Some populations of the little brown bat (Myotis lucifugus) appear to be stabilizing in the years following catastrophic declines due to white-nose syndrome (WNS). Recent modeling suggests that this may be due to a selective sweep of the pathogen through bat populations in favor of more robust genotypes. If remnant infected colonies contain genetically resistant individuals that continue to survive and reproduce, population dynamics could revert to positive growth, a phenomenon known as evolutionary rescue. To better understand the evolutionary potential of infected bat populations, we collected DNA samples from little brown bats from three locations: New Jersey, New York, and Vermont, USA. For each site, we collected samples from 30 random individuals representing the genetic variation within the population before (2007-2008) and after (2016) population declines due to the disease. We then used low-coverage whole genome sequencing to characterize the genetic makeup of populations before and after WNS-caused population declines.
Results/Conclusions
In order to determine if remnant populations have undergone a selective sweep, we used the program ANGSD to call SNPs and estimate the site frequency spectrum for each population (before and after WNS). We found that remnant populations had reduced genetic diversity compared to their pre-WNS counterparts, suggesting either selection or a bottleneck. We then used a sliding window FST analysis to identify regions of the genome that are likely under selection. We found three regions that consistently contained multiple FST outliers, strong evidence that the reduced diversity is due to selection as opposed to a bottleneck. Two of these regions were unannotated (one in the mitochondrial DNA). The third region codes for a gene involved in neural development, suggesting that genetically-determined behavioral changes may be conferring a fitness advantage to the surviving bats. Further work is needed to determine how this robust genotype allows bats to survive WNS infection. This work will help inform management strategies for both remnant populations and populations that have not yet been exposed to WNS.