This is the story of how an extremely inbred snake population conquered the island of Guam.
According to a new study published in Science Advances by researchers from the University at Buffalo and the U.S. Geological Survey, a species of snake that likely snuck its way onto the island somehow became so widespread that it started literally eating away at the population numbers of local birds, and all while defying the laws of biology.
The brown tree snake hitched a ride to Guam sometime after World War II, probably aboard military cargo. What likely began as a tiny handful of snakes quickly snowballed into an ecological disaster, as the numbers of the island’s native birds, bats, and lizards soon started dwindling. It wasn’t just the local animals, but the local human population that had to endure the wrath of the snakes, as they’d coiled themselves around electrical poles, causing regular power outages. In some areas, there were an estimated 30,000 snakes per square mile.
And all from a species that shouldn’t have survived, given how deeply inbred the snake population was, and how little genetic diversity all that inbreeding left them with to adapt to their new environment.
How the Snakes Have Survived Such Intense Inbreeding
But when researchers took a closer look at this snake population’s DNA, they found a bit more genetic diversity than they expected. The team used newer long-read DNA sequencing technology and discovered more than 19,000 previously hidden structural changes in the snakes’ genomes, large chunks of DNA that older techniques couldn’t easily detect. A lot of those genetic differences affect immunity, stress response, and smell, which is pretty important for a predator.
This enhanced sense of smell likely helped the snakes hunt all that Guam had to offer, while simultaneously letting snakes recognize fellow snakes as members of their family and not, say, lunch.
There is a chance that the genetic changes were already in the snakes by the time they reached Guam, but the researchers can’t say that definitively, as there is still a chance they developed afterward, at some point, in the incalculable number of generations that have spawned since they first arrived in World War II.
This story demonstrates a remarkable will to adapt and evolve, which is great for the snakes and bad for the biodiversity of Guam and for anyone whose job it is to stop an invasive species that’s seemingly eating nearly every living thing on the island and putting the small island’s electricity and a chokehold.
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