Genetic connectivity among swarming sites in the wide ranging and recently declining little brown bat (Myotis lucifugus)

Abstract

Characterizing movement dynamics and spatial aspects of gene flow within a species permits inference on population structuring. As patterns of structuring are products of historical and current demographics and gene flow, assessment of structure through time can yield an understanding of evolutionary dynamics acting on populations that are necessary to inform management. Recent dramatic population declines in hibernating bats in eastern North America from white-nose syndrome have prompted the need for information on movement dynamics for multiple bat species. We characterized population genetic structure of the little brown bat, Myotis lucifugus, at swarming sites in southeastern Canada using 9 nuclear microsatellites and a 292-bp region of the mitochondrial genome. Analyses of F ST, ΦST, and Bayesian clustering (STRUCTURE) found weak levels of genetic structure among swarming sites for the nuclear and mitochondrial genome (Global F ST = 0.001, P < 0.05, Global ΦST = 0.045, P < 0.01, STRUCTURE K = 1) suggesting high contemporary gene flow. Hierarchical AMOVA also suggests little structuring at a regional (provincial) level. Metrics of nuclear genetic structure were not found to differ between males and females suggesting weak asymmetries in gene flow between the sexes. However, a greater degree of mitochondrial structuring does support male-biased dispersal long term. Demographic analyses were consistent with past population growth and suggest a population expansion occurred from approximately 1250 to 12,500 BP, following Pleistocene deglaciation in the region. Our study suggests high gene flow and thus a high degree of connectivity among bats that visit swarming sites whereby mainland areas of the region may be best considered as one large gene pool for management and conservation.

Keywords: Chiroptera; Myotis; dispersal; genetic structure; mating; swarming.

Figure 1

A male little brown bat (Myotis lucifugus) captured at swarming site in Nova Scotia, Canada. Photograph by Lynne Burns.

Figure 2

Sampling locations for Myotis lucifugus captured at swarming sites in southeastern Canada to assess population genetic structure. Geographic coordinates and names are not used due to the sensitive nature of swarming and hibernation sites; numbers correspond to site numbers in tables.

Figure 3

A median-joining network for Myotis lucifugus based on a 292-base-pair mitochondrial DNA segment of the control region coded by province. Circle size corresponds to haplotype frequency with inferred hypothetical haplotypes (mv) not sampled in the current study shown.

Figure 4

Mismatch distribution of Myotis lucifugus based on a 292-base-pair segment of the mitochondrial control region showing the observed frequency of pairwise differences among sequences (hatched line). The expected distribution (solid line) is for a population of constant size.

Figure 5

Bayesian skyline plot of the changes in effective population size backwards in time for Myotis lucifugus sampled from swarming sites in southeastern Canada. The x-axis represents time measured in years and the y-axis the population size (logarithmic) expressed as the product of the effective population size and the generation time in years (N_eτ).