While they may look alike, foxes on six different islands in California’s Channel Islands are actually very genetically different.
The reason for these differences? According to a recent study, it’s genetic drift — or the random fluctuation in the frequency of alleles or different versions of a gene — in an isolated population. “Because there’s such strong genetic drift, some subspecies have low genetic variation,” said associate professor at Colorado State University and lead author Chris Funk. This low genetic variation can cause some issues for the foxes such as inbreeding depression or the reduction in survival, reproductive rates and fitness.
In the study published in the journal Molecular Ecology, the researchers looked at the island foxes (Urocyon littoralis) on all six of the eight Channel Islands where they occur and found that the population with the lowest genetic variation was on San Nicolas Island, one of the smaller islands further from the coast. They also determined that each island fox population is genetically distinct and should be designated as a subspecies.
Using blood samples of the foxes taken by field biologists, the researchers estimated the effective population size of each island, which can be thought of as the number of individuals in a population that contribute offspring to the next generation. Effective population size is an important genetic parameter, as it determines the rate at which genetic variation is lost due to genetic drift, Funk says. They also found evidence for genetic bottlenecks on each of the islands, which is a reduction in population that leads to lower genetic diversity.
In addition, low genetic variation makes it difficult for species to evolve and adapt to environmental changes such as warmer weather or drought, Funk says. Also, when diseases are introduced, it’s more difficult for species to adapt and develop a resistance to novel diseases. “Low genetic variation raises a red flag and is something we’re looking at and concerned about for the persistence of foxes,” he said.
The San Nicolas population has declined over the last several years and while low genetic variation may have contributed to this, Funk says that environmental changes could also contribute to declines. “It could just be a really bad drought,” he said, adding that it might also be due to a decline in food sources for the omnivorous species since native vegetation and other species the foxes eat may have decreased in abundance during the drought. Further, there could be interactions between the environment and genetic variation that may be occurring. “Previous research suggests that inbreeding depression is less likely to occur when times are good and food and the environment are benign,” he said. “If conditions are bad, hot and dry then inbreeding depression may kick in, reducing survival and reproductive rates further.”
Funk recommends collecting more data on the subspecies to see if inbreeding depression is a problem for the foxes. The islands are currently managed by the Navy and it is up to them to decide how to manage the foxes. “I’m happy to work with people out there to design research programs to help answer really important questions and inform management decisions,” he said.
A Conservation Success Story
In the late 1990s, four of the six populations of Channel Island foxes were declining rapidly and were listed as endangered under the U.S. Endangered Species Act. Land managers including Park Service, the Navy, The Nature Conservancy and the Catalina Island Conservancy created an island fox recovery team and successfully worked together to recover the foxes. Because of the success of these efforts, the USFWS has proposed to delist the subspecies on San Miguel, Santa Rosa and Santa Cruz Islands and downgrade the subspecies on Santa Catalina Island from endangered to threatened. This success story was ultimately the result of a coordinated effort toward a common goal by the agencies involved, according to Funk.
“Even though the San Nicolas species is declining, I’m confident that as long as agencies work together to identify the problem, they can solve this,” Funk said. “We have the tools to figure out what’s going on and manage it appropriately.”
|Dana Kobilinsky is associate editor at The Wildlife Society. Contact her at firstname.lastname@example.org with any questions or comments about her article. You can follow her on Twitter at @DanaKobi.|