Quaternary climate instability is correlated with patterns of population genetic variability in Bombus huntii

Abstract

Climate oscillations have left a significant impact on the patterns of genetic diversityobserved in numerous taxa. In this study, we examine the effect of Quaternary climate instability on population genetic variability of a bumble bee pollinator species,Bombus huntii in western North America. Pleistocene and contemporary B. huntiihabitat suitability (HS) was estimated with an environmental niche model (ENM) byassociating 1,035 locality records with 10 bioclimatic variables. To estimate geneticvariability, we genotyped 380 individuals from 33 localities at 13 microsatellite loci.Bayesian inference was used to examine population structure with and without apriori specification of geographic locality. We compared isolation by distance (IBD)and isolation by resistance (IBR) models to examine population differentiation withinand among the Bayesian inferred genetic clusters. Furthermore, we tested for theeffect of environmental niche stability (ENS) on population genetic diversity withlinear regression. As predicted, high-latitude B. huntii habitats exhibit low ENS whencompared to low-latitude habitats. Two major genetic clusters of B. huntii inhabitwestern North America: (a) a north genetic cluster predominantly distributed northof 28°N and (b) a south genetic cluster distributed south of 28°N. In the south genetic cluser, both IBD and IBR models are significant. However, in the north geneticcluster, IBD is significant but not IBR. Furthermore, the IBR models suggest that lowlatitude montane populations are surrounded by habitat with low HS, possibly limiting dispersal, and ultimately gene flow between populations. Finally, we detectedhigh genetic diversity across populations in regions that have been climatically unstable since the last glacial maximum (LGM), and low genetic diversity across populations in regions that have been climatically stable since the LGM. Understanding howspecies have responded to climate change has the potential to inform managementand conservation decisions of both ecological and economic concerns.