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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

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.

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Current methods used to quantify brain size and compartmental scaling relationships in studies of social insect brain evolution involve manual annotations of images from histological samples, confocal microscopy or other sources. This process is susceptible to human bias and error and requires time-consuming effort by expert annotators. Standardized brain atlases, constructed through 3D registration and automatic segmentation, surmount these issues while increasing throughput to robustly sample diverse morphological and behavioral phenotypes. Here we design and evaluate three strategies to construct statistical brain atlases, or templates, using ants as a model taxon. The first technique creates a template by registering multiple brains of the same species. Brain regions are manually annotated on the template, and the labels are transformed back to each individual brain to obtain an automatic annotation, or to any other brain aligned with the template. The second strategy also creates a template from multiple brain images but obtains labels as a consensus from multiple manual annotations of individual brains comprising the template. The third technique is based on a template comprising brains from multiple species and the consensus of their labels. We used volume similarity as a metric to evaluate the automatic segmentation produced by each method against the inter- and intra-individual variability of human expert annotators. We found that automatic and manual methods are equivalent in volume accuracy, making the template technique an extraordinary tool to accelerate data collection and reduce human bias in the study of the evolutionary neurobiology of ants and other insects.

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.