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Learning is central to our understanding of how behaviour is shaped by the environment. A key open question is whether learning across contexts evolves as an integrated process, or whether learning in each context is free to evolve separately. Here, we measured learning in two sensory contexts in multiple genotypes and both sexes of two closely related, but ecologically divergent, species of fruit flies, Drosophila simulans and Drosophila sechellia. These species are morphologically very similar but differ dramatically in ecology and population biology. We tested how flies from each genotype, sex and species responded to and learned about different gustatory and visual cues. This approach allowed us to test whether species differences in learning were independent or correlated across contexts. Surprisingly, we found no evidence that D. simulans learned in any of our treatments. In contrast, D. sechellia learned to avoid gustatory stimuli that were paired with an aversive stimulus, as predicted, but unexpectedly learned to approach visual stimuli that were paired with the aversive stimulus. At the genotype level, genotypes, but not species, differed in their naïve responses to stimuli, but genotypes did not differ in learning in either species. Our results demonstrate that D. sechellia indeed differs from D. simulans in both learning contexts, but in a stimulus-dependent way. We suggest that studies of additional species or population pairs that employ this framework will be critical for evaluating the dimensionality of learning and its evolution. 

Despite continued interest in mixed-species groups, we still lack a unified understanding of how ecological and social processes work across scales to influence group formation. Recent work has revealed ecological correlates of mixed-species group formation, but the mechanisms by which concomitant social dynamics produce these patterns, if at all, is unknown. Here, we use camera trap data for six mammalian grazer species in Serengeti National Park. Building on previous work, we found that ecological variables, and especially forage quality, influenced the chances of species overlap over small spatio-temporal scales (i.e. on the scales of several metres and hours). Migratory species (gazelle, wildebeest and zebra) were more likely to have heterospecific partners available in sites with higher forage quality, but the opposite was true for resident species (buffalo, hartebeest and topi). These findings illuminate the circumstances under which mixed-species group formation is even possible. Next, we found that greater heterospecific availability was associated with an increased probability of mixed-species group formation in gazelle, hartebeest, wildebeest and zebra, but ecological variables did not further shape these patterns. Overall, our results are consistent with a model whereby ecological and social drivers of group formation are species-specific and operate on different spatio-temporal scales. This article is part of the theme issue ‘Mixed-species groups and aggregations: shaping ecological and behavioural patterns and processes’. 

The position an individual holds in a social network is dependent on both its direct and indirect social interactions. Because social network position is dependent on the actions and interactions of conspecifics, it is likely that the genotypic composition of individuals within a social group impacts individuals' network positions. However, we know very little about whether social network positions have a genetic basis, and even less about how the genotypic makeup of a social group impacts network positions and structure. With ample evidence indicating that network positions influence various fitness metrics, studying how direct and indirect genetic effects shape network positions is crucial for furthering our understanding of how the social environment can respond to selection and evolve. Using replicate genotypes of Drosophila melanogaster fruit flies, we created social groups that varied in their genotypic makeup. Social groups were videoed, and networks were generated using motion-tracking software. We found that both an individual's own genotype and the genotypes of conspecifics in its social group affect its position within a social network. These findings provide an early example of how indirect genetic effects and social network theory can be linked, and shed new light on how quantitative genetic variation shapes the structure of social groups. This article is part of a discussion meeting issue ‘Collective behaviour through time’.