It may sound like the beginning of a cheesy horror movie, but crocodile species actually do naturally hybridize in the wild. Hybridization is generally considered a threat to most animals, as it creates individuals with reduced fitness—meaning they are unable to reproduce. In Mexico and Belize, it has been hypothesized that American and Morelet’s crocodiles have been hybridizing due to sightings of crocodiles that have a mix of physical characteristics from both species. In a new paper in Royal Society Open Science, Evon Hekkala of Fordham University and colleagues investigate the causes of this hybridization in Belize.


Morelet’s crocodile

The team conducted their study on the two aforementioned crocodile species in southern Belize, investigating physical characteristics of eggs, nests, and the crocodiles themselves. Crocodiles were captured at night using spotlights, dip-nets, and noose-poles. But the fun didn’t stop there—nest mounds were examined up close and personal. It had been noted that there were some odd looking nests, so researchers went into the nest mounds to measure them and take out one egg for study.

DNA analysis from both the crocodiles and their eggs made it clear hybridization between the American and Morelet’s crocodile was occurring in Belize. In addition to DNA evidence, morphologically intermediate characters were found on some of the crocodiles that were captured and measured. The atypical nest mounds were also physically ambiguous and possessed characteristics from nests of each species—indicating they were likely made by hybrid crocs. Interestingly though, the study of the eggs of these crocodiles indicated that the fitness of the hybrids was not reduced compared to the “pure” species. Only 5% of the hybrid crocodile eggs were not viable, while around 8% from each pure species were considered not viable.

Although this might not prevent the crocodiles from reproducing, hybridization still damages biodiversity. Lead study author Evon Hekkala explains: “Our data on patterns of hybridization in Caribbean crocs suggest that combined climate change and human land use patterns may be influencing the breakdown of species barriers in protected crocodile species, which could potentially result in a loss of biodiversity over time.”


The American crocodile

It is possible that coastal development of Belize is reducing the preferred habitat of American crocodiles and causing them to seek out new territory. This increases the chances of overlap with populations of Morelet’s crocodiles. Coastal land development for tourism purposes is extremely common in this area of the world. This will potentially cause the loss of the rarer, more vulnerable crocodile species—the American crocodile. The goal of most conservation programs is to preserve a genetically pure population, so understanding hybridization and why it occurs is vital. If humans are impacting specific populations of crocodiles in Belize and causing them to hybridize, it must be resolved to preserve the integrity of these two species.

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