Intersexual Differences in Behaviour and Resource Use of Specialist Phengaris teleius Butterflies

Simple Summary

In this study, we compared intersexual differences in behaviour and resource use of well-known Scarce Large Blue butterflies. The results indicated that females take short, but exceptionally regular flights, exploring available resources for oviposition. Males took longer, less regular flights, characterised by frequent interactions in search for receptive females. Interestingly, interactions between conspecific butterflies of the investigated species lasted significantly longer than with other species, especially when different sexes were involved. This suggests that individuals were able to quickly and efficiently recognise potential mating partners. Finally, the focal species showed strong association with its larval host plant while resting and nectaring, and less so with other plants with similarly coloured and shaped flowers. Females were particularly strongly restricted to the larval host plant, which provides some evidence that their sensory system shows neural limitation towards this valuable resource.

Abstract

Although the behaviour of the Large Blue butterflies of the genus Phengaris (= Maculinea) is relatively well studied, most empirical data come from investigations of their dispersal and oviposition. Here, we assessed overall intersexual differences in resource use by tracking Phengaris teleius (Bergsträsser, 1779) individuals and recording the duration of their behaviours. Females were characterised by frequent, short flights, and devoted more time to resting and oviposition. Males engaged in numerous, but usually short interactions, and spent most of the time in flight exploring their surroundings for receptive females. Their average flight time was significantly longer compared to females. Average feeding time did not differ between the sexes but was shorter when butterflies were feeding on Sanguisorba officinalis L. Intraspecific interactions within P. teleius were three times longer than those with other insect species, and interactions between sexes were particularly long lasting. Significantly shorter interspecific interactions imply that butterflies can easily recognise conspecifics and differentiate between sexes, which offers obvious fitness benefits. Both sexes, but especially females, showed strong association with their larval host plant, and less so with other flowers of similar colour and shape. Females predominantly used their host plant for feeding, which possibly indicates neuro-sensory constraints towards this resource.

The "sequential cues hypothesis": a conceptual model to explain host location and ranking by polyphagous herbivores

Successfully locating a host plant is crucial for an insect herbivore to feed and/or oviposit. However, locating a host within a complex environment that may contain an array of different plant species is a difficult task. This is particularly the case for polyphagous herbivores, which must locate a host within environments that may simultaneously contain multiple suitable and unsuitable hosts. Here we review the mechanisms of host selection used by polyphagous herbivores, as well as exploring how prior experience may modify a generalist's response to host cues. We show that recent research demonstrates that polyphagous herbivores have the capacity to detect both common cues from multiple host species, as well as specific cues from individual host species. This creates a paradox in that generalists invariably rank hosts when given a choice, a finding at odds with the "neural limitations" hypothesis that says generalist insect herbivores should not have the neural capacity to identify cues specific to every possible host. To explain this paradox we propose a model, akin to parasitoid host location, that postulates that generalist herbivores use different cues sequentially in host location. We propose that initially common host cues, associated with all potential hosts, are used to place the herbivore within the host habitat and that, in the absence of any other host cues, these cues are sufficient in themselves to lead to host location. As such they are true "generalist" cues. However, once within the host habitat, we propose that the presence of a smaller group of cues may lead to further host searching and the location of preferred hosts: these are "specialist" cues. This model explains the current conflict in the literature where generalists can respond to both common and specific host-plant cues, while also exhibiting specialist and generalist host use behavior under different conditions.

Host plant acceptance in a generalist insect: threshold, feedback or choice?

Generalist insect herbivores feed mainly on one or more primary host species, but unlike specialists they also accept numerous secondary hosts. This raises the question of how generalists retain a broad host range yet allocate most of their eggs to primary hosts. We considered three possible explanations. (1) Threshold: secondary hosts are accepted less readily than primary hosts. (2) Feedback loop: insects ovipositing on primary hosts lay subsequent eggs faster than on secondary hosts. (3) Choice: insects compare plant cues sensed over a certain period and oviposit on preferred plants. We measured time and number of landings leading to egg-laying in a generalist moth, Helicoverpa punctigera, on a primary host and two secondary hosts and recorded subsequent egg-laying rates on each. The moths typically accepted only the primary host on the first landing and laid subsequent eggs on this host earlier in the night, indicating thresholds and feedback operate together.

