Inbreeding among Michigan’s rare rattlesnakes is harming their ability to survive

EAST LANSING, MI – Michigan is home to a single species of venomous snake, and the isolated pockets of its populations are making it more likely it will go extinct.

Researchers at Michigan State University found the fragmented nature of the wetlands habitats where eastern massasauga rattlesnakes are still found leads to inbreeding among their secluded populations. As a result, the reproductive rates of the snakes are on the decline, a 15-year study showed.

Biology experts argue that reconnecting habitat corridors for the federally threatened reptile may be the best way to reverse this negative trend affecting one of Michigan’s rarest keystone species.

Michigan is considered to have the most robust U.S. population of the eastern massasauga rattlesnake species. That is why this discovery in Michigan could have striking implications for the wider remaining Midwestern population.

“The fact that we’re detecting problems from inbreeding in these populations is concerning, given that many other populations throughout the Midwest are much smaller and even more fragmented,” said MSU Associate Professor Sarah Fitzpatrick.

The MSU researchers studied isolated populations of the snakes in Michigan’s Barry and Cass counties dating back to 2009. Genetic pedigrees were traced for more than 1,000 of the pit vipers collected as part of the long-term study.

Scientists learned that roads, buildings, and even farms were blocking habitat corridors the rattlesnakes would otherwise use during breeding season. This led to increased instances of snakes mating with their genetic cousins.

“They’re very vulnerable to even minor disturbances to their habitat,” Fitzpatrick said in a statement. “Even a single road can isolate populations.”

According to the new study published in the Proceedings of the National Academy of Sciences, researchers learned the most inbred snakes were 13% less likely to have their offspring survive and had a nearly 12% lower annual survival rate.

The scientific term for the problem is called “inbreeding depression.”

Possible solutions could include restoring habitat, building road underpasses, or even moving imperiled rattlesnakes to new habitats, all ways to bolster the gene pool for the species.

The MSU researchers tracked the individual snakes in the study areas over the years by inserting a type of microchip tag into each captured snake. That is similar to another years-long scientific study into eastern massasauga rattlesnakes at the Camp Grayling military base near Grayling.

Eastern massasauga rattlesnakes were added to the federal list of endangered species in 2016 because of significant population drops attributed to habitat loss and fragmentation.

The snakes eat small rodents like mice and voles but will sometimes also eat reptiles like frogs and other snakes. The species thrives in wetlands and uses nearby uplands to breed and hibernate during winter months.

Related: Rattlesnake wranglers help conserve Michigan’s only venomous snake at military base

And as a keystone species, the eastern massasauga is an indicator of high-quality wetland ecosystems. A decline in the venomous snakes means there’s something wrong with the habitat.

Although the temperaments of individual snakes vary, the eastern massasauga rattlesnake is generally considered among the most timid pit vipers. They typically won’t strike or bite unless stepped on or otherwise touched, which only rarely happens.

In addition to this research into the snakes genetically inbreeding, scientists are also studying the impact of climate change and wintertime snow depth loss on reproduction rates and overall survivability of the rattlesnake species.

Michigan and Ontario are considered the strongholds of the species, though limited pockets of the snakes can also still be found in New York, western Pennsylvania, Ohio, northern Indiana, Illinois, eastern Iowa, and Wisconsin.