Multilevel selection on social network traits differs between sexes in experimental populations of forked fungus beetles

Both individual and group behavior can influence individual fitness, but multilevel selection is rarely quantified on social behaviors. Social networks provide a unique opportunity to study multilevel selection on social behaviors, as they describe complex social traits and patterns of interaction at both the individual and group levels. In this study, we used contextual analysis to measure the consequences of both individual network position and group network structure on individual fitness in experimental populations of forked fungus beetles (Bolitotherus cornutus) with two different resource distributions. We found that males with high individual connectivity (strength) and centrality (betweenness) had higher mating success. However, group network structure did not influence their mating success. Conversely, we found that individual network position had no effect on female reproductive success but that females in populations with many social interactions experienced lower reproductive success. The strength of individual-level selection in males and group-level selection in females intensified when resources were clumped together, showing that habitat structure influences multilevel selection. Individual and emergent group social behavior both influence variation in components of individual fitness but impact male mating success and female reproductive success differently, setting up intersexual conflicts over patterns of social interactions at multiple levels.

Methods
These data describe patterns of social interaction in 12 experimental populations of Bolitotherus cornutus. Each population experienced both a clumped and an even distribution of bracket fungi resources over two different three-week observation periods (i.e. the resource distribution was switched between observation periods). Social interactions were defined as individuals in close proximity (within 5cm) of one another and were collected through scan sampling three times a day. Fitness metrics (mate guarding in males and egg laying in females) were also documented during behavioral observations. Behavioral datasets were error-checked to remove all unidentifiable beetles and all impossible or partially recorded interactions. Weighted individual and group social network metrics were calculated from observed social interactions using the simple ratio index. Network density was calculated in the R package sna. All other weighted social network metrics were calculated in the R package tnet.