Contemporary human‐altered landscapes and oceanic barriers reduce bumble bee gene flow

Abstract

Much of the world's terrestrial landscapes are being altered by humans in the form of agriculture, urbanization and pastoral systems, with major implications for biodiversity. Bumble bees are one of the most effective pollinators in both natural and cultivated landscapes, but are often the first to be extirpated in human-altered habitats. Yet, little is known about the role of natural and human-altered habitats in promoting or limiting bumble bee gene flow. In this study, I closely examine the genetic structure of the yellow-faced bumble bee, Bombus vosnesenskii, across the southwestern US coast and find strong evidence that natural oceanic barriers, as well as contemporary human-altered habitats, limit bee gene flow. Heterozygosity and allelic richness were lower in island populations, while private allelic richness was higher in island populations compared to mainland populations. Genetic differentiation, measured for three indices across the 1000 km study region, was significantly greater than the null expectation (F(ST) = 0.041, F'(ST) = 0.044 and D(est) = 0.155) and correlated with geographic distance. Furthermore, genetic differentiation patterns were most strongly correlated with contemporary (2011) not past (2006, 2001) resistance maps calibrated for high dispersal limitation over oceans, impervious habitat and croplands. Despite the incorporation of dramatic elevation gradients, the analyses reveal that oceans and contemporary human land use, not mountains, are the primary dispersal barriers for B. vosnesenskii gene flow. These findings reinforce the importance of maintaining corridors of suitable habitat across the distribution range of native pollinators to promote their persistence and safeguard their ability to provide essential pollination services.

Distance, elevation and environment as drivers of diversity and divergence in bumble bees across latitude and altitude

“…As a result, they experience a somewhat narrower and less variable bioclimatic niche, especially for temperature (Figure ), which we hypothesize may lead to more restricted gene flow (Lozier et al., ). Gene flow within B. vosnesenskii is also sensitive to land use and cover characteristics (Jha, ; Jha & Kremen, ), despite high range‐wide population connectivity (Lozier et al., ).…”

“…Previous studies have illuminated the role of abiotic factors on genetic diversity of bumble bees in the western United States (Jha, ; Koch et al., ; Lozier et al., ), however, have several limitations. For example, Lozier et al.…”

Estimates of accessible food resources for pollinators in urban landscapes should take landscape friction into account

“…Landscape friction has been used rather extensively in landscape ecology (mainly for mammals, birds, and amphibians), but potential effects on insect movements are still underrepresented (Zeller et al 2012), but see, for example, Jha and Kremen (2013) and Jha (2015). Our results suggest that accounting for landscape friction when quantifying available habitat in the surrounding landscape is important for insects (here bees and wasps), at least in urban landscapes.…”

Conservation genetics of bees: advances in the application of molecular tools to guide bee pollinator conservation

“…Bees are flying insects and can often forage long distances, but it is unclear which habitat features influence their patterns of dispersal. Population genetic studies can shed light on potential drivers of dispersal from inferred genetic structure (Jha 2015). At contemporary time scales, reduced genetic diversity in a population can increase the risk of inbreeding (Zayed and Packer 2005), and inbreeding depression can result in fitness declines, such as slower growth rates and lower reproductive rates (Whitehorn et al 2009).…”