Eastern Massasauga Rattle Snakes are Resorting to Incest and Humans May Be to Blame

Michigan’s rattlesnakes have been separated into small, isolated populations thanks to human roads, farms, and buildings. And that’s a serious problem, according to a new study in the Proceedings of the National Academy of Sciences, which shows that these already threatened snakes are being forced to mate with members of their own populations, sapping their ability to survive and reproduce.

“Even a single road can isolate populations,” said biologist Sarah Fitzpatrick, a study author and an associate professor at Michigan State University, according to a press release. “They’re very vulnerable to even minor disturbances to their habitat.”

Eastern Massasauga Rattlesnake

The Eastern Massasauga rattlesnake (Sistrurus catenatus) is the only venomous snake that’s seen in Michigan, and one of the only venomous snakes that slithers throughout the Midwestern United States.

While it may have a bad rap — bites are relatively rare but dangerous, sometimes deadly — this thick-bodied, grayish-brownish snake is still important to the health of the Midwest wetlands, consuming rodents such as mice and rats and preventing their populations from reaching human barns and homes.

According to the U.S. Fish and Wildlife Service, however, habitat loss and fragmentation have left this misunderstood species threatened wherever it is found, with humans limiting the mobility of Eastern Massasaugas across their traditional range.

That means that these snakes are more likely to reproduce with members of their same population — including their relatives — resulting in offspring that are less able to survive, and less able to produce surviving offspring themselves.

Rattlesnake Reproduction

To learn more about this phenomenon, researchers studied over 1,000 snakes in Michigan over the course of 15 years. They found that the most inbred individuals were 11.6 percent less likely to survive from year to year and 13.5 percent less likely to produce surviving offspring.

According to the study authors, the research shows that the restoration of rattlesnake habitat is needed, not only in Michigan, but in other Midwestern states, as well.

“These are fairly large and stable populations of Eastern Massasaugas,” Fitzpatrick said in the release. “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.”

Capturing and Recapturing Rattlesnakes

To arrive at their results, the Fish and Wildlife Service-funded researchers trudged through Michigan’s wetlands with rubber boots and snake tongs. Whenever they stumbled across an Eastern Massasauga, they scooped it up, measured it, and sampled its blood, which they then analyzed to sequence its genome. This allowed the team to recreate the ancestry of any one snake, and to compare the ancestry of any two individuals that were collected.

A researcher in a black shirt uses snake tongs to catch a gray rattlesnake with brown-black blotches in the tall grass. — Researcher team members used snake tongs to catch Eastern Massasauga rattlesnakes for their 15-year study.
(Image Credit: Sarah Fitzpatrick)

The team implanted tiny microchips called passive integrated transponders, or PITs, into each Eastern Massasauga to make identifying which snakes were recaptured after their release easier. Over the course of 15 years, the researchers revisited the wetlands, capturing and recapturing the same snakes to track their survival.

“This long-term field monitoring is the backbone of the study,” said biologist Meaghan Clark, another study author and a former Ph.D. student at Michigan State University, according to the release. “Having people out each season catching these snakes made all of this possible.”

The results revealed that conservation efforts are necessary to help Eastern Massasaugas survive and reproduce in Michigan and elsewhere. Among the possibilities for these conservation efforts are habitat restoration projects — including the construction of wildlife crossings — and snake relocation projects, which would promote habitat connectivity and prevent population declines due to inbreeding.

The result might be stronger and healthier wetlands across the Midwest, all thanks to these threatened and misunderstood snakes.

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