Experience-dependent mushroom body plasticity in butterflies: consequences of search complexity and host range

An ovipositing insect experiences many sensory challenges during her search for a suitable host plant. These sensory challenges become exceedingly pronounced when host range increases, as larger varieties of sensory inputs have to be perceived and processed in the brain. Neural capacities can be exceeded upon information overload, inflicting costs on oviposition accuracy. One presumed generalist strategy to diminish information overload is the acquisition of a focused search during its lifetime based on experiences within the current environment, a strategy opposed to a more genetically determined focus expected to be seen in relative specialists. We hypothesized that a broader host range is positively correlated with mushroom body (MB) plasticity, a brain structure related to learning and memory. To test this hypothesis, butterflies with diverging host ranges (Polygonia c-album, Aglais io and Aglais urticae) were subjected to differential environmental complexities for oviposition, after which ontogenetic MB calyx volume differences were compared among species. We found that the relative generalist species exhibited remarkable plasticity in ontogenetic MB volumes; MB growth was differentially stimulated based on the complexity of the experienced environment. For relative specialists, MB volume was more canalized. All in all, this study strongly suggests an impact of host range on brain plasticity in Nymphalid butterflies.

Do Fruit Ripening Volatiles Enable Resource Specialism in Polyphagous Fruit Flies?

Frugivorous tephritid fruit flies have lineages with high levels of host generalism. These insects use olfaction to locate fruits, but how they are able to recognize the odors of so many different host species is poorly understood. We used a series of behavioral experiments to investigate the role of fruit ripening volatiles as host cues in the Queensland fruit fly, Bactrocera tryoni (Froggatt), a polyphagous pest in Australia. Odors of mature guava (Psidium guajava) attracted female and male flies more strongly than three other ripening stages and guava pulp. We analyzed volatiles from guava odor and selected eleven compounds, all of which elicited an electrophysiological response in the antenna of female flies. Three of these, ethyl acetate, ethyl butyrate, and ethyl propionate, were released at the highest rates from the most attractive ripening stage. In behavioral trials, these three esters were not attractive individually, whereas a combination was necessary and sufficient in attracting female flies. The three-component blend was as attractive as the entire 11-component blend, which without these key volatiles was not attractive. Moreover, injecting low ranking hosts (squash and cucumber) with the three volatiles increased attraction in ovipositing female flies. These fruit flies are classed as generalists, but like many polyphagous insects they could be regarded as resource specialists, preferring specific plant reproductive stages with predictable odor cues. Exploring olfaction from this perspective could improve our understanding of host choice in polyphagous insects, and the selection of volatiles to be used as attractants in insect pest management.

Butterfly oviposition preference is not related to larval performance on a polyploid herb

The preference–performance hypothesis predicts that female insects maximize their fitness by utilizing host plants which are associated with high larval performance. Still, studies with several insect species have failed to find a positive correlation between oviposition preference and larval performance. In the present study, we experimentally investigated the relationship between oviposition preferences and larval performance in the butterfly Anthocharis cardamines. Preferences were assessed using both cage experiments and field data on the proportion of host plant individuals utilized in natural populations. Larval performance was experimentally investigated using larvae descending from 419 oviposition events by 21 females on plants from 51 populations of two ploidy types of the perennial herb Cardamine pratensis. Neither ploidy type nor population identity influenced egg survival or larval development, but increased plant inflorescence size resulted in a larger final larval size. There was no correlation between female oviposition preference and egg survival or larval development under controlled conditions. Moreover, variation in larval performance among populations under controlled conditions was not correlated with the proportion of host plants utilized in the field. Lastly, first instar larvae added to plants rejected for oviposition by butterfly females during the preference experiment performed equally well as larvae growing on plants chosen for oviposition. The lack of a correlation between larval performance and oviposition preference for A. cardamines under both experimental and natural settings suggests that female host choice does not maximize the fitness of the individual offspring.

