DNA in lip-rimmed bat droppings reveals unexpected eating habits

Poop is full of secrets. For scientists, digging in the droppings provides insight into animal nutrition and is particularly useful for understanding nocturnal or rare species. When animals eat, prey DNA travels all the way through animal digestive tracts and comes out again. Poop contains very precise information about the types of prey consumed. At the Smithsonian Tropical Research Institute (STRI), a team studied the eating habits of the lip-rimmed bat (Trachops cirrhosus) by examining their poop.

Bats hunt at night. This makes it difficult to observe their foraging behavior in nature. Analysis of traces of DNA in bat guano offers a more specific way to study how bats feed in the wild and to study how bats’ behavior changes depending on their eating habits.

“Because bats forage at night and in thick forest, you can’t watch what they eat with a day bird or mammal as you can,” said Patricia Jones, former STRI fellow, assistant professor of biology at Bowdoin College and lead author of the study . “So it feels so significant to take a look at the diet of the species that we thought we knew so much about, that they eat prey that we had no idea were part of their diet.”

The fringed bat, also known as the frog-eating bat, is well-suited for hunting frogs. The bats’ hearing is adapted to their low-frequency mating calls, and their salivary glands can neutralize the toxins in the skin of poisonous prey. Fringed bats also feed on insects, small reptiles, or birds and other bats. Researchers knew that these bats often find their prey by listening to mating calls, but it was not known whether they could find silent prey.

As expected, most of the DNA obtained from the fecal samples in the study belonged to frog species and many lizards, but the researchers also found evidence that the bats were eating other bats and even a hummingbird. In additional experiments, wild-caught bats with rim lips exposed to recordings of prey sounds and stationary prey models were able to detect silent, motionless prey as well as prey that were making noise. This led the researchers to conclude that the fringed bat is better able to locate prey through echolocation than previously thought.

“That’s interesting because we didn’t know that these silent bats could still spot prey,” said May Dixon, STRI fellow, graduate student at the University of Texas at Austin and co-author of the study. “Finding silent, still prey in the crowded jungle is seen as a really difficult task for echolocation. This is because when the bats echo in the jungle, the echoes from all the leaves and twigs bounce back along with the echoes from their prey, “masking” the prey. ”

These results could provide a new line of research into the sensory abilities and nutritional ecology of T. cirrhosus. It also contributes to a growing body of work suggesting that bats may be important nocturnal predators in the tropics for sleeping animals such as birds. The team also found unexpected frog species among their common prey.

“We found that T. cirrhosus often ate frogs of the genus Pristimantis,” said Jones. “I think this will open new avenues for research with T. cirrhosus as Pristimantis calls from the canopy and their calls are difficult to locate. So when T. cirrhosus consumes them, it means that they are looking differently than we understood before. ”

In the future, this novel combination of dietary DNA analysis and behavioral experiments can be used by other ecologists interested in the foraging behavior of a wide variety of animal species.

“It’s really exciting to see the doors that open when animal behavior is combined with metabar coding,” said Rachel Page, STRI employee. “Although we’ve studied Trachops intensively for decades, we actually know very little about its behavior in the wild. It was completely surprising to see prey appear in the diet that we had never expected, such as species of frogs whose mating calls did not seem to have acoustic parameters that were helpful for localization, and surprisingly prey that the bats apparently obtained through echo localization alone must have discovered like hummingbirds. This work makes us rethink the sensory mechanisms underlying the foraging behavior of this bat and opens all sorts of new doors to future questions. ”

Reference: “Sensory ecology of the frog-eating bat, Trachops cirrhosus, from DNA Metabar Coding and Behavior “by Patricia L. Jones, Timothy J. Divoll, M. May Dixon, Dineilys Aparicio, Gregg Cohen, Ulrich G. Müller, Michael J. Ryan and Rachel A. Page, October 21, 2020 , Behavioral ecology.
DOI: 10.1093 / beheco / araa100

Research team members are affiliated with STRI, Bowdoin College, SWCA Environmental Consultants, and the University of Texas at Austin. The research was funded by Smithsonian, the National Science Foundation DDIG # 1210655, and a PEO Scholar Award.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The institute promotes understanding of tropical biodiversity and its importance for human well-being, trains students to explore the tropics, and promotes conservation by raising public awareness of the beauty and importance of tropical ecosystems.