The brown tree snake has become one of the world's best-known examples of an invasive species - and a persistent headache for Guam's utility companies, who have to deal with hundreds of snake-related power outages each year.

Native to Australia and the South Pacific, the snake likely reached Guam sometime after World War II, possibly by hiding aboard military cargo planes. Its arrival had devastating consequences: brown tree snakes have driven many of Guam's native forest birds to local extinction, and in some parts of the U.S. territory, their numbers have climbed as high as 30,000 snakes per square mile.

The invasion has long puzzled biologists because Guam's population is believed to have begun with only a small number of snakes. Such a limited founding population usually creates a severe genetic bottleneck, reducing a species' ability to adapt. But a new University at Buffalo-led study, published on July 24 in Science Advances, suggests that brown tree snakes possess far more genetic variation than scientists previously recognized.

Researchers from UB and the U.S. Geological Survey (USGS) used advanced long-read sequencing to examine large sections of the snake's genome. They uncovered thousands of structural variants, including DNA segments that had been duplicated, deleted, or rearranged. Many of these variations were concentrated in genes related to immunity and smell.

"The brown tree snake is maybe not wildly diverse, but it has important sources of genetic diversity that have been underappreciated," says study corresponding author Trevor Krabbenhoft, PhD, associate professor in the UB Department of Biological Sciences.

This hidden genetic diversity may help explain how a population founded by only a handful of snakes survived intense inbreeding, adapted to Guam, and expanded so dramatically. The discovery may be discouraging for agencies that have spent decades trying to contain Guam's brown tree snake population - greater genetic flexibility could make the invasive species more resilient than previously assumed.

At the same time, the results may offer hope for endangered species with small or highly inbred populations. "It's possible that endangered species may have more flexibility in their genes than we realize," says first author Christopher Osborne, PhD, a former PhD student in Krabbenhoft's lab and now an aquatic biologist with SUNY Oswego.

When the team analyzed samples obtained from the USGS Brown Tree Snake Rapid Response Team, they identified more than 19,000 structural variants in the brown tree snake genome. These variations were not scattered randomly - they appeared especially often in genes involved in immune function and olfaction, or the sense of smell. Brown tree snakes depend heavily on smell to navigate and hunt, and the unusual diversity in their olfactory genes could also help explain a behavioral mystery: brown tree snakes are known to eat other snakes in their native range, but there is little evidence that they frequently prey on one another in Guam.

"The snakes' heightened sense of smell may allow them to recognize one another as something more like siblings - especially given the high levels of inbreeding - than as prey," says Levi Gray, PhD, a postdoctoral researcher in Krabbenhoft's lab.

Scientists still do not know whether the structural variants were already present before the snakes reached Guam or whether some appeared after the invasion began. Determining when these changes appeared will require comparisons with brown tree snakes from their native range. As Gray puts it, "Is it possible some of this diversity emerged after the invasion? It is, but we would have to sequence snakes from the native populations to know for sure."