Host-Plant Specialization Mediates the Influence of Plant Abundance on Host Use by Flower Head-Feeding Insects

Among-population variation in host use is a common phenomenon in herbivorous insects. The simplest and most trivial explanation for such variation in host use is the among-site variation in plant species composition. Another aspect that can influence spatial variation in host use is the relative abundance of each host-plant species compared to all available hosts. Here, we used endophagous insects that develop in flower heads of Asteraceae species as a study system to investigate how plant abundance influences the pattern of host-plant use by herbivorous insects with distinct levels of host-range specialization. Only herbivores recorded on three or more host species were included in this study. In particular, we tested two related hypotheses: 1) plant abundance has a positive effect on the host-plant preference of herbivorous insects, and 2) the relative importance of plant abundance to host-plant preference is greater for herbivorous species that use a wider range of host-plant species. We analyzed 11 herbivore species in 20 remnants of Cerrado in Southeastern Brazil. For 8 out of 11 herbivore species, plant abundance had a positive influence on host use. In contrast to our expectation, both the most specialized and the most generalist herbivores showed a stronger positive effect of plant species abundance in host use. Thus, we found evidence that although the abundance of plant species is a major factor determining the preferential use of host plants, its relative importance is mediated by the host-range specialization of herbivores.

'Do you remember the first time?' Host plant preference in a moth is modulated by experiences during larval feeding and adult mating

In insects, like in other animals, experience-based modulation of preference, a form of phenotypic plasticity, is common in heterogeneous environments. However, the role of multiple fitness-relevant experiences on insect preference remains largely unexplored. For the multivoltine polyphagous moth Spodoptera littoralis we investigated effects of larval and adult experiences on subsequent reproductive behaviours. We demonstrate, for the first time in male and female insects, that mating experience on a plant modulates plant preference in subsequent reproductive behaviours, whereas exposure to the plant alone or plant together with sex pheromone does not affect this preference. When including larval feeding experiences, we found that both larval rearing and adult mating experiences modulate host plant preference. These findings represent the first evidence that host plant preferences in polyphagous insects are determined by a combination of innate preferences modulated by sensory feedback triggered by multiple rewarding experiences throughout their lifetime.

The spatial and temporal distributions of arthropods in forest canopies: uniting disparate patterns with hypotheses for specialisation

Arguably the majority of species on Earth utilise tropical rainforest canopies, and much progress has been made in describing arboreal assemblages, especially for arthropods. The most commonly described patterns for tropical rainforest insect communities are host specificity, spatial specialisation (predominantly vertical stratification), and temporal changes in abundance (seasonality and circadian rhythms). Here I review the recurrent results with respect to each of these patterns and discuss the evolutionary selective forces that have generated them in an attempt to unite these patterns in a holistic evolutionary framework. I propose that species can be quantified along a generalist-specialist scale not only with respect to host specificity, but also other spatial and temporal distribution patterns, where specialisation is a function of the extent of activity across space and time for particular species. When all of these distribution patterns are viewed through the paradigm of specialisation, hypotheses that have been proposed to explain the evolution of host specificity can also be applied to explain the generation and maintenance of other spatial and temporal distribution patterns. The main driver for most spatial and temporal distribution patterns is resource availability. Generally, the distribution of insects follows that of the resources they exploit, which are spatially stratified and vary temporally in availability. Physiological adaptations are primarily important for host specificity, where nutritional and chemical variation among host plants in particular, but also certain prey species and fungi, influence host range. Physiological tolerances of abiotic conditions are also important for explaining the spatial and temporal distributions of some insect species, especially in drier forest environments where desiccation is an ever-present threat. However, it is likely that for most species in moist tropical rainforests, abiotic conditions are valuable indicators of resource availability, rather than physiologically limiting factors. Overall, each distribution pattern is influenced by the same evolutionary forces, but at differing intensities. Consequently, each pattern is linked and not mutually exclusive of the other distribution patterns. Most studies have examined each of these patterns in isolation. Future work should focus on examining the evolutionary drivers of these patterns in concert. Only then can the relative strength of resource availability and distribution, host defensive phenotypes, and biotic and abiotic interactions on insect distribution patterns be determined.

