14 DAY TRIAL // In humans and mammals, sex determination is chromosomial: the male gender is determined by the presence of a male Y chromosome next to an X chromosome, while a double set of X chromosomes determines the development of females.
But this is not general: in other animal groups, this in determined by particular genes, or even by temperature during the incubation of the eggs, that activates or inhibits the malehood genes.
This is the case of reptiles, at least turtles and crocodiles, and due to the current global warming, this can prove tricky. In reptiles, cooler nesting temperatures induce the development of males while higher nesting temperatures provoke the development of females.
A team at University of Exeter found that North American marine turtles are under threat if the global warming occurs at the predicted levels: a rise of just one degree Celsius above the current temperature would wipe out entirely the emergence of male turtles from some beaches.
An increase of three degrees Celsius would inflict severe levels of hatchling mortality and reduction in US nesting beaches.
This study used data from 26 years of loggerhead turtle nesting and climate changes in predicting patterns for future warming. Nest temperatures must be at the right mean level for eggs to develop healthily and hatch successfully in an equilibrated sex ratio. "We are stunned by these results and what they could mean for the species in the future,' said Dr Brendan Godley of the University of Exeter's School of Biosciences."
"In particular, we're concerned that populations that are already predominantly female could become 100% female if temperatures increase by just one degree. This is a major issue for nesting populations further south, in Florida, for example, where males are already in short supply."
The researchers found that in the warmer Florida, 90% of hatchlings are female, while in cooler North Caroline 42% are male and some of these males currently travel south, equilibrating southern populations.
If the northern Caroline populations are hit by the global warming, this fragile equilibrium could go away. "We take this as an important step in identifying essential thermal habitat for marine turtles," said study co-author Dr. Matthew Godfrey, of the North Carolina Wildlife Resources Commission. "It highlights the need to establish measures to specifically protect male-producing beaches."
"In the face of climate change, it's essential that we prioritize the protection of sites that produce males not only for local breeding success, but to help support potentially vulnerable populations further south", said Dr Brendan Godley.