HOW DOES GENETIC VARIATION INFLUENCE HONEY BEE (APIS MELLIFERA) DRONE FERTILITY TRAITS?

In honey bees, male fertility is directly involved in colony fitness. Males not only provide fifty percent of colony genetics, but they also provide material benefits involved with female fertility. Recent evidence suggests there is tremendous variation in drone fertility. Of drones which are sexually mature, as few as one in ten may be able to produce enough sperm to successfully inseminate a queen. If drones are not producing healthy sperm, their mates will not produce healthy colonies. Despite this, we have very little understanding of precisely how variation in drone reproductive quality is generated. Specifically, we know comparatively little about the role genetics plays in shaping drone reproductive traits. This standing genetic variation can contribute to phenotypic variation observed among honey bee stocks and contribute to the success (or failure) of colonies. The major goal of this thesis is to identify the major mechanisms and genes driving genotypic and phenotypic variation in honey bee males. First, we used a population genetics approach to estimate the evolutionary impact of haploid selection (Chapter 2) and variation in sexual selection (Chapter 3) on male genes. In Chapter 2, we found genes expressed by males had an increased genetic diversity, rate of adaptation, and more efficient purifying selection than non-haploid selected female-expression genes. This suggests haploid and sexually- expressed genes experience increases in the rate of molecular evolution. In Chapter 3, we found selection on sperm length shifted over evolutionary time within corbiculate bees, resulting in different strengths of sexual selection. As selection for sperm length intensified in male bees, there was rapid evolution of expression patterns and gene sequences associated with male-biased genes. Second, we used a quantitative genetics approach to connect genetic variation to the trait components of fitness (Chapter 4). We identified key genes connected to honey bee male sperm and maturity traits. These genes also appear to have different rates of evolution. Overall, we combined both population and quantitative genetic approaches to provide comprehensive insights into the evolution of honey bee male genotypes and phenotypes. This powerful approach allowed me to identify the genetic and mechanistic underpinnings driving variation in fitness-related traits. This information can be used to identify candidate genes associated with honey bee male fitness.