Evolution Update

Evolution Update

Captive Breeding in Crocodiles and Points to a Way For Their Survival

Christopher Jenness March 21, 2015

The Cuban crocodile is critically endangered, but to what extent is the captive breeding program in Cuba helping prevent their potential extinction?

The Cuban crocodile (Crocodylus rhombifer)is an aggressive species of crocodile found in Cuba. Although it was once found throughout the Caribbean, the Cuban crocodile is now limited to just the Zapata Swamp in Cuba. Their declined population has caused the International Union for Conservation of Nature to classify them as critically endangered.

Much of the decline of the Cuban crocodile is attributed to human hunting activities. Additionally, their habitat has been modified by humans over time, making them less able to survive and reproduce in their native environment. As the Cuban crocodile nears extinction, their small population size causes a new hurdle to their success as a species.

The small population of Cuban crocodiles shares a habitat with a much more abundant species of crocodile, the American crocodile. This poses an additional threat the Cuban crocodile: hybridization. Hybridization occurs when two closely related species produce offspring. Usually, this is a good thing for the survival of species, but in this specific case, it can be very detrimental to the Cuban crocodile. Because the American crocodile is very abundant, the chance of hybridization is high and the hybrid offspring do not contribute to the prosperity of the Cuban crocodile. This combination can allow the American crocodile and the American-Cuban hybrid populations to overtake the Cuban crocodile.

In order to protect the Cuban crocodile, a captive breeding program was established in 1959. By capturing a few hundred crocodiles from the Zapata Swamp, conservation biologists hoped to prevent extinction by breeding the Cuban crocodile in captivity. This programed has largely been a success. Today there are over 4000 crocodiles in the breeding facilities which have been breeding for over ten generations.

But how successful has the captive breeding program been in preventing hybridization between the Cuban and American crocodile species? A recent study by scientists at the Universidad de La Habana and the University of British Columbia looked at this problem by examining the levels of hybridization in natural and captive populations of crocodiles in Cuba. By looking genetic data from the two species of crocodiles, the scientists were able to get an idea of how much hybridization was threatening the extinction of Cuban crocodiles.

What they found was striking: a large percentage of natural and captive crocodiles are hybrids. In the wild, nearly 50% of crocodiles sampled in the Zapata Swamp were a result of hybridization. In captivity, where the goal is to avoid hybridization altogether, 16% of crocodiles were hybrids. While this means the captive breeding program is doing a better job of elimination hybridization than in the wild, there is still a long way to go to avoid hybridization completely in captivity.

Even though these numbers are alarming, the study also provided insight into how to protect the Cuban crocodiles going forward. These numbers indicate that the captive breeding program needs to make a better distinction between Cuban and American crocodiles when forcing breeding events. More importantly, this study identified a small subset of Cuban crocodiles that the scientists termed “genetically important.” These crocodiles are very genetically diverse and likely to produce offspring capable of repopulating Cuban crocodiles in the wild.

Moving forward, this study raises concerns, but hopefully can provide a path to avoid extinction of the Cuban crocodiles. If used correctly, the data in this study could have a lasting impact on the biodiversity in Cuba and throughout the Caribbean.

Recent Articles

"Why Do Those Flowers Look like Bugs? Or, on the Evolution of Orchids."
A large group of flowering plants, commonly known as Orchids, often have flowers whose shape coincides with that of their insect pollinators. Recent research has shown how this uncanny flower morphology is guided by evolutionary selection.

"How Plants Maintain a Low-Sodium Diet Without Advice from Their Doctors"
Salt tolerance is a critical stress response in many plants and is controlled by a wide variety of interacting genes. Researchers studying sodium transporters in trees from high-salinity environments have characterized the evolution of these genes and determined that they are under strong positive selection in salty soils.

"Evolutionary History of a Widespread, Recently Diverged Antioxidant Enzyme in a Pig Pathogen"
Peroxiredoxins are proteins conserved across all domains of life that protect cells against the threat of reactive oxygen species. Researchers have recently characterized the evolutionary history of an essential peroxiredoxin gene from a common livestock pathogen.

"A New Class of Antibiotics Less Susceptible to Evolutionary-Driven Resistance Development"
Pathogenic bacteria are evolving resistance to our antibiotics at an alarming rate, however, scientists have recently discovered a molecule that may help combat these microscopic killers.