How haplodiploidy acts as an exaptation for extraordinary reproductive systems in the Hymenoptera

Abstract

In this thesis I investigate some instances of highly unusual reproductive biology in the honey bee. You might ask why I have investigated the weird rather than the mundane, which is surely more important to the biology of the species. To this I would answer that it is often the exceptions that yield greater biological insights than the normal, especially in social insects. The honey bee is a haplodiploid insect in which unfertilized eggs develop into males and fertilised eggs develop into females. Haplodiploidy has significant consequences for egg development since the act of being laid is sufficient to initiate embryogenesis regardless of fertilization. As my thesis will show, this leads to all number of opportunities for unusual development. For instance, just as the egg’s nucleus can start dividing without syngamy with a sperm cell, so too can a sperm nucleus that finds its way into the egg start to divide. providing endless opportunities for improbable kinds of development. I have uncovered bees with two fathers but no genetic mother, bees with two fathers and a mother, mosaic bees that have bits of different fathers, triploid workers, triploid queens, workers that can clone themselves and queens that can not. All this weirdness demonstrates that haplodiploidy is a remarkable exaptation for evolutionary novelty. Having uncovered new modes of development in the honey bee I turn my attention to the regulation of reproduction in the queen. While the regulation of worker fertility is quite well understood very little is known about queens. Queens stop laying in winter, in preparation for swarming, and when isolated from workers by beekeepers. I document the physiological and molecular changes that accompany these periods of temporary sterility in queens. In my final chapter I develop new ideas about how haplodiploidy provides opportunities for novel social structures in social insects. And I show how honey bees can be used to explore the space of possibilities.