanum s.s. has spread much less extensively. A number of published or online records, especially in Australia, have turned out to be misidentifications of D. laeve.
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J.M.C. Hutchinson & H. Reise 2015. Mating in Ariunculus isselii, an arionid slug without a spermatophore. Journal of Molluscan Studies 81: 247–258.

Ariunculus is a genus of terrestrial slugs often treated as a subgenus of Arion. A survey of the literature reveals doubts about many of the described species: only A. speziae and A. isselii are now generally recognized as belonging to Ariunculus. Ariunculus isselii is widespread on Sardinia. We describe its external appearance, mating behaviour and genital anatomy, and interpret the functioning of the genitalia based on specimens killed during copulation or shortly afterwards. Instead of the distinct epiphallus of Arion, there is only a small ampulla, because sperm are pumped out piecemeal to the recipient rather than transferred in a spermatophore. We speculate (in a framework of sexual selection theory) that this may explain why mating lasts 12 h after the initial genital eversion, much longer than in most Arion. The absence of a spermatophore provides grounds for keeping Ariunculus separate from Arion. Similarly to some Arion species, the papilla is inserted into the partner’s partially everted bursa trunk; we discuss four different hypotheses for the function of this arrangement. Also as in some Arion species, the oviduct is everted during mating so as to apply a ligula. We provide information on egg laying in captivity and report that the species can self-fertilize.
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A. Ludwig, H. Reise & J.M.C. Hutchinson 2015. Die Nacktschneckenfauna in Gärten der Stadt Görlitz (Sachsen, Deutschland). Berichte der naturforschenden Gesellschaft der Oberlausitz 23: 43–57.

The slug fauna of gardens in the town of Görlitz was investigated by hand searching 14 house gardens, 13 allotments and four courtyards. The 13 species that were found were, in decreasing order of occurrence, Arion lusitanicus auct. non Mabille, Deroceras reticulatum, Arion distinctus, Deroceras invadens, Arion fasciatus, Limax maximus, Boettgerilla pallens, Deroceras sturanyi, Arion rufus, Arion silvaticus, Lehmannia valentiana, Arion circumscriptus und Deroceras laeve. More species of slug occurred in gardens rated as untidier (p = 0.02). The discovery of L. valentiana is the first outdoors record for Görlitz. The diverse state of establishment of the other four invasive species is discussed in relation to earlier faunistic data. Our investigation provides a baseline for long-term monitoring of the development of the slug fauna in Görlitz.
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J.M.C. Hutchinson & H. Reise 2015. An invasion from Germany; Deroceras invadens (Pulmonata, Agriolimacidae) and other synanthropic slugs in the southwest corner of Poland. Folia Malacologica 23: 301–307.

Ten towns in the southwest corner of Poland within 57 km of the German border were surveyed for slugs. Deroceras invadens was found only in the four westernmost towns. In Zgorzelec, which was surveyed more intensively than the other towns, it occurs widely but only sporadically. Although D. invadens had been known in the adjacent German town of Görlitz since 1991, hitherto the only Polish record was from Wrocław, 140 km to the east. This pattern suggests a new colonisation across the border. Amongst the other species, one surprise was the rarity of Deroceras reticulatum in several towns, and another that Arion fuscus was common in one town but not found in any of the others. Records of Deroceras praecox extend its known range in Poland further west. Contrary to expectations from the literature, Deroceras sturanyi was adult in spring, and reproducing at a small size typical of Deroceras laeve.
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J.M.C. Hutchinson, H. Reise & G. Skujienė 2017. Life cycles and adult sizes of five co-occurring species of Arion slugs. Journal of Molluscan Studies 83: 88–105.