Arabidopsis thaliana plants with different levels of aliphatic- and indolyl-glucosinolates affect host selection and performance of Bemisia tabaci

Generalist insects show reduced selectivity when subjected to similar, but not identical, host plant chemical signatures. Here, we produced transgenic Arabidopsis thaliana plants that over-express genes regulating the aliphatic- and indolyl- glucosinolates biosynthetic pathways with either a constitutive (CaMV 35S) or a phloem-specific promoter (AtSUC2). This allowed us to examine how exposure to high levels of aliphatic- or indolyl-glucosinolates in homogenous habitats (leaf cage apparatus containing two wild-type or two transgenic leaves) and heterogeneous habitats (leaf cage apparatus containing one wild-type and one transgenic leaf) affects host selection and performance of Bemsia tabaci, a generalist phloem-feeding insect. Data from homogenous habitats indicated that exposure to A. thaliana plants accumulating high levels of aliphatic- or indolyl-glucosinolates negatively affected the performance of both adult females and nymphs of B. tabaci. Data from heterogeneous habitats indicated that B. tabaci adult females selected for oviposition plants on which their offspring perform better (preference-performance relationship). However, the combinations of wild-type and transgenic plants in heterogeneous habitats increased the period of time until the first choice was made and led to increased movement rate on transgenic plants, and reduced fecundity on wild-type plants. Overall, our findings are consistent with the view that both performance and selectivity of B. tabaci decrease in heterogeneous habitats that contain plants with closely-related chemical signatures.

Adaptation to a novel host by a seed beetle (Coleoptera: Chrysomelidae: Bruchinae): effect of source population

Geographic populations of a widespread species can differ in their ability to adapt to a novel environment because they possess different amounts of the requisite genetic variation. We compared responses to the same novel host in ecologically and genetically divergent populations of the seed beetle Callosobruchus maculatus (F.). Populations from Africa and Asia had been derived from and maintained on different legume hosts. In preselection assays, both populations exhibited lower survival, slower development, and smaller size on a third host (adzuki bean), and the difference in performance between the ancestral and novel hosts was especially high for the African population. Replicate lines of each population were switched to adzuki bean or maintained on the ancestral host, and beetle performance was measured on both hosts after 12 generations. Survival on adzuki bean increased substantially in the adzuki-bean lines of the African population, but improved only slightly in the Asian lines. Similarly, only the African adzuki-bean lines exhibited significantly faster development on adzuki bean. Improved performance on adzuki bean did not simultaneously reduce performance on the ancestral host. Together with previous studies, these results confirm that populations of C. maculatus often possess sufficient standing genetic variation for rapid adaptation to a novel host, but the magnitude of the response may depend on the source population. Although international trade in grain legumes can expand beetle host ranges and produce unusual biotypes, the consistent absence of strong genetic trade-offs in larval performance or adult oviposition across hosts makes it unlikely that this insect would form distinct host races.

Choosing between good and better: optimal oviposition drives host plant selection when parents and offspring agree on best resources

Insect preferences for particular plant species might be subjected to trade-offs among several selective forces. Here, we evaluated, through laboratory and field experiments, the feeding and ovipositing preferences of the polyphagous leafminer Liriomyza huidobrensis (Diptera: Agromyzidae) in relation to adult and offspring performance and enemy-free space. Female leafminers preferred laying their eggs on Vicia faba (Fabaceae) over Beta vulgaris var. cicla (Chenopodiaceae), in both laboratory and field choice experiments, although no oviposition preference was observed in no-choice tests. Females fed more often on B. v. var. cicla (no-choice test) or showed no feeding preference (choice test), even when their realized fecundity was remarkably higher on V. faba. Offspring developed faster, tended to survive better, and attained bigger adult size on the preferred host plant. Also, a field experiment showed higher overall parasitism rates for leafminers developing on B. v. var. cicla, with a nonsignificant similar tendency in field surveys. According to these results, host plant selection by L. huidobrensis appears to be driven mainly by variation in host quality. Moreover, the consistent oviposition choices for the best host and the labile feeding preferences observed here, suggest that host plant selection might be driven by maximization of offspring fitness even without a conflict of interest between parents and offspring. Overall, these results highlight the complexity of decisions performed by phytophagous insects regarding their host plants, and the importance of simultaneous evaluation of the various driving forces involved, in order to unravel the adaptive significance of female choices.

