A new genetic study offers an explanation for how a small founding population of brown tree snakes became one of the world's most destructive biological invasions. University at Buffalo and U.S. Geological Survey researchers found more than 19,000 structural variants in the snakes' DNA, including duplicated, deleted and rearranged segments, according to findings published in the peer-reviewed journal Science Advances and highlighted on July 26.
Brown tree snakes are native to Australia and the South Pacific and probably reached Guam after the Second World War as stowaways in military cargo. Their spread drove several native forest bird populations to local extinction and continues to disrupt the United States territory's electricity network. USGS says climbing snakes cause hundreds of outages affecting thousands of residents, while densities in some areas have reached about 30,000 snakes per square mile.
The invasion presented a biological puzzle because only a few snakes are thought to have founded the Guam population. Such a bottleneck normally reduces genetic variety through inbreeding and can limit adaptation. The team used long-read sequencing, which detects large changes that older methods focused on individual DNA letters can miss. Structural variants affected nearly eight times more of the genome than single base-pair differences, the researchers reported.
The variants were especially common in genes associated with immunity and olfaction. Smell is crucial to snakes as they use forked tongues to collect chemical cues for navigation and hunting. Researchers said this overlooked variation may have helped the population survive inbreeding and respond to Guam's environment. It might also contribute to the observation that the snakes consume other snakes in their native range but show little evidence of cannibalism on Guam, possibly because smell helps them recognize close relatives.
The findings could change how scientists assess both invasive and endangered populations. Measuring only small DNA differences may underestimate the capacity of a genetically narrow population to persist or adapt, while long-read sequencing can expose larger rearrangements. That possibility is concerning for agencies trying to contain adaptable invaders, but it may offer cautious hope that some endangered, inbred species retain more evolutionary flexibility than conventional surveys suggest.
The study does not establish whether the structural variants were already present before the snakes arrived or developed after the invasion. Large genomic changes generally accumulate over many generations, although severe bottlenecks may accelerate some changes. The researchers said sequencing snakes from their native populations is the necessary next step. Until then, the work identifies a plausible genetic mechanism behind Guam's invasion without proving its timing or guaranteeing that the same pattern applies to other species.
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