Mad Science.
The latest cool reptile research from around the globe.
This instalment features two items with titles reminiscent of
‘Six Degrees of Separation’:
Bodybuilders, Fish Farms and Costa Rican Crocodiles.
Based upon claims of a disproportionate number of males amongst American Crocodiles (Crocodylus acutus) in and
around the Palo Verde National Park in Costa Rica, in 2012 researchers began a three-year project to capture and
identify the gender of as many crocs as possible.
Working at night, in smothering heat and difficult conditions, the team was often compelled to wade into the water to
catch the crocs, which can measure more than two metres in length. Sexing is relatively straightforward once the
animal has calmed down, and involves probing the cloaca with a finger. If a structure is felt, it is a male; the lack of
any structure indicates a female. Small juveniles are more problematic, and were taken back to the research station for
conclusive examination.
A sample of 474 crocodiles, taken from seven different sites, yielded a ratio of about 3.5 males for every female, with
males comprising about 60% of adults and nearly 80% of hatchlings. The results were particularly surprising, given
that climate change should be skewing the sex ratio in the opposite direction. Crocodilians lack sex chromosomes, and
instead gender is determined by incubation temperature. Mean minimum temperatures have risen approximately 2.5 o C
in Palo Verde in the last 20 years, and after measuring crocodile nest temperatures, the research team concluded that
on this basis alone, female hatchlings should outnumber males by a factor of nearly two to one.
Crocodilians, like this Saltwater Crocodile (Crocodylus porosus) lack sex
chromosomes, and instead gender is determined by incubation temperature.
Image by Michael Cermak.