Mechanisms involved in eusocial evolution in bees

Fischman, Brielle

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Description

Title

Mechanisms involved in eusocial evolution in bees

Author(s)

Fischman, Brielle

Issue Date

2014-01-16T18:18:11Z

Director of Research (if dissertation) or Advisor (if thesis)

Robinson, Gene E.

Doctoral Committee Chair(s)

Robinson, Gene E.

Committee Member(s)

• Fuller, Rebecca C.
• Hudson, Matthew E.
• Suarez, Andrew V.

Department of Study

School of Integrative Biology

Discipline

Biology

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• eusocial insects
• bees
• Megachile rotundata
• behavior
• social evolution
• molecular evolution
• genomics
• gene expression

Abstract

A major challenge in evolutionary biology is to understand the origin and maintenance of complex animal societies. Identifying the mechanisms involved in transitions from solitary to group living can shed light on the evolutionary processes through which sociality arises. Bees are a valuable group for studying social evolution because the common ancestor of all bees was solitary and the most extreme form of group living, eusociality, has evolved multiple independent times within the bees. Recent advances in genome sequencing and analysis technologies have opened up new research avenues for large-scale studies of molecular function and evolution in non-model species and I apply these new methods to the study of social evolution in bees and other social insects. In Chapter 1, I provide a detailed overview of the research included in this dissertation. Chapters 2 and 3 are aimed at identifying genetic changes associated with social evolution in insects. In Chapter 2, I review and synthesize current developments in molecular evolutionary analyses of social evolution in bees, wasps, ants and termites. In Chapter 3, I use comparative genomics to search for genes involved in convergent evolution of sociality using new genomic resources I developed for a set of 10 socially diverse bee species. This study identifies genes and biological processes that are evolving more rapidly in 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 have facilitated the evolution of bee sociality. For this work, I developed genomic resources and experimental methods for a new model for the solitary ancestor of social bees, the alfalfa leafcutting bee Megachile rotundata. In Chapter 4, I test the hypothesis that social insect castes evolved from an ancestral groundplan regulating the expression of larval diapause. I found that the 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 in M. 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 and affects the expression of genes involved in DNA methylation just as it does in honey bees. I also show that larval nutrition can cause variation in M. rotundata female reproductive behavior under environmental conditions that may favor the evolution of sociality. Chapter 5 uses comparative transcriptomics to investigate how molecular mechanisms involved in eusocial behaviors may have evolved from a solitary ancestor. I collected brain gene expression profiles from M. rotundata associated with nesting phase and mating status. Nesting phase affects the expression of hundreds of genes while mating status affects very few genes. Orthologs of many of the genes associated with M. rotundata nesting phase have previously been shown to be associated 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 in this dissertation leverages the power of new genomic technologies and uses a comparative approach to provide new insights into mechanisms of social evolution.

Graduation Semester

2013-12

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Copyright 2013 Brielle Fischman

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