Date of Award
Program or Major
Doctor of Philosophy
Sandra M Rehan
Bees are highly charismatic and ecologically valuable organisms, and most popularly represented by the honey bee. Honey bees are well known in no small part because they are eusocial: a single reproductive queen continually lays eggs, and is supported by overlapping generations of thousands of non-reproductive workers, all performing specialized tasks to feed and protect the colony. Despite the ecological edge it seems to confer, eusociality has emerged in relatively few bee lineages; most have instead either remained solitary (the ancestral state for all bees) or demonstrate any of a range of less derived forms of social organization. Researchers have for decades been steadily teasing out the ecological, developmental, and evolutionary factors that may drive the emergence and elaboration of insect social complexity. This dissertation aims to join that effort by offering a handful of additional insights emerging from empirical testing of major social evolutionary hypotheses in bees of facultative and early sociality. My introductory Chapter 1 elaborates on the question of eusociality in greater detail and lays out the major social evolutionary hypotheses and their syntheses. I argue in support of research among bees of early or facultative sociality as systems in which much-needed empirical testing of evolutionary theory may be performed. In Chapter 2, I use relatedness and demographic data to calculate the inclusive fitness costs and benefits of social nesting in the small carpenter bee (Ceratina calcarata) which may rear a single worker-like daughter to aid in brood care. I find that social nesting may be advantageous to social nest mothers rather than daughters in this species, contrary to the expectations of kin selection theory. In Chapter 3, I further investigate sociality in C. calcarata using brain transcriptomic data that captures patterns of cis-regulation and gene expression associated with female maturation and two well-defined behavioral states, foraging and guarding, concurrently demonstrated by mothers and daughters in social nests. I find that the early social nest environment may have a strong effect on gene expression; and reveal foraging and guarding behaviors to be underpinned by deeply conserved genes that are differentially expressed within a highly modular gene network. In Chapter 4, I draw on another set of brain transcriptomic data, this time reflecting first and second year solitary females, queens, and workers of the long-lived and facultatively eusocial small carpenter bee, Ceratina japonica. I find that queen and worker phenotypes are underpinned by highly divergent gene regulatory pathways. I also show how genes underlying C. japonica’s queens and workers are well-conserved and demonstrate strikingly similar patterns of expression in other bees of early eusociality. I also discover that while the social nest environment may induce some shared shifts in lifetime gene expression among queens and workers vs solitary females, the role of oxidative damage reduction may be a proximate mechanism of prolonged longevity regardless of social phenotype. Appendix A details my development of polymorphic microsatellite markers using the C. calcarata genome, which were used in Chapter 2 of this dissertation and are now a publicly available tool for further research; the remaining Appendices provide mainly supplementary methods and figures for Chapters 3 and 4.
Shell, Wyatt Abram, "Behavioral and Genetic Mechanisms of Social Evolution: Insights from Incipiently and Facultatively Social Bees" (2020). Doctoral Dissertations. 2555.