Biologists have long wondered how such a small number of individuals from the invasive species managed to colonize the island so successfully.
Few invasive animals have reshaped an ecosystem as dramatically as the brown tree snake, a species commonly used in textbooks to illustrate the damage biological invasions can cause.
Native to Australia and the South Pacific, the snake reached Guam sometime after World War II, possibly as a stowaway on cargo aircraft. It has since eliminated many native forest birds from parts of the island and causes hundreds of electrical outages each year by climbing utility poles. In some areas of the U.S. territory, populations reach as many as 30,000 snakes per square mile.
That extraordinary expansion has long puzzled biologists. Guam’s population apparently began with only a small number of snakes, so extensive inbreeding should have reduced their capacity to adapt and limited their growth.
Hidden DNA changes may explain success
The snakes may carry far more genetic variation than earlier methods could detect, according to a University at Buffalo-led study published on July 24, 2026, in Science Advances.
Researchers from UB and the U.S. Geological Survey (USGS) used advanced long-read sequencing to examine large sections of the brown tree snake genome. They uncovered thousands of structural variants, including duplicated, deleted, and rearranged stretches of DNA, many of them concentrated in genes connected to immunity and smell.
This overlooked variation may help explain how a population established by only a few individuals survived a severe genetic bottleneck and became so successful.
“The brown tree snake is maybe not wildly diverse, but it has important sources of genetic diversity that have been underappreciated,” says the study’s corresponding author, Trevor Krabbenhoft, PhD, associate professor in the UB Department of Biological Sciences.
For agencies that have spent decades attempting to contain the snakes on Guam, the results may be discouraging. For conservation biologists, however, they suggest that endangered and inbred populations could retain more capacity to adapt than previously recognized.
“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 State University of New York Oswego. “We’re now getting a better understanding of unappreciated sources of genetic diversity that may explain how some inbred species can still respond to their environment.”
Long reads expose missing variation
Traditional assessments of genetic diversity often focus on differences in individual DNA letters, such as changing an A to a G or a T to a C. Early sequencing technologies largely restricted researchers to finding these single-base-pair differences.
Long-read sequencing can examine much larger sections of DNA and detect structural variants affecting at least 50 base pairs at a time. Across the genome, these large changes involve nearly eight times more DNA than single base-pair variations.
“It’s like looking at portions of two books letter by letter with a magnifying glass and thinking they’re the same, but not realizing entire paragraphs have been moved around or duplicated. Older sequencing technology didn’t allow us to easily see that DNA in one individual might be in a completely different place on the chromosome than in another,” says Levi Gray, PhD, a postdoctoral researcher in Krabbenhoft’s lab. “How we define genetic diversity and how we actually measure it is shaped largely by the technology of the day.”
Gray had previously investigated Guam’s brown tree snake problem while working with the USGS. That connection gave the researchers access to DNA provided by the USGS Brown Treesnake Rapid Response Team (RRT), which works to prevent the species from spreading elsewhere in the U.S. and its territories.
Immunity and smell genes stand out
Analysis in Krabbenhoft’s laboratory identified more than 19,000 structural variants in the brown tree snake genome. Each marks a location where stretches of DNA differ through duplication, deletion, or rearrangement.
The variants were not spread evenly throughout the genome. Instead, they appeared especially often in genes related to immune function and olfaction, the sense of smell.
Brown tree snakes depend heavily on smell to find food, using their forked tongues to collect chemical signals from the air. The unusual diversity in their olfactory genes may help explain a behavioral difference between populations. In their native range, the snakes sometimes eat other snakes, but there is little evidence of this behavior on 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,” Gray says.
The variants’ origins remain unknown
Researchers still do not know whether these structural variants existed before brown tree snakes reached Guam or developed afterward. Large-scale genomic changes usually build up across many generations, although some research suggests that severe population bottlenecks can speed their formation.
“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,” Gray says.
Reference: “Genomic structural variation rescues a classic biological invader from a population bottleneck” by Christopher A. Osborne, Brian M. Foote, Steven J. Fleck, Hannah M. Waterman, Sarah L. Chang, Melia G. Nafus, M. Renee Bellinger, Levi N. Gray and Trevor J. Krabbenhoft, 24 July 2026, Science Advances.
DOI: 10.1126/sciadv.aed3656
Funding was provided by laboratory startup funds to T.J.K. from the University at Buffalo.
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