Field observations of oviposition by a specialist herbivore on plant parts and plant species unsuitable as larval food

Where a female places her eggs can have a major impact on the fitness of her offspring, especially for insects in which the winged adults are far more mobile than the neonates. Larvae of Heliothis subflexa (Guenee) (Lepidoptera: Noctuidae), a specialist moth phylogenetically nested within a generalist clade, feed only on fruit of some Physalis species. Field observations of the oviposition behavior of H. subflexa revealed that 1) females laid most of their eggs on leaves of the Physalis plant, despite the larvae's frugivorous diet, and 2) females laid nearly 20% of the eggs on nonhost plant species. Most eggs oviposited on nonhosts were placed close to the host plant-88% were within 15 cm of the Physalis plant. However, in a study of neonate movement, we found that a distance of 2 cm from the hatch site to the host plant significantly decreased the ability of neonates to establish on the host plant. The estimated fitness cost, quantified as reduced neonate survival, for females ovipositing on nonhosts is 8-17%. Many ecological and evolutionary factors could result in oviposition on less suitable host parts and on nonhosts. One possibility is that specialization on Physalis has recently evolved in H. subflexa, and females have not fully optimized their oviposition behavior. However, the fitness cost of oviposition on nonhosts may be balanced by fitness benefits of such behavior, such as faster decision-making and reduced predation.

Increased plant volatile production affects oviposition, but not larval development, in the moth Helicoverpa armigera

It is well established that herbivorous insects respond to changes in plant odour production, but little attention has been given to whether these responses relate to direct fitness costs of plant volatile production on insect growth and survival. Here, we use transgenic Nicotiana tabacum (tobacco) plants that produce relatively large amounts of the volatile (S)-linalool to study whether the responses of egg-laying herbivorous insects to linalool production relate directly to the growth and survival of offspring. In choice tests, fewer eggs were laid on transgenic plants compared with non-transformed controls, indicating that increased linalool emissions have a deterrent effect on Helicoverpa armigera oviposition. Larval survival and larval mass after feeding on transgenic leaves, however, was comparable to non-transformed controls. (S)-linalool, whether in volatile or sequestered form, does not appear to have a direct effect on offspring fitness in this moth. We discuss how the ecology of this polyphagous moth species may necessitate a high tolerance for certain volatiles and their related non-volatile compounds, and suggest that responses by adult female H. armigera moths towards increased linalool production may be context specific and relate to other indirect effects on fitness.

Odour maps in the brain of butterflies with divergent host-plant preferences

Butterflies are believed to use mainly visual cues when searching for food and oviposition sites despite that their olfactory system is morphologically similar to their nocturnal relatives, the moths. The olfactory ability in butterflies has, however, not been thoroughly investigated. Therefore, we performed the first study of odour representation in the primary olfactory centre, the antennal lobes, of butterflies. Host plant range is highly variable within the butterfly family Nymphalidae, with extreme specialists and wide generalists found even among closely related species. Here we measured odour evoked Ca²⁺ activity in the antennal lobes of two nymphalid species with diverging host plant preferences, the specialist Aglais urticae and the generalist Polygonia c-album. The butterflies responded with stimulus-specific combinations of activated glomeruli to single plant-related compounds and to extracts of host and non-host plants. In general, responses were similar between the species. However, the specialist A. urticae responded more specifically to its preferred host plant, stinging nettle, than P. c-album. In addition, we found a species-specific difference both in correlation between responses to two common green leaf volatiles and the sensitivity to these compounds. Our results indicate that these butterflies have the ability to detect and to discriminate between different plant-related odorants.

Trade-offs of host use between generalist and specialist Helicoverpa sibling species: adult oviposition and larval performance

Much attention has been paid to the question of the relative importance of female behaviour versus larval feeding capacities in determining the host range of herbivorous insects. Host-use trade-offs displayed by generalist and specialist sister species of the genus Helicoverpa were evaluated to examine the relationship between maternal choice and offspring performance. The prediction of optimal oviposition theory, that females will choose to lay eggs on plants on which their offspring perform best as larvae, was tested by measuring oviposition preference and larval performance of Helicoverpa armigera and H. assulta on tobacco, sunflower, and hot pepper. These two measures were more highly correlated in the specialist H. assulta. Both species exhibited the same oviposition preference ranking: tobacco > sunflower > hot pepper. H. armigera larvae preferred sunflower, followed by tobacco and hot pepper; while H. assulta larvae preferred tobacco to sunflower and hot pepper, consistent with their mothers' oviposition preference. Duration of the total period from egg to adult emergence for each species was significantly shorter on the host plant preferred by the larvae. H. assulta had shorter larval duration and higher relative growth rate than H. armigera on tobacco and hot pepper, and vice versa for sunflower, indicating species differences in host utilization. Thus, while only the specialist H. assulta displayed the predicted optimal oviposition pattern, females of both species show the least preference for the plant on which their offspring perform worst. Selection for optimal oviposition may be stronger on the specialist, which has fewer choices and lower lifetime fecundity than the generalist.