Five species of Arion slugs were collected repeatedly at a woodland site in southern England and all individuals weighed. Selected samples of these were dissected so as to weigh components of the reproductive tract. The relative weights of the gonad, spermoviduct and albumen gland provided the basis to categorize individuals into adult, subadult or immature classes, or as juvenile if the sum of these weights was below a threshold. This procedure was validated by raising A. subfuscus in captivity and killing at a range of known ages before and after egg laying. In the other species, organ weights from individuals observed to have laid eggs or mated also helped to calibrate the divisions. Such data from two species demonstrated that, following the production of an egg clutch, the albumen gland took days gradually to regrow. There was little evidence of much variation in life cycle from year to year and the broad patterns, although not precise timings, agreed with studies elsewhere. No species produced more than one generation per year and in all there was a season (brief in A. subfuscus) when adults were absent. The life cycles were predominantly annual, although in some species a minority of individuals might take 18 months to mature. The time of year at which individuals matured into adults varied between species: A. intermedius in August and September, A. distinctus mostly in December and January, A. circumscriptus mostly January to April, A. subfuscus April to early October and A. rufus July to September. The largest two species thus dominated in summer, but at other times the species overlapped considerably in size. In four species, individuals maturing later in the season did so at a smaller size; the possible exception was A. intermedius, in which maturation was highly synchronized. The coefficients of variation in adult size were compared against a collection of such data from other terrestrial molluscs. The smallest species, A. intermedius, had disproportionately large hatchlings.
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J.E. Maunder, R.G. Noseworthy, J.M.C. Hutchinson & H. REISE 2017. Terrestrial molluscs of the Province of Newfoundland and Labrador, Canada. Part 1: Boettgerillidae. Checklist 13: 277–284.

The family Boettgerillidae, represented by the Eurasian slug Boettgerilla pallens Simroth, 1912, is first recorded for Newfoundland and Labrador, Canada —a range extension of almost exactly 5000 km within the Americas. Compiled, within an appendix, to provide a national perspective for the Newfoundland and Labrador record, are 13 previously unpublished B. pallens records from British Columbia, Canada. Incidentally recorded is the second eastern Canadian outdoor occurrence of the European slug Deroceras invadens. This paper is the first in a series that will treat all of the terrestrial molluscs of Newfoundland and Labrador.
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H. Reise, B. Schlitt & J.M.C. Hutchinson 2018. Bericht über die 33. Regionaltagung des Arbeitskreises Ost der DMG in Ostritz bei Görlitz vom 23. bis 25. September 2016: Mollusken des Rotsteins bei Sohland, Sachsen. Mitteilungen der deutschen malakozoologischen Gesellschaft 98:35–44.

The 33rd eastern German malacological meeting took place on 23rd to 25th September 2016 in the Internationales Begegnungszentrum St Marienthal in Ostritz, eastern Saxony. There were 35 participants, including accompanying persons. The excursion on 24th September, focussing on terrestrial molluscs, visited three collecting sites in the hilly area southwest of Görlitz: the protected area of the basalt massif Rotstein near Sohland am Rotstein, a pond and alder wood near Sohland, and the basalt hill Eichler at Rennersdorf. Further collections were made around the monastery of St Marienthal, Ostritz. The collections yielded 81 mollusc species, 53 of those from the main target area, the Rotstein. Ten species were found on the Rotstein for the first time. In total, 61 species have now been recorded from the Rotstein, which underlines its special significance for the Upper Lusatian malacofauna. Faunistically interesting species include Vertigo alpestris, Euomphalia strigella, Truncatellina cylindrica and Vitrea subrimata. The latter was found in Upper Lusatia for the first time. This is also the case for a shell of a juvenile Nesovitrea petronella found in alder wood next to the pond at Sohland. Further noteworthy collections include Vitrinobrachium breve from the Eichler and Limacus flavus from Ostritz, both found for the first time in the Saxonian part of Upper Lusatia outside of Görlitz. Unfortunately, Arion lusitanicus was found in the central areas of the protected woodland of the Rotstein, demonstrating its invasion of natural habitats, where it currently co-occurs with the native A. rufus agg.
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H. Reise, Z. Arslangündoğdu, B. Schlitt, J.M.C. Hutchinson, E. Hızal & E. Bacack 2018. First records of the terrestrial slug Arion ater s.l. (Linnaeus, 1758) (Pulmonata: Arionidae) from Turkey. Folia Malacologica 26: 213–220.

A strong population of the terrestrial slug Arion ater s.l. is reported from the European and Asian parts of Istanbul, Turkey. This is the first confirmed report of this large, conspicuous taxon from Turkey and from Asia. Our samples from five synanthropic sites indicate that it is already well established. Partial sequences of the mitochondrial COI gene (cytochrome c oxidase subunit I) place the Turkish slugs in a small clade shared with a few specimens from western France, perhaps indicating the origin of the Istanbul population. The next closest haplotypes (9% difference) fall within the clade identified as Arion ater s.s. This fits with the genital morphology of the Turkish slugs, which is most similar to the ater-form of A. ater s.l. Our discovery also puts a new light on the recent report of the highly invasive pest slug Arion lusitanicus auct. non Mabille, 1868 (often called Arion vulgaris Moquin-Tandon, 1855) in Isparta, which was identified only on the basis of external morphology. As reliable morphological distinction of these two species requires examination of the genital anatomy, the specimen from Isparta should be reinvestigated.
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J.M.C. Hutchinson, B. Schlitt & H. Reise 2019. Monacha claustralis (Rossmässler 1834), a hygromiid snail new to Germany. Mitteilungen der deutschen malakozoologischen Gesellschaft 100: 17–22.

