Genetic Evolution and the Ice Age: What Crocodile DNA Reveals

Environmental factors such as sea level influence genetic evolution and show where conservation efforts can focus. What drives crocodile evolution? Is climate or sea level change the main factor? Determined to answer these questions, researchers at McGill University have discovered that while changing temperatures and precipitation over the past three million years have had little effect on crocodile gene flow, sea level changes during the Ice Age have had a different effect.

“The American alligator tolerates large fluctuations in temperature and precipitation. But about 20,000 years ago – when most of the world’s water was frozen and formed the vast ice sheets of the last glacial maximum – sea levels dropped more than 100 meters. José Ávila, a PhD student working under the supervision of McGill professor Hans Larsson “This created a geographic barrier that isolated the gene flow of crocodiles in Panama,” says Cervantes.

Researchers note that crocodiles are good swimmers, but cannot travel long distances on land. As a result, Caribbean and Pacific crocodile populations became isolated from each other and as a result underwent different genetic mutations.

The team compared the climate resilience of living populations of American alligators (Crocodylus acuteus) is a period of extreme climate fluctuations during the Ice Age, with paleoclimate estimates for the last 3 million years for the region.

“This is one of the first cases in which ice age effects have been detected in a tropical species. It’s exciting to find that the effects of the last Ice Age’s last glaciation are still reflected in the genomes of Pacific and Caribbean American crocodiles today,” says Larsson, professor of biology at McGill University’s Redpath Museum.

“The discovery that these animals can easily withstand the climatic fluctuations of the Ice Age suggests that they persisted through geological time. In recent years of hunting and land development studies, only humans seem to really affect crocodiles,” he says. The findings provide new insights into how environmental factors affect genetic evolution and where conservation efforts should focus for individual crocodile populations in Panama.