Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Dr. Graham Thompson

Abstract

Eusocial breeding systems are characterized by a reproductive division of labour. For many social taxa, the queen signals her fecundity to her daughters via a pheromone, which renders them sterile. Solitary insects, in contrast, lack social organization and their personal reproduction is not regulated by social cues. Despite these radically different breeding habits between these two taxa, one prediction from sociogenomic theory is that eusocial taxa evolved their complex caste system through co-option of pathways already present in solitary ancestors. In this thesis, I present a series of comparative experiments that provide support for these conserved genes and gene pathways that regulate reproduction in social versus non-social taxa. First, I show that distinctly non-social Drosophila melanogaster can respond to a highly social Apis mellifera pheromone (QMP) in a manner similar to sterile worker bees – namely, by turning off their ovaries and foregoing reproduction. Second, I show that this conspicuous interspecific response is conserved at a genetic level, where the presence of certain foraging alleles can elicit variable responses to the pheromone in a manner similar to that in the bee. Third, I suggest that solitary and eusocial species use a conserved olfactory signaling mechanism to elicit reproductive responses to QMP. Using mutant Drosophila lines and an RNAi-mediated screen of olfactory receptors, I identify five top receptors as candidates for the perception of QMP and subsequent reduced ovary phenotypes. Lastly, I use Drosophila to investigate the functional association between two opposing social cues, royal jelly and QMP and their ability to modulate ovarian development. These results showcase the power of the comparative approach in identifying genes and gene pathways involved in the regulation of worker sterility, and suggest that the genetic basis of characteristically eusocial behaviours like reproductive altruism, are conserved in non-social insects.


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