The brown tree snake is considered one of the most notorious invasive species in the world. Originally from Australia and the southern Pacific, this species is believed to have been introduced to the island of Guam after World War II, likely arriving aboard military transport planes. The arrival of the brown tree snake on Guam led to the extinction of many native forest bird species and causes hundreds of power outages each year, as the snakes climb onto power poles and equipment. In some areas, snake populations have reached up to 30,000 individuals per square mile.

Genetic Diversity and Adaptation

For a long time, biologists have tried to understand how the brown tree snake population on Guam, which started from a small number of individuals, was able to spread so rapidly. Typically, limited genetic diversity reduces a population’s ability to adapt and lowers the chances of rapid growth due to inbreeding.

However, a recent study using advanced long-read DNA sequencing methods revealed that brown tree snakes possess much greater genetic diversity than previously thought. Scientists discovered thousands of structural variants in the snakes’ genome, including duplications, deletions, and rearrangements of DNA segments. Many of these changes were concentrated in genes related to immunity and the sense of smell.

The Importance of Structural Variants

Most previous knowledge about genetic diversity was based on studying changes in individual DNA base pairs. Early sequencing methods were effective at detecting small changes but could not identify large differences affecting long stretches of DNA. Modern long-read sequencing technologies now allow researchers to study larger, continuous sections of the genome, revealing structural variants that alter the genome up to eight times more than point mutations.

Analysis of samples found over 19,000 structural variants, indicating significant genetic diversity. These variants were especially common in genes responsible for immune function and olfaction. Brown tree snakes rely heavily on their sense of smell for navigation and finding food, collecting chemical signals from the air with their forked tongues.

Behavioral Traits and Evolution

The unusual diversity in olfactory genes may help explain some behavioral traits of these snakes. In their native range, brown tree snakes are known to prey on other snakes, but on Guam, cases of cannibalism are rare. Enhanced olfactory abilities may allow snakes to recognize each other as relatives, especially in a population with high inbreeding, reducing the likelihood of cannibalism.

Scientists have not yet determined whether these structural variants appeared before the snakes arrived on Guam or developed after the invasion began. Typically, large genomic changes accumulate over many generations, but some studies suggest that genetic bottlenecks can accelerate the development of structural variants.

Implications for Invasive Species Management

The discovered genetic diversity may complicate efforts to control the brown tree snake population on Guam, as high genetic flexibility makes the species more resilient. At the same time, these findings offer hope for endangered species with small or inbred populations, since hidden sources of genetic diversity may help them adapt to their environment.

To accurately determine when these structural changes appeared, comparisons with brown tree snake populations from their native range will be necessary.