A meta-analysis of preference-performance relationships in phytophagous insects

The extent to which behavioural choices reflect fine-tuned evolutionary adaptation remains an open debate. For herbivorous insects, the preference-performance hypothesis (PPH) states that female insects will evolve to oviposit on hosts on which their offspring fare best. In this study, we use meta-analysis to assess the balance of evidence for and against the PPH, and to evaluate the role of individual factors proposed to influence host selection by female insects. We do so in an explicitly bitrophic context (herbivores versus plants). Overall, our analyses offer clear support for the PPH: Offspring survive better on preferred plant types, and females lay more eggs on plant types conducive to offspring performance. We also found evidence for an effect of diet breadth on host choice: female preference for 'good quality plants' was stronger in oligophagous insects than in polyphagous insects. Nonetheless, despite the large numbers of preference-performance studies conducted to date, sample sizes in our meta-analysis are low due to the inconsistent format used by authors to present their results. To improve the situation, we invite authors to contribute to the data base emerging from this work, with the aim of reaching a strengthened synthesis of the subject field.

Attraction of Dibrachys cavus (Hymenoptera: Pteromalidae) to its Host Frass Volatiles

The European grapevine moth, Lobesia botrana (Lepidoptera: Tortricidae), is a polyphagous insect able to develop on grapes and wild plants. We tested the hypothesis that the parasitoid Dibrachys cavus (Hymenoptera: Pteromalidae) uses the larval frass in its host search. A two-armed olfactometer was used to measure the attractiveness of L. botrana larvae, their silk, or their frass after larvae were fed on different host plants. Frass of three Lepidoptera (L. botrana, Eupoecillia ambiguella, Sphinx ligustri) and one Orthoptera (Chorthippus brunneus) was assayed, but only L. botrana was used to test an effect of the larval host plant (two grape cultivars and three other plant species) to D. cavus females. Larvae without frass did not attract D. cavus whatever their origin, but their frass was attractive at a dose of 2-3 days equivalent of larval frass production. The silk produced by a single larva (L. botrana) was not attractive to D. cavus. The parasitoid was most attracted to the odor of S. ligustri; the frass of L. botrana was more attractive than that of E. ambiguella, irrespective of the species on which D. cavus had been reared. There was no difference in attractiveness of frass collected from L. botrana raised on food containing different plants. Chemical extracts using five different polarity solvents (acetone, dichloromethane, hexane, methanol, and water) differed in attractiveness to D. cavus. Water and dichloromethane were the most attractive. This suggests that a complex volatile signal made from intermediate to polar volatiles may be involved in attraction. D. cavus used frass to discriminate between different potential host species. Our results revealed that the larval food of L. botrana did not modify frass attractiveness, but that the moth species did.

Individual advantages to ecological specialization: insights on cognitive constraints from three conspecific taxa

The information-processing hypothesis (IPH) posits that specialist herbivores should make host-associated decisions more effectively than generalists and thus enjoy associated fitness advantages that may help explain the evolutionary prevalence of host-specific insects. This is because generalists must evaluate a greater diversity of host plants/cues than specialists and thus face a cognitive challenge that is predicted to constrain the efficiency and accuracy of their choices. Here, we present the first individual-level evaluation of this hypothesis. This involved experimentally quantifying the specificity, efficiency, and accuracy of host selection, as both larvae and adults, for many individuals representing each of three 'host forms' of Neochlamisus bebbianae leaf beetles. These experiments provided several significant findings: host forms differed in larval specificity, with the more specialized host forms more efficiently and accurately selecting optimal hosts as both larvae and adults. Positive correlations between larval specificity and both efficiency and accuracy across test individuals provided the most direct evidence to date for a biological association between these variables. Our results thus provide strong and consistent support for the IPH at the level of both populations and individuals. Because individual N. bebbianae make many host-associated decisions in nature, our results suggest that cognitive constraints may play a major role in the evolutionary dynamics of ongoing ecological specialization and diversification in this species.

Is more choice always desirable? Evidence and arguments from leks, food selection, and environmental enrichment

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 Tetrao tetrix 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. Operant experiments that demonstrate mild preferences for free choice concern choice about the means to get food rather than the food itself. 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.