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Abstract Social group structure is highly variable and can be important for nearly every aspect of behavior and its fitness consequences. Group structure can be modeled using social network analysis, but we know little about the evolutionary factors shaping and maintaining variation in how individuals are embedded within their networks (i.e., network position). While network position is a pervasive target of selection, it remains unclear whether network position is heritable and can respond to selection. Furthermore, it is unclear how environmental factors interact with genotypic effects on network positions, or how environmental factors shape selection on heritable network structure. Here we show multiple measures of social network position are heritable, using replicate genotypes and replicate social groups ofDrosophila melanogasterflies. Our results indicate genotypic differences in network position are largely robust to changes in the environment flies experience, though some measures of network position do vary across environments. We also show selection on multiple network position metrics depends on the environmental context they are expressed in, laying the groundwork for better understanding how spatio-temporal variation in selection contributes to the evolution of variable social group structure. 

Evolutionary feedbacks occur when evolution in one generation alters the environment experienced by subsequent generations and are an expected result of indirect genetic effects (IGEs). Hypotheses abound for the role of evolutionary feedbacks in climate change, agriculture, community dynamics, population persistence, social interactions, the genetic basis of evolution, and more, but evolutionary feedbacks have rarely been directly measured experimentally, leaving open questions about how feedbacks influence evolution. Using experimental evolution, we manipulated the social environment in which aggression was expressed and selected in fruit fly (Drosophila melanogaster) populations to allow or limit feedbacks. We selected for increased male–male aggression while allowing either positive, negative, or no feedbacks, alongside unselected controls. We show that populations undergoing negative feedbacks had the weakest evolutionary changes in aggression, while populations undergoing positive evolutionary feedbacks evolved supernormal aggression. Further, the underlying social dynamics evolved only in the negative feedbacks treatment. Our results demonstrate that IGE-mediated evolutionary feedbacks can alter the rate and pattern of behavioral evolution. 

Social behaviors can be influenced by the genotypes of interacting individuals through indirect genetic effects (IGEs) and can also display developmental plasticity. We investigated how develop- mental IGEs, which describe the effects of a prior social partner’s geno- type on later behavior, can influence aggression in male Drosophila melanogaster. We predicted that developmental IGEs cannot be esti- mated by simply extending the effects of contextual IGEs over time and instead have their own unique effects on behavior. On day 1 of the ex- periment, we measured aggressive behavior in 15 genotypic pairings (n p 600 males). On day 2, each of the males was paired with a new opponent, and aggressive behavior was again measured. We found con- textual IGEs on day 1 of the experiment and developmental IGEs on day 2 of the experiment: the influence of the day 1 partner’s genotype on the focal individual’s day 2 behavior depended on the genotypic iden- tity of both the day 1 partner and the focal male. Importantly, the devel- opmental IGEs in our system produced fundamentally different dynam- ics than the contextual IGEs, as the presence of IGEs was altered over time. These findings represent some of the first empirical evidence dem- onstrating developmental IGEs, a first step toward incorporating de- velopmental IGEs into our understanding of behavioral evolution. 

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’. 

Abstract 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.