Bee conservation genetics

Bee populations (Hymenoptera: Apiformes) are experiencing a seemingly world-wide decline expected to have serious ecological and economic consequences. Ongoing efforts to examine the conservation biology of pollinators have largely ignored genetic aspects, either as a proximate cause of declines, or as a tool to aid in conservation programs. The explicit or implicit exclusion of genetics in bee conservation biology occurred mainly due to misconceptions regarding the immunity of haplodiploids to genetic perils in small populations, or to difficulties in extrapolating knowledge from conservation genetics studies of diploid animals to the haplodiploid bees. The primary purpose of my thesis is to examine the conservation genetics of bees, through theoretical, modeling, and empirical studies. I mainly concentrate on elucidating the consequences of an important but largely neglected aspect of bee biology: complementary sex determination. In addition, I explore the consequences of diet specialization on the population genetics of specialists using empirical studies.;The second component of my thesis addresses the influence of diet specialization on the population and conservation biology of bees. In chapter 5, I report on the isolation and characterization of 19 hyper-variable microsatellite markers, isolated from the pollen-generalist Lasioglossum leucozonium and the pollen-specialist L. oenotherae (Hymenoptera: Halictidae). Chapter 6 describes a population genetic study of the specialist L. oenotherae across its range in North America. Strong levels of genetic differentiation were detected between L. oenotherae populations, consistent with the hypothesis that specialization promotes isolation. I also detected signatures of inbreeding and drift in the southernmost L. oenotherae populations, which combined with anecdotal evidence of higher extirpation rates in that area, suggests that this bee is experiencing high threats to its viability either due to global change or more locally acting conditions in its southern range. Chapter 7 presents an empirical study of the population genetics of L. leucozonium in North America. This study was originally undertaken to compare and contrast the population genetics of the generalist L. leucozonium and the specialist L. oenotherae. However, genetic data from North American populations of L. leucozonium strongly suggest that this bee is actually not native to North America, as currently accepted. I present evidence supporting L. leucozonium's status as an exotic bee in North America, and attempt to reconstruct its invasion history based on genetic data. This chapter represents the first population genetic study of a solitary exotic bee, providing an interesting opportunity to examine how genetics and behavior interact to shape the success of exotic Hymenoptera (ants, wasps, and bees).;In addition to the above chapters, I also provide an introduction to the major themes of my dissertation (Chapter 1), and a concluding section summarizing the basic findings of my thesis, its contribution to the field of bee conservation genetics, and outlining future research plans (Chapter 8).;Complementary sex determination in haplodiploids leads to the production of inviable or effectively sterile diploid males from fertilized eggs homozygous at the sex locus. In chapter 2, I show using stochastic modeling that diploid male production greatly increases extinction risk in bee populations under a wide range of conditions. Further, this increased extinction risk in haplodiploids with complementary sex determination is an order of magnitude higher than the effects of inbreeding depression in diploid populations. Therefore, haplodiploids are more, rather then less, prone to extinction for intrinsic genetic reasons when compared to diploids. In Chapter 3, I show using a theoretical study that complementary sex determination can greatly reduce effective breeding population sizes in small populations. This occurs since diploid male production acts to reduce the number of breeding females and biases the secondary sex ratio in favor of haploid males. For chapter 4, I conducted an empirical population genetic study of an apparently common Panamanian orchid bee, Euglossa imperialis (Hymenoptera: Euglossini), where I found high levels of diploid male production and low effective population sizes. Given that census data are sometimes misleading, and often lacks sufficient power to detect declines, I proposed the use of diploid male frequency data to indicate pollinator decline.