Cuban crocodiles near extinction; inter-breeding with other species main reason

Study finds breeding between Cuban and American crocodiles is more extensive than thought earlier

By DTE Staff
Published: Tuesday 09 December 2014

A Cuban Crocodile

A study conducted by a team of Cuban and Canadian researchers has found that the Cuban Crocodile—the most endangered species of crocodilian in the world—is fast hurtling towards extinction as it loses its genetic purity due to interbreeding with the American Crocodile, another crocodile species also found on the Cuban island.

The team was led by Yoamel Milián-García of the University of Havana. Its findings were published on October 22 in the journal Heredity.

Just 4,000 of them left

The Cuban crocodile, which was once found all across Cuba and the West Indies, is today found in just two areas – the Zapata swamp on the main island of Cuba and Isla de la Juventud, the nation’s second largest island. The total population is just 4,000 individuals.

The team analysed genetic markers from the scale clippings of 227 wild crocodiles and 137 crocodiles from the Zapata Swamp Captive Breeding Farm. The results showed the level of hybridisation in the wild was much higher than previously believed—49.1 percent of the wild crocodiles sampled were hybrids, while just 16.1 percent of the captive crocodiles had mixed genes.

According to a report in the journal The Scientific American, the results mean that in each baby crocodile born, a portion of the Cuban crocodile genome is being replaced by American crocodile genes. With each subsequent generation, more and more Cuban genes are being lost, and eventually the species could go extinct.

The Scientific American report said the loss of genes the Cuban crocodile has the potential to reduce the species’ ability to adapt to environmental challenges it may face.

Milián-García, who led the study, was quoted in the report as saying that the next step was to determine whether the hybridisation of the two species was a natural phenomenon or not. “We have been seeing it has a natural component and could be enhanced by anthropogenic pressures. But it’s critical for us to determine the magnitude of each component in this process,” said Milián-García.

The report noted that the issue was further complicated by evidence that American crocodiles in Cuba were actually more closely related to the Cuban crocodile than to other American crocodiles found on the mainland of the Americas. It appears that in the Caribbean, American crocodiles took on some genes from their Cuban relatives a little more than two hundred thousand years ago. That implied there were three distinct genetic groups rather than two.

“We don’t know if that’s ancient hybridization or a more complex sort of evolutionary phenomena,” George Amato, director of the Sackler Institute for Comparative Genomics at the American Museum of Natural History told the Scientific American. “But we feel pretty confident that the current observed hybridisation is a threat to what we recognize as a distinct species.” Amato was not involved with the recent study but is familiar with the work.

The report said that there were some hopeful signs in the genetic analysis of the captive Cuban crocodiles. Approximately 30 per cent had a unique subset of genes—DNA they did not share with the rest of the captive population. That made them valuable reservoirs of Cuban crocodile DNA, and it could be used to help the entire population maintain genetic diversity in the face of the American crocodile onslaught. Researchers planned to use the information to help design Cuba’s first formal attempt at a scientifically informed crocodile management plan.

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