Colonies originally identified as Monacha cartusiana have often turned out to be M. claustralis. This was the case with a sample collected in 2016 from near Jena, and thus the first record of M. claustralis from Germany. We compare these animals' genital anatomy against several distinguishing characters advocated in the literature. A partial-COI sequence indicates a close genetic relationship with Polish colonies near Gdansk and Kielce. Although originally from western Turkey and adjacent parts of the Balkan Peninsula, M. claustralis is liable to have established itself at other sites in Germany, maybe sometimes hidden in mixed colonies with M. cartusiana, from which it is indistinguishable using external characters.
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H. Reise, A.-K. Schwarzer, J.M.C. Hutchinson & B. Schlitt 2020. Genital morphology differentiates three subspecies of the terrestrial slug Arion ater (Linnæus, 1758) s.l. and reveals a continuum of intermediates with the invasive A. vulgaris Moquin-Tandon, 1855. Folia Malacologica 28: 1–34.

The terrestrial slug Arion vulgaris Moquin-Tandon (= A. lusitanicus auct. non Mabille) is an important agricultural pest that has invaded much of Europe. Previous work has demonstrated hybridisation with A. ater (Linnæus) s.l. We describe the genital anatomy of morphological intermediates found in eastern Saxony (Germany), comparing them with the parent species. We recommend a standard method of genital dissection and consider a set of five genital characters. The intermediates demonstrate the homology of the ligula-bearing organs of the two species; the ancestral position of the ligula in the dilated part of the oviduct has moved to the upper atrium in A. ater s.l. Furthermore we differentiate three morphotypes of A. ater s.l. in eastern Saxony, associated with different mitochondrial DNA sequences. One is A. ater ater, previously unrecognised from this part of Germany and the Czech Republic. The two other morphotypes correspond to the predominantly British and the Continental subspecies previously recognised on genetic and morphological grounds. We designate as the lectotype of Limax rufus Linnæus, 1758 a non-surviving specimen from Almondbury, England, described by Lister; thus the predominantly British subspecies becomes A. ater rufus. The appropriate name for the Continental form is A. ater ruber (Garsault, 1764).
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J.M.C. Hutchinson, B. Schlitt, T. Kořínková, H. Reise & G.M. Barker 2020. Genetic evidence illuminates the origin and global spread of the slug Deroceras invadens. Journal of Molluscan Studies 86: 306–322.

The terrestrial slug Deroceras invadens has spread across much of the world over the last century. What is to learn from mitochondrial sequences (partial COI) about the species’ origin, colonisations, and diversity? Samples from 317 localities covering most of its range yielded 87 haplotypes. Higher diversity, the predominance of private haplotypes, and geographic structuring all indicate a native range centred on southern Italy, including eastern Sicily. In contrast, central Italy is dominated by one haplotype, although accompanied by both close and more distant relatives; the lack of geographic structuring suggests recent expansion from a restricted distribution within that region. Beyond the Alps, two haplotypes predominate, accompanied by very similar variants; such star-shaped genealogies characterise recent population growth. Also some rarer haplotypes have been independently introduced. Generally haplotypes are well mixed here, often co-occurring at a locality. In North America and Australasia, some frequent haplotypes were likely directly introduced from Italy, because they were not found elsewhere in Europe. The rarity or absence in these continents of one or other of the two dominant European haplotypes suggests that import inspections have restricted repeated introductions. A skyline plot detects the recent demographic expansion but also indicates an earlier population decline in the native area. This may explain why the one-dimensional summary statistics FS and R2 did not signal population growth. A review of 41 other studies that used DNA to analyse invasions of terrestrial molluscs documents considerable diversity in methodology. Studies using genetic data to date recent invasions probably should adjust standard substitution rates upwards.
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J.M.C. Hutchinson, H. Reise & B. Schlitt (in press). Mating behaviour and genital anatomy of Deroceras cecconii (Pollonera, 1896), a widespread but overlooked slug from Italy, now introduced to eastern Germany. Archiv für Molluskenkunde 149: 221–236.

