Scientists have long pondered what drives crocodile evolution, and whether the climate or changes in sea levels are major factors in this evolutionary process. Now, a team of researchers from McGill University in Canada has found that, while changing temperatures and rainfall patterns had relatively little impact on the crocodiles’ gene flow during the past three million years, sea level changes during the Ice Age had a more significant impact.
“The American crocodile tolerates huge variations in temperature and rainfall. But about 20,000 years ago – when much of the world’s water was frozen, forming the vast ice sheets of the last glacial maximum – sea levels dropped by more than 100 meters. This created a geographical barrier that separated the gene flow of crocodiles in Panama,” explained study lead author José Avila-Cervantes, a research associate specializing in Genomics, Evolution, and Ecology at McGill.
According to the scientists, although crocodiles are very good swimmers, they are unable to travel long distances on land. By comparing the climate tolerance of living populations of American crocodiles (Crocodylus acutus) to the paleoclimate estimates for this region over the past three million years, the experts discovered that, since Caribbean and Pacific crocodile populations were isolated from each other during the Ice Age, they undergone different genetic mutations.
“This is one of the first times Ice Age effects have been found in a tropical species. It’s exciting to discover effects of the last Ice Age glaciation still resonate in the genomes of Pacific and Caribbean American crocodiles today,” said study senior author Hans Larsson, a professor of Biology at McGill.
“Discovering that these animals would have easily tolerated the climate swings of the Ice Age speaks to their resilience over geological time. Only humans in recent decades of hunting and land development seem to really affect crocodiles.”
These findings provide new insights into how environmental factors affect genetic evolution and thus where conservation efforts of specific crocodile populations in Panama should be focused.
The study is published in the journal Evolution.
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