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Evolution has shaped social dynamics across species to resolve aggressive interactions with as little physical fighting as possible, balancing the potential value of the resources gained against the cost of suffering injury or death (Holekamp & Strauss, 2016;Maynard Smith & Harper, 1988;van Staaden et al., 2011). Aggressive behavior, through either physical or non-physical acts, is used to resolve conflicts related to access to resources such as food, shelter, territory, and mates. Extraordinary diversity exists in how different species express aggression. For example, body size is a reliable predictor of contest intensity in fish relying on visual displays (Moretz, 2003;Reddon et al., 2011), whereas in frogs, in which displays are primarily auditory, body size is generally unrelated to the duration or escalation of aggressive interactions (Owen & Gordon, 2005; Reichert & Gerhardt, 2011). Even members of the same species alter

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32Our understanding of how the design of peripheral sensory structures is coupled with neural 33 processing capacity to adaptively support division of labor is limited. Workers of the remarkably 34 polymorphic fungus-growing ant Atta cephalotes are behaviorally specialized by size: the 35 smallest workers (minims) tend fungi in dark subterranean chambers while larger workers 36 perform tasks mainly outside the nest. These strong differences in worksite light conditions are 37 predicted to influence sensory and processing requirements for vision. We found that eye 38 structure and visual neuropils have been be selected to maximize task performance according to 39 light availability. Minim eyes had few ommatidia, large interommatidial angles and eye 40 parameter values, suggesting selection for visual sensitivity over acuity. Large workers had 41 larger eyes with disproportionally more and larger ommatidia, and smaller interommatidial 42 angles and eye parameter values, reflecting peripheral sensory adaptation to ambient rainforest 43 light. Additionally, optic lobe and mushroom body collar volumes were disproportionately small 44 in minims, and within the optic lobe, lamina and lobula relative volumes increased with worker 45 size whereas the medulla decreased. Visual system phenotypes thus correspond to task 46 specializations in dark or light environments and reflect a functional neuroplasticity 47 underpinning division of labor in this socially complex agricultural ant. 48 49

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This study examines the distribution and invasion dynamics of Wolbachia in a recently established Formica fusca population. Preliminary data revealed the intermittent infection of Wolbachia across colonies, providing the opportunity to test for ecological factors affecting the acquisition and spread of the parasite. Only 35% of colonies are infected in this population. Both infected and noninfected nests have similar dispersion patterns that approximate a random distribution, suggesting that transmission of Wolbachia between adjacent colonies is not common. There is no difference in the infection rate between workers and brood, indicating that workers are not actively eliminating the infection. Our results show no significant association between Wolbachia infection and nest size; however, infected colonies tend to be larger than noninfected colonies. Finally, Wolbachia infection was not associated with queen number. Overall, our results suggest no large fitness differences between infected and noninfected colonies, although small fitness effects cannot be ruled out for this population.

Steroid hormones play numerous important and diverse roles in the differentiation and development of vertebrate primary and secondary reproductive characteristics. However, the exact role of androgen receptors (ARs)-which bind circulating androgens-in this regulatory pathway is unclear. Teleost fishes further complicate this question by having two paralogs of AR (ARα and ARβ) resulting from a duplication of their ancestral genome. We investigated the functional role of these two ARs on testes growth and development by experimentally eliminating receptor function of one or both paralogs using CRISPR/Cas9 genome edited Astatotilapia burtoni, an African cichlid fish. Fish with two or more functional receptor alleles were more likely to be male compared to fish with one or fewer, suggesting that the two paralogs of the receptor may be redundant in regulating early sex determination. In contrast, we found that adult testes size was significantly affected by distinct combinations of mutant and wild-type AR alleles. We present a working model whereby ARβ facilitates testes growth and ARα causes testes regression. This mechanism may contribute to the robust social and physiological plasticity displayed by A. burtoni and other social teleost fish.

Teleost fishes have emerged as tractable models for studying the neuroendocrine regulation of social behavior via molecular genetic techniques, such as CRISPR/Cas9 gene editing. Moreover, teleosts provide an opportunity to investigate the evolution of steroid receptors and their functions, as species within this lineage possess novel steroid receptor paralogs that resulted from a teleost-specific whole genome duplication. Although teleost fishes have grown in popularity as models for behavioral neuroendocrinology, there is not a consistent nomenclature system for steroid receptors and their genes, which may impede a clear understanding of steroid receptor paralogs and their functions. Here, we used a phylogenetic approach to assess the relatedness of protein sequences encoding steroid receptor paralogs in 18 species from 12 different orders of the Infraclass Teleostei. While most similarly named sequences grouped based on the established phylogeny of the teleost fish lineage, our analysis revealed several inconsistencies in the nomenclature of steroid receptor paralogs, particularly for sequences encoding estrogen receptor beta (ERβ) and estrogen-related receptor gamma (ERγ). Based on our results, we propose a nomenclature system for teleosts in which Greek symbols refer to proteins and numbers refer to genes encoding different subtypes of steroid receptors within the five major groups of this nuclear receptor subfamily. Collectively, our results bridge a critical gap by providing a cohesive naming system for steroid receptors in teleost fishes, which will serve to improve communication, promote collaboration, and enhance our understanding of the evolution and function of steroid receptors across vertebrates.