Bumble Bee Species Distribution and Genetic Structure of Bombus vagans in the Southern Appalachians

Rayfield, Eric

ABSTRACT: Bumble bees (Bombus spp.) have faced significant declines worldwide in the past 60 years due to human driven climate change, disease, habitat loss, and intensive farming practices. Twelve species of bumble bee in North America are currently listed as vulnerable. More of the 46 North American species could face declines, but with little baseline data and routine monitoring of populations, their fate is uncertain. With decreased population numbers, bumble bees are susceptible to reduced fitness through loss of genetic diversity. If bumble bees maintain a high degree of dispersal among populations, they may be able to maintain sufficient genetic diversity and persist in a changing climate and survive anthropogenic stressors. This study evaluated the relative abundance and distribution of Bombus species along a 900 km MegaTransect crossing three National parks in the southern Appalachians: Shenandoah National Park, Blue Ridge Parkway, and Great Smoky Mountains National Park. Additionally, this project investigated the population genetics and dispersal preferences of Bombus vagans, a locally abundant bumble bee that is native to eastern US and high elevations in the southern Appalachians. I coordinated citizen science volunteers to collect bumble bee specimens from 390 roadside habitats within the national parks. I generated species distribution maps based on presence data using Maximum Entropy modeling software. I then used microsatellite markers to examine population genetic structure of Bombus vagans and used Maxent and Circuitscape geospatial modeling programs to elucidate the role that landscape features play in population genetic structure through isolation by distance and isolation by resistance. I identified ten Bombus species among the 3700 bumble bees sampled at three parks, but species diversity was heavily skewed by one dominant species, Bombus impatiens. Two species of concern, Bombus affinis and Bombus terricola, were not present in any of the sites sampled. Bombus vagans genetic analysis indicated some levels of inbreeding within a few populations but overall genetic diversity was stable. Models including both isolation by resistance and isolation by distance described more genetic variation among Bombus vagans populations than isolation by distance alone, suggesting that gene flow follows a nonlinear pattern. Interestingly, one population was highly genetically distant from all the rest, suggesting a potential cryptic species. The best fitting Circuitscape models indicated a habitat dispersal preference of high solar radiation, habitat openness, and imperviousness. Maps of modeled dispersal pathways seemed to follow rural roadways. These patterns indicate that Bombus vagans, and potentially other bumble bees, may be using roadways to maintain population connectivity. Conservation management strategies should be directed towards creating more roadside pollinator habitat by planting native gardens and decreasing mowing frequency.

Bumble Bee Species Distribution and Genetic Structure of Bombus vagans in the Southern Appalachians

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