Myotis bats roosting together. Credit: Nicole Foley/Texas A&M University School of Veterinary Medicine and Biomedical Sciences
If/when there is another global pandemic, many scientists believe a zoonotic disease will be at the center of the outbreak. It’s a more than reasonable hypothesis, especially given bats’ suspected role in the COVID-19 pandemic. Focusing, specifically, on bats also has credibility as many species of bats are immune to deadly human diseases, such as coronaviruses, Ebola and even cancer.
Studies, especially those published in the last four years, have pointed to various mechanisms that enable bats’ incredible immune systems, including a specific enzyme, stem cells, traditional evolution, and even rapid evolution.
Now, researchers at Texas A&M have added another possible protective mechanism to the list—mating swarms.
“Understanding how bats have evolved viral tolerance may help us learn how humans can better fight emerging diseases,” said study author Nicole Foley from the Texas A&M School of Veterinary Medicine & Biomedical Sciences (VMBS).
To find this answer, Foley and her team focused on Myotis bats, which are found almost all over the world and host a large diversity of viruses. The first step was to map the evolutionary tree of these bats—a task that comes with some complications. Not only are Myotis bats the second-largest genus of mammals with over 140 species, they all look very similar to each other. To make matters worse, Myotis bats (as well as other species) also participate in swarming behavior during mating.
“You can think of swarming behavior like a social gathering; there’s lots of flight activity, increased communication and inter-species mingling,” said Foley. “For bats, it’s not unlike going to a [human] nightclub.”
Swarming creates increased numbers of hybrids—individual bats with parents from different species.
“It can be very hard to distinguish [Myotis bats] from each other, and then hybridization makes it even more difficult,” said Foley. “If we’re trying to map out how these bats evolved so we can understand their disease immunity, being able to tell who’s who is very important.”
In the new study, published in Cell Genomics, Foley and colleagues collaborated with researchers from Ireland, France and Switzerland to sequence the genomes of 60 Myotis bat species. This work allowed them to untangle the genetic code for hybridization so they could tell more clearly which parts of the DNA represented the species’ true evolutionary history and which parts arose from hybridization.
With that part of the puzzle solved, the researchers were finally able to examine the genetic code more closely to see how it might shed light on disease immunity. They found that immune genes were some of those most frequently exchanged between species while swarming.
“Swarming behavior has always been a bit of a mystery for researchers,” Foley said. “Now we have a better understanding of why this particular behavior evolved—perhaps to promote hybridization, which helps spread beneficial immune gene variants more widely throughout the population.”
While the study sheds some light on virus transmission, the unexpected role hybridization played in the results opens the door to new questions about its role and importance in evolution.
“These results have led us to wonder to what extent hybridization has obscured genomicists’ knowledge of mammalian evolutionary history so far,” Foley said. “Now, we’re hoping to identify other instances where hybridization has occurred among mammals and see what we can learn about how they are related and even how and why genomes are organized the way that they are.”