Abstract
Climate oscillations have left a significant impact on the patterns of genetic diversity observed 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. huntii habitat suitability (HS) was estimated with an environmental niche model (ENM) by associating 1,035 locality records with 10 bioclimatic variables. To estimate genetic variability, we genotyped 380 individuals from 33 localities at 13 microsatellite loci. Bayesian inference was used to examine population structure with and without a priori specification of geographic locality. We compared isolation by distance (IBD) and isolation by resistance (IBR) models to examine population differentiation within and among the Bayesian inferred genetic clusters. Furthermore, we tested for the effect of environmental niche stability (ENS) on population genetic diversity with linear regression. As predicted, high‐latitude B. huntii habitats exhibit low ENS when compared to low‐latitude habitats. Two major genetic clusters of B. huntii inhabit western North America: (a) a north genetic cluster predominantly distributed north of 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 genetic cluster, IBD is significant but not IBR. Furthermore, the IBR models suggest that low‐latitude montane populations are surrounded by habitat with low HS, possibly limiting dispersal, and ultimately gene flow between populations. Finally, we detected high 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 how species have responded to climate change has the potential to inform management and conservation decisions of both ecological and economic concerns.
Highlights
Geographic instability of ecosystems due to Quaternary climate change has left a lasting imprint on the compostion and diversity of populations and species across the planet (Hewitt, 1996, 2000)
Our population genetic study of B. huntii found that populations in regions that have been climatically unstable since the last glacial maximum (LGM) exhibit high genetic diversity, whereas regions that have been climatically stable since the LGM exhibit low genetic diversity (Figure 6b–c)
We found that high-latitude populations are associated with high within-population genetic diversity, and low-latitude populations are associated with reduced within-population genetic diversity (Figure 6b–c)
Summary
Geographic instability of ecosystems due to Quaternary climate change has left a lasting imprint on the compostion and diversity of populations and species across the planet (Hewitt, 1996, 2000). A decrease in the geographic spread of suitable habitat over time may lead to a population range contraction, cascading toward a population bottleneck, genetic drift, and a possible loss of genetic diversity (Pauls et al, 2013). The geographic expansion of suitable habitat over time may facilitate a population expansion, which may lead to a loss of genetic diversity due to founder effect, as the establishing population is typically made up of a small number of colonizing individuals (Pauls et al, 2013). Colonization into new suitable habitat may attract individuals from a diverse pool of populations and result in an increase in population genetic admixture (Ortego, Gugger, & Sork, 2015). Understanding how biodiversity responds to environmental change has the potential to inform effective management decisions for species of ecological and economic concern
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