The terrestrial slug Deroceras cecconii was described from Vallombrosa, a forest in the hills above Florence, Italy. However, its validity has long been disbelieved. Fresh samples from the type locality agreed well with the original description and proved to be distinct in genital anatomy, mating behaviour and COI genetic sequence. Video recordings of the copulation showed that, besides the penial gland, the penis had 2 pockets that evert, the caecum and lobe. The caecum deposits sperm onto the partner’s penis but is short and not always apparent in the retracted state. Many other components of the mating behaviour are modifications of those observed in D. invadens, D. panormitanum and D. golcheri, but the molecular phylogeny, based on the mitochondrial COI gene, did not fully resolve their relationships. Genetically closest to D. cecconii was a slug from the island of Montecristo previously considered possibly to be D. golcheri. Deroceras golcheri and an undescribed close relative from Sicily are liable to be confused with D. cecconii anatomically, but D. cecconii is distinguished by the presence of a lobe and the concave saddle at the proximal end of the penis where the vas deferens inserts. The penis of D. cecconii is less similar to those of D. invadens and D. panormitanum, which both have a long caecum and, usually, lobe. Deroceras cecconii is common and widespread in much of Italy, although not the far south, occurring in a wide range of habitats. Also, a local but persistent population has been introduced to the town of Ostritz on the eastern border of Germany. The genetic uniformity amongst most populations raises the possibility that it might also be an introduction within part of its Italian range.
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View a video of the copulation.
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J.M.C. Hutchinson & M. Bender (awaiting resubmission). Choice of toilet cubicle: a test of apparent foresight in a spatial game.

We test whether individuals exhibit apparent foresight in an everyday spatial game. We occupied the first and last toilet cubicles in a row of seven; the remainder are numbered 1 to 5. A substantial minority of users chose the first cubicle encountered, not minding a neighbor. Others that avoid neighbors might do best to choose Cubicle 2 or 4, allowing a later arrival space to locate away from them. Cubicle 3 (maximizing immediate separation) was indeed less popular than Cubicle 2, and at one site also than Cubicle 4. Cubicle 2’s popularity suggests foresight, but is also explicable by a satisficing heuristic. We envisage that unconscious rules of thumb learnt in other contexts lead to behavior adapted to responses of later arrivals. Day of week, time of day, busyness and duration on the toilet each affected the pattern of choice. We investigated this game further by closing a third cubicle.
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H. Reise, V. Barth & J.M.C. Hutchinson (awaiting resubmission). Genital polymorphism in the hermaphroditic slug Deroceras laeve: the influence of environment and age.

Phally polymorphism (the coexistence of individuals with complete and incomplete male genitalia) has arisen several times independently amongst the pulmonates. Unlike the two or three distinct penis morphs in other polymorphic species, the terrestrial slug D. laeve exhibits a continuous array of penis morphs. We classified the morphs into five types: euphallics, complete aphallics and 3 intermediates. The intermediate types 2 and 3 differ mainly in whether the vas deferens connects to the penis. We investigated what factors influenced phally morph in three laboratory experiments: one tested whether different phally morphs merely represent successive ontogenetic stages; the other two examined the influence of temperature and density. Body weights were measured as a possible indication of resource reallocation. We also monitored three field populations; these differed significantly in the proportions of the phally morphs. In the experiments, the overall correlation between phally type and body weight was not significant, although in two treatment groups the more reduced morphs were significantly heavier. Individuals kept at high density were smaller and started egg laying later, but no influence of density on the phally type could be detected. The absence of potential mating partners neither inhibited development of male genitalia nor was correlated with euphally (disproving the proposal that apophallation by a mating partner is responsible for the reduced penis morphs). Different age classes (60–90 days from hatching) did not differ in the percentages of phally types, disproving the idea of proterogyny. However, slugs raised at 15°C belonged significantly more often to the more reduced phally types 1–2 than slugs raised at 8°C. No similar tendency could be detected in the field populations, which did not show any convincing seasonal pattern in phally, possibly owing to small sample sizes at some collecting dates. The effect of temperature in our laboratory study is opposite in direction to that found by Nicklas & Hoffmann (1981) in North American D. laeve. The two studies are compared.
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