Diploid male frequencies of Bombus flavifrons across a gradient of habitat development in Anchorage, Alaska

Bumble bees, like most hymenopterans, have a haploidiploid sex determination system, in which males develop from unfertilized eggs (haploid) and females from fertilized ones (diploid). However, inbreeding and other extrinsic factors, such as habitat loss and fragmentation, can increase the production of inviable or effectively sterile diploid males, which inherit two identical alleles (homozygosity) at the sex determination locus. Diploid males can still mate, and high diploid male production (DMP) may trigger a feedback loop that negatively impacts population size and fitness, leading to further loss of genetic diversity. This research examines the prevalence of diploid male frequencies in wild populations. In addition, we examine the relationship between DMP, habitat development, and vegetation, providing insight into the impact of human-modified landscapes on bumble bee population health.

In the Summer of 2024, we collected 545 male Bombus flavifrons from 21 sites, encompassing various levels of urban development, across Anchorage, Alaska (n = 7 - 43 males/site). To estimate diploidy (the proportion of males/site, we extracted DNA from the midleg of each specimen and genotyped using 11 microsatellite loci, previously described in the literature. This study integrates fine-scale geographic sampling with molecular tools to assess genetic diversity and the occurrence of diploid males in wild populations. Additionally, it compares male morphological traits (e.g., body size, tarsal length) across a gradient of habitat development to explore potential correlations among male morphology, diploid status, and whether these characteristics can serve as indicators of population health and fitness.