The Orinoco crocodile, Crocodylus intermedius, is one of the most threatened crocodile species in the world. There are now just a few wild populations remaining in Venezuela and Colombia. Excessive hunting until the 1960s and egg collecting for their local consumption decimated their numbers, and now new conservation efforts are aiming to revive their dwindling population numbers.
One such effort involved the reintroduction of one population by an international team of researchers led by Natalia Rossi Lafferriere from Columbia University, and can be found at the La Ramera lagoon at the El Frío Biological Station, Venezuela. I can’t imagine a better job than rearing endangered crocodile eggs for the purpose of reintroducing them into the wild when they were ready!
But how do you work out if reintroducing endangered species like this is a successful venture or not?
To test this, the team sampled 20 egg clutches (335 hatchling micro-crocodiles) for incubation in their laboratories, and were able to conduct genetic analysis on them in order to test to see who their fathers were. This is important as you can get a measure of genetic diversity within populations, which is a vital factor in whether or not populations have the capacity to survive. It’s probably also important to do this via genomic analysis rather than observation for what I’d think were obvious reasons.
What did they find?
Perhaps unexpectedly for humans, but quite expected for wild animals, the research team discovered that half of the egg clutches were actually fathered by more than one male! Of the 14 fathers inferred from genetic analysis, they found that only 6 contributed to a whipping 90% of the total offspring. Even more bizarrely, 3 of these 6 males fathered more than 70% of the total number of offspring. Full points for productivity to those chaps!
The evolution of females mating with multiple mating is known as polyandry, and can be achieved either through mating with multiple individuals during the same reproductive season, or actually storing sperm in the reproductive tract for later fertilisation.
This activity has rarely been observed in captive population of crocodiles, but has been documented in the wild for American alligators and the spectacled caiman, suggesting that multiple mating systems might be widespread in crocodilians and an important factor in their survival. These beasties and their ancestors have been around since a time around the origin of dinosaurs, after all!
These new results reveal the first evidence for multiple paternity in a reintroduced Orinoco crocodile population, and therefore supports the success of reintroduction efforts for this species.
Why is this important?
More than half of the living species of crocodilian are endangered, thanks to threats to habitat change, human disruption, and ongoing environmental changes. By gaining an insight into their reproductive behaviour, we can learn more about how to reintroduce these animals into the wild into sustainable populations.
In this case, multiple paternity might be important part of mating systems for increasing the overall genetic diversity in populations, as well as the total size of populations. These factors are often critical in maintaining flexibility and diversity in populations, and they play an important role in survivability at a population level, something that is becoming increasingly crucial for these endangered animals.
Other benefits of this can include sharing resources with mothers to ensure greater offspring survival, and greater selection of ‘higher quality’ mates, which is important for that well known concept of survival of the fittest. Darwin would be proud!
Successful reproduction is a vital and necessary first step in the recovery of the Orinoco crocodile. This is an excellent example of a successful reintroduction effort of a critically endangered species, and hopefully a sign that we can reverse the effects that led to their endangerment before it’s too late.
Continued conservation action will be important to mitigate ongoing threats to the Orinoco crocodile. This includes banning poaching, protecting their habitats, and will require a combined effort from governmental conservation authorities in order to create sustainable initiatives.
All is well that ends well too, and all crocodiles were released back into the wild as juveniles. Life, er, finds a way!
The article is published in the open access journal PLOS ONE.
Rossi Lafferriere NA, Antelo R, Alda F, Mårtensson D, Hailer F, Castroviejo-Fisher S, et al. (2016) Multiple Paternity in a Reintroduced Population of the Orinoco Crocodile (Crocodylus intermedius) at the El Frío Biological Station, Venezuela. PLOS ONE 11(3): e0150245. doi:10.1371/journal.pone.0150245