The genetic basis of behavioral variation in the pharaoh ant
Walsh, Walsh , Linksvayer
Department of Biology, University of Pennsylvania; Department of Biology, University of Pennsylvania ; Department of Biology, University of Pennsylvania
A major goal of biology is to understand the molecular underpinnings and evolution of complex traits, such as behavior. Over the past 20 years, the study of behavior has largely focused on repeatable, inter-individual variation in behavior (i.e. animal personality). To better understand the evolution of behavioral variation and how it is maintained in populations, we must increase our understanding of its genetic basis. To achieve this goal, we used our unique heterogeneous stock population of pharaoh ant (Monomorium pharaonis) colonies, derived from eight initial lineages that have been systematically crossed over the past 10 years. This heterogeneous stock approach has been used to successfully map the genetic basis of many complex traits in mice and fruit flies. First, we measured aggression, foraging, and exploration of 243 pharaoh ant colonies and found that colonies exhibit consistent behavioral differences. We also measured a number of additional complex phenotypes, including worker, gyne, and male body size, colony caste and sex ratio, and cuticular hydrocarbon profile. We found that many of the measured phenotypes were correlated with each other and also with colony fitness, suggesting that natural selection is acting on these traits. Next, we used an animal model approach to estimate the heritability of all measured phenotypes. All phenotypes exhibited heritability estimates greater than zero. Furthermore, we genotyped pools of workers from each colony using restriction-site associated DNA sequencing. To identify quantitative trait loci (QTL) underlying the measured phenotypes, we performed a novel multimarker approach that combines chromosome partitioning, QTL mapping, and genome-wide association study. Overall, this study greatly increases our understanding of the biological basis of behavior and other complex traits and begins to fill the missing genetic component of animal personality research.