A major challenge in evolutionary biology is to understand the origin and maintenance ofcomplex animal societies. Identifying the mechanisms involved in transitions from solitary togroup living can shed light on the evolutionary processes through which sociality arises. Bees area valuable group for studying social evolution because the common ancestor of all bees wassolitary and the most extreme form of group living, eusociality, has evolved multipleindependent times within the bees. Recent advances in genome sequencing and analysistechnologies have opened up new research avenues for large-scale studies of molecular functionand evolution in non-model species and I apply these new methods to the study of socialevolution in bees and other social insects. In Chapter 1, I provide a detailed overview of theresearch included in this dissertation. Chapters 2 and 3 are aimed at identifying genetic changesassociated with social evolution in insects. In Chapter 2, I review and synthesize currentdevelopments in molecular evolutionary analyses of social evolution in bees, wasps, ants andtermites. In Chapter 3, I use comparative genomics to search for genes involved in convergentevolution of sociality using new genomic resources I developed for a set of 10 socially diversebee species. This study identifies genes and biological processes that are evolving more rapidlyin eusocial relative to non-eusocial lineages across three independent origins of eusociality.Chapters 4 and 5 focus on features of solitary bee development and behavior that may havefacilitated the evolution of bee sociality. For this work, I developed genomic resources andexperimental methods for a new model for the solitary ancestor of social bees, the alfalfaleafcutting bee Megachile rotundata. In Chapter 4, I test the hypothesis that social insect castesevolved from an ancestral groundplan regulating the expression of larval diapause. I found thatthe main regulator of caste determination, larval nutrition, also regulates diapause plasticity in M. rotundata. Additionally, orthologs many of the genes that respond to nutritional manipulation inM. rotundata larvae are also involved in social bee caste determination. Moreover, royal jelly,the honey bee caste-determining substance, was able to induce diapause in M. rotundata andaffects the expression of genes involved in DNA methylation just as it does in honey bees. I alsoshow that larval nutrition can cause variation in M. rotundata female reproductive behaviorunder environmental conditions that may favor the evolution of sociality. Chapter 5 usescomparative transcriptomics to investigate how molecular mechanisms involved in eusocialbehaviors may have evolved from a solitary ancestor. I collected brain gene expression profilesfrom M. rotundata associated with nesting phase and mating status. Nesting phase affects theexpression of hundreds of genes while mating status affects very few genes. Orthologs of manyof the genes associated with M. rotundata nesting phase have previously been shown to beassociated with maturation, reproductive status, and brood care in eusocial bees and wasps,suggesting that these shared genes may have been involved in eusocial evolution. The work inthis dissertation leverages the power of new genomic technologies and uses a comparativeapproach to provide new insights into mechanisms of social evolution.
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