Genetic follow-up of the offspring of felines that were brought to the island 30 years ago validates a population viability analysis
The return of 32 Bobcat cats to an island off the coast of Georgia more than three decades ago created the perfect experiment to examine the accuracy of a genetic modeling technique that predicts the extinction of isolated wildlife populations.
This is the conclusion reached by Pennsylvania researchers who continue to monitor bobcat populations on the National Seashore on Cumberland Island, and who conducted a study comparing and contrasting Cumberland Island cats with a group of Bobcats on Kiawah Island off the coast of South Carolina.
The research was led by Cassandra Miller Butterworth, Associate Professor of Biology at the Pennsylvania Beaver State, and Duane Diefenbach, Associate Professor of Wildlife Ecology of Pennsylvania, who, as a PhD candidate at the University of Georgia in 1989, reintroduced Bobcats captured in Georgia. Mainland to Cumberland Island. Before liberating the bobcats on the island, he drew blood samples from the animals and froze them. DNA in these samples now serves as a baseline for comparing how the population is performing.
The reintroduction of the bobcat was part of Diefenbach’s doctoral research, in which he documented the survival and reproduction of reintroduced bobcat cats and collected blood samples from the first kittens born on the island. Since then, he has returned to the island several times over the years with students and volunteers to collect bobcat scones from which DNA is extracted to monitor the genetic health of the population.
There are now 24 bobcats on the island of Cumberland, which are separated by open waters from the mainland and which prevent mainland bobcats from migrating. DNA taken from the scrap allows scientists to identify individual bobcat cats, which enables them to estimate abundance, survival rates and measure levels of inbreeding.
“Since we had DNA from the founding population, we were able to document the loss of genetic diversity over time in the population,” said Diefenbach, head of the Pennsylvania Cooperative Unit for Fish and Wildlife Research, which is based at the Pennsylvania State College of Agriculture. Sciences. “Over the past 30 years, the population has lost about 15% of its genetic diversity. There appears to be some incidence of inbreeding, but it is generally low.”
Over the past decade, Diefenbach has collaborated with Miller-Butterworth, a wildlife geneticist, to analyze the DNA of bobcat cats. Her lab handled all molecular analyzes from blood samples.
Diefenbach and Miller Butterworth also evaluated the number of bobcat on Kiawah Island. After fishermen in 2015 and 2016 donated tissue samples from Bobcats on mainland South Carolina, researchers determined that the Bobcats occasionally traveled in and out of that island, most likely over a vehicle bridge.
“In Kiawah, we studied genetics and found that approximately every five years, a bobcat from the mainland contributes to the formation of the genes of the islanders,” Miller Butterworth said. “Thus, the genetic diversity on Kiawah Island is lower than in South Carolina, but still higher than on Cumberland Island.”
The research results were recently published in Global Environment and Conservation, Indicates that the probability of the Cumberland Bobcat becoming extinct will continue to increase over time. By 2040, researchers have predicted that the risk of extinction will rise to about 20% without any human intervention to regain the loss in genetic diversity, perhaps by introducing a bobcat from the mainland every four or five years.
Nevertheless, the findings provide good news for people trying to protect endangered species, Miller Butterworth noted.
“We found that population viability models that predict the fate of the population do a good job at predicting long-term loss of genetic diversity and population size,” she said. “I was surprised how much the modeling and experimental data matched – you don’t see that often. When we were doing population viability analyzes, the predictions we got for genetic diversity, or heterozygosity, almost exactly matched what we were finding with our experimental DNA data.”
Miller Butterworth explained that the Cumberland Island bobcat study is valuable because it yielded information that could be useful in future research used to save endangered feline populations, such as the Iberian lynx or the Eurasian lynx, which may have a high risk of extinction. Bobcats are not threatened as a species, but an isolated population on Cumberland Island simulates an endangered species scenario in which populations become isolated due to loss of habitat and fragmentation and lose genetic diversity over time – an increasingly common scenario for many endangered species.
“The benefit is that we can use this as a case study, or test case, to find out what works to re-establish the viability of a population, and then that knowledge can be used to extrapolate what might work for endangered species,” she said. Sad, but it won’t cause you to lose a species. “
Also involved in the research is Pennsylvania Jesse Edson, director of the gene lab, and Tess Gingerie, research technologist, both in the Division of Ecosystem Science and Management. The other members of the team are Leslie Hansen, Los Alamos National Laboratory, Los Alamos, New Mexico; James Jordan, Kiawah Island, South Carolina; And Amy Russell, Department of Biology, Grand Valley State University, Allendale, Michigan.
Support for the project were provided by the National Park Service and the United States Geological Survey, Kiawah Island City, and Penn State Beaver.