Abstract
The little brown bat (Myotis lucifugus) is one of the most widespread bat species in North America and is experiencing severe population declines because of an emerging fungal disease, white-nose syndrome (WNS). To manage and conserve this species effectively it is important to understand patterns of gene flow and population connectivity to identify possible barriers to disease transmission. However, little is known about the population genetic structure of little brown bats, and to date, no studies have investigated population structure across their entire range. We examined mitochondrial DNA and nuclear microsatellites in 637 little brown bats (including all currently recognized subspecific lineages) from 29 locations across North America, to assess levels of genetic variation and population differentiation across the range of the species, including areas affected by WNS and those currently unaffected. We identified considerable spatial variation in patterns of female dispersal and significant genetic variation between populations in eastern versus western portions of the range. Overall levels of nuclear genetic differentiation were low, and there is no evidence for any major barriers to gene flow across their range. However, patterns of mtDNA differentiation are highly variable, with high ΦST values between most sample pairs (including between all western samples, between western and eastern samples, and between some eastern samples), while low mitochondrial differentiation was observed within two groups of samples found in central and eastern regions of North America. Furthermore, the Alaskan population was highly differentiated from all others, and western populations were characterized by isolation by distance while eastern populations were not. These data raise the possibility that the current patterns of spread of WNS observed in eastern North America may not apply to the entire range and that there may be broad-scale spatial variation in the risk of WNS transmission and occurrence if the disease continues to spread west.
Highlights
Understanding how host movement patterns influence the transmission of pathogens is critical to the development of effective prevention and control strategies, and to the conservation and management of host populations during and after disease outbreaks
Assuming that rates of contact among individuals leading to gene flow are indicative of contacts that could result in disease transmission, genetic methods provide a useful alternative to traditional demographic approaches as a means of examining host movements and their impact on disease transmission [1]
Whether the observed variation is representative of discrete genetic clusters rather than isolation by distance is debatable, but overall, it is clear that levels of nuclear genetic differentiation are low, and there is no evidence for any major barriers to nuclear gene flow across the range of little brown bats
Summary
Understanding how host movement patterns influence the transmission of pathogens is critical to the development of effective prevention and control strategies, and to the conservation and management of host populations during and after disease outbreaks. Evidence from empirical studies employing population and landscape genetic approaches has demonstrated that landscape features, such as mountains and rivers that limit host gene flow, often represent barriers to disease transmission [1,2,3,4,5,6], alternative mechanisms of pathogen dispersal, including humans and other highly mobile intermediate hosts, may override the influence of primary host population genetic structure [1]. Mortality of bats likely occurs through the loss of physiological homeostasis [11], possibly associated with dehydration and electrolyte depletion [12,13], leading to more frequent arousal behavior and premature loss of fat reserves [14,15] Since it was first discovered in New York State during the winter of 2006–07, WNS has since spread to 27 additional states and five Canadian provinces, and is known to affect at least seven species of hibernating bats [16]. The rapid emergence, and the geographic and taxonomic spread of the disease have raised serious concerns about the long-term survival of hibernating bat species in eastern North America, and have highlighted our lack of knowledge of the factors that may influence WNS transmission and spread to currently unaffected regions
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