Among crocodilians, Crocodylus rhombifer (shown here) is one of the world’s most endangered species with the smallest natural distribution. In Cuba, the species coexists with the American crocodile (Crocodylus acutus).
Credit: Stave Zack/Wildlife Conservation Society.
Two different crocodile species living in Cuba have been shacking up, producing hybrid offspring that have now been identified with genetic analyses. The interbreeding could threaten one of the species, the already declining Cuban crocodile, researchers say.
Scientists were aware that the American crocodile (Crocodylus acutus) and Cuban crocodile (Crocodylus rhombifer) interbred in captivity. But this is the first genetic study to confirm hybridization in the wild.
The researchers found that American crocodiles living in Cuba are more closely related, genetically, to Cuban crocodiles than to American crocodile populations found along mainland Central America.
Researchers analyzed the DNA of scales clipped from the tails of 89 wild-caught Cuban and American crocodiles from Cuba, Central America (Costa Rica and Panama), Grand Cayman Island and Jamaica. Two of the samples came from North American zoos. [10 Species You Can Kiss Goodbye]
Because the researchers included mitochondrial DNA, which is passed down from mothers, they could tell that the hybrid offspring had come from a matchup between male C. acutus and female C. rombifer.
The team thinks this scenario makes sense for the place in Cuba where the hybrids were found, the Zampata swamp. For one, there is a two-month overlap in the courtship and mating period for both species in that swamp. Second, in the area where the two species come into contact, there are more C. acutus individuals, giving these male American crocodiles more opportunity to mate with other females, which are known to take more than one lover.
The researchers warn that the two crocodile species interbreeding in the wild may pose a major threat to Cuban crocodiles. In a worst-case scenario, one crocodile lineage can cause the extinction of another.
Due to habitat modification and extensive hunting from the mid-19th century through the 1960s, the population of Cuban crocodiles has drastically declined. Although the exact population of the species remains unknown, scientists estimate that at least 3,000 remain in the Zapata swamp, with a smaller population residing in the Lanier Swamp on the Island of Youth.
The researchers urged that human-related causes of hybridization be taken into account in any plans to conserve the dwindling Cuban crocodile population.
The study is detailed in the spring issue of the Journal of Experimental Zoology.