Normally, species evolve characteristics over the course of several generations rather. However, in an attempt to save their species from extinction, the little brown bat has shown evidence of expediating the process.
Since the 2006 arrival of white-nose syndrome, the little brown bat population—once one of the most common bats in eastern North America—has been decimated; their population declining by more than 90 percent. White-nose syndrome (WNS), caused by the fungus Pseudogymnoascus destructans (Pd), infects hibernating bats causing them to wake with unusual frequency, thus burning up fat they need to survive the winter.
Scientists all over the world have been researching a cure for WNS, but to no avail thus far. Biologists from the University of Michigan, however, have finally delivered some good news—the first genetic evidence of resistance in some bats to WNS.
For their study, published in Scientific Reports, Giorgia Auteri and Lacey Knowles collected tissue samples from 25 little brown bats killed by WNS and nine bats that survived the disease. The deceased little brown bats were found during the winter in or near hibernation sites in the western Upper Peninsula of Michigan. Surviving bats were sampled in the summer after they emerged from hibernation—with visible wing lesions and scars from the fungus. WNS first presented in Michigan in 2014.
In the laboratory, Auteri and Knowles extracted DNA from the tissues, sequenced it, and then mapped the sequence to a previously generated reference genome for the little brown bat species. The researchers found significant differences in three genes associated with arousal from hibernation (GABARB1), breakdown of fats (cGMP-PK1) and echolocation (FOXP2), as well as a fourth gene (PLA2G7) that regulates the release of histamines from mast cells.
"Because we found differences in genes associated with regulating hibernation and breakdown of fats, it could be bats that are genetically predisposed to be a little bit fatter or to sleep more deeply are less susceptible to the disease," Auteri, first author of the paper, told Laboratory Equipment.
Specifically, the researchers pointed to FOXP2, the ecolocation gene, as a critical target. The function of the gene hints that summer activities, such as hunting via echolocation, may be an important determinant of which bats survive the winter.
“This suggests that conservation of summer foraging habitat—not just winter hibernation sites—may promote population recovery in bats affected by white-nose syndrome,” said Auteri.
Since little brown bats exclusively rely on insects for their food, Auteri said it's important for humans to keep to best practices for a pollinator-friendly habitat, such as planting native plants and avoiding pesticide use. Still, little brown bats face an uphill battle. They only birth one pup a year, so even if they are able to adapt and fend off the disease, recovery of the species will take some time. Wildlife conservation officials will play an important role in bats’ conservation.
While it’s too early to determine if the observed genetic differences were caused by evolutionary adaptation driven by natural selection, it’s a strong possibility—one the researchers will continue to explore in a larger follow-up study.
“The adaptation we document in this study was rapid, but is not unheard of,” said Auteri. “Evolutionary adaptation is about the genetic makeup of the population changing, not the individual. So, when a large proportion of the population dies off because of a potential natural selection event (like white-nose syndrome), it's not surprising that the remaining population is characterized by different genetics in some areas of the genome. The surviving population may previously have been a subset of the initial, pre-disease population, but now the genetics of the population, in general, seems to have changed due to natural selection, which imposed large die-offs.”
In a larger follow-up study, the researchers will look at more bat populations across other areas of the Midwestern United States. They will also be doing full-genome sequencing to gain a more specific understanding of which genes are influenced by the disease.
Photo: Little brown bats in a cave in New York. Credit: Al Hicks, New York Department of Environmental Conservation.