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Intra-genotypic variability (IGV) occurs when individuals with the same genotype, raised in the same environment and then tested under the same conditions, express different trait values. Game theoretical and bet-hedging models have suggested two ways that a single genotype might generate variable behaviour when behavioural variation is discrete rather than continuous: behavioural polyphenism (a genotype produces different types of individuals, each of which consistently expresses a different type of behaviour) or stochastic variability (a genotype produces one type of individual who randomly expresses different types of behaviour over time). We first demonstrated significant differences across 14 natural genotypes of male Drosophila melanogaster in the variability (as measured by entropy) of their microhabitat choice, in an experiment in which each fly was allowed free access to four different types of habitat. We then tested four hypotheses about ways that within-individual variability might contribute to differences across genotypes in the variability of microhabitat choice. There was no empirical support for three hypotheses (behavioural polymorphism, consistent choice, or time-based choice), nor could our results be attributed to genotypic differences in activity levels. The stochastic variability hypothesis accurately predicted the slope and the intercept of the relationship across genotypes between entropy at the individual level and entropy at the genotype level. However, our initial version of the stochastic model slightly but significantly overestimated the values of individual entropy for each genotype, pointing to specific assumptions of this model that might need to be adjusted in future studies of the IGV of microhabitat choice. This is among a handful of recent studies to document genotypic differences in behavioural IGV, and the first to explore ways that genotypic differences in within-individual variability might contribute to differences among genotypes in the predictability of their behaviour.

Mixed-species groups describe active associations among individuals of 2 or more species at the same trophic level. Mixed-species groups are important to key ecological and evolutionary processes such as competition and predation, and research that ignores the presence of other species risks ignoring a key aspect of the environment in which social behavior is expressed and selected. Despite the defining emphasis of active formation for mixed-species groups, surprisingly little is known about the mechanisms by which mixed-species groups form. Furthermore, insects have been almost completely ignored in the study of mixed-species groups, despite their taxonomic importance and relative prominence in the study of single-species groups. Here, we measured group formation processes in Drosophila melanogaster and its sister species, Drosophila simulans. Each species was studied alone, and together, and one population of D. melanogaster was also studied both alone and with another, phenotypically distinct D. melanogaster population, in a nested-factorial design. This approach differs from typical methods of studying mixed-species groups in that we could quantitatively compare group formation between single-population, mixed-population, and mixed-species treatments. Surprisingly, we found no differences between treatments in the number, size, or composition of groups that formed, suggesting that single- and mixed-species groups form through similar mechanisms of active attraction. However, we found that mixed-species groups showed elevated interspecies male–male interactions, relative to interpopulation or intergenotype interactions in single-species groups. Our findings expand the conceptual and taxonomic study of mixed-species groups while raising new questions about the mechanisms of group formation broadly. [ABSTRACT FROM AUTHOR]

Sex differences in disease susceptibility are widespread, and these disparities are often compounded in cases where sexual dimorphism increases exposure risk to parasites for one sex more than the other. Studies rarely link sex differences in disease susceptibility to sex differences in infection avoidance behavior. Yet, understanding the intersection of hosts' susceptibility to infection and infection avoidance behavior is essential to predicting infection risk variation. Here, we use the fruit fly Drosophila melanogaster and a generalist entomopathogenic fungus, Metarhizium robertsii, which can be transmitted directly, indirectly, and post‐mortem as a model host–pathogen system. We test whether the relationship between susceptibility to infection and pathogen avoidance behavior covaries with host sex. We first measured differences in resistance between male and female flies after three different types of exposure—direct, sexual, and environmental—to infectious fungal conidiospores. Then, we tested whether male and female flies differed in the likelihood of mating with infected partners and their avoidance of food patches with increased infection risk. Females were more susceptible to infection under all three exposure techniques. When confronted with an infectious partner, females mated sooner than males. However, when given a choice between an exposed partner and an unexposed partner, females take longer to begin copulating compared with males, though neither sex was more likely to choose the unexposed partner than expected by chance. Neither male nor females flies avoided food patches containing infectious conidiospores, though only females show an aversion to food sites containing an infectious fly corpse. These experiments suggest that sex differences in disease susceptibility may be counteracted via differential pathogen avoidance behavior, though the strength of avoidance behavior appears to vary across different contexts of infection risk. [ABSTRACT FROM AUTHOR]

Decision making is involved in many behaviors contributing to fitness, such as habitat choice, mate selection, and foraging. Because of this, high decision-making accuracy (i.e., selecting the option most beneficial for fitness) should be under strong selection. However, decision making is energetically costly, often involving substantial time and energy to survey the environment to obtain high-quality information. Thus, for high decision making accuracy to evolve, its benefits should outweigh its costs. Inconsistency in the net benefits of decision making across environments is hypothesized to be an important means for maintaining variation in this trait. However, very little is known about how environmental factors influence the evolution of decision making to produce variation among individuals, genotypes, and species. Here, we compared two recently diverged species of Drosophila differing substantially in habitat breadth and degree of environmental predictability and variability: Drosophilasechellia and Drosophilasimulans. We found that the species evolving under higher environmental unpredictability and variability showed higher decision-making accuracy, but not higher environmental sampling. [ABSTRACT FROM AUTHOR]

There is growing interest in individual variation in non-human animals. Research in this area from an evolutionary and ecological perspective seeks to understand the forces that generate and maintain consistent individual differences in behavior. There are both important points of contact and differences between research on non-human animals and the framework for studying human personality in Baumert and colleagues' article. In particular, we argue that the study of individual variation in both humans and non-human animals can benefit from further consideration of the ways in which our subjects influence their environments. [ABSTRACT FROM AUTHOR]