Among the problems of climate change there is no gender identity crisis … At least for us. But, unlike humans, for some reptiles (such as crocodiles and sea turtles) the question is serious: the sex of the unborn is determined by the temperature during the incubation process. Higher temperatures produce more females: scientists have been trying to figure out how this happens for 50 years, and now a team of Australian researchers think they have the answer.
It was believed that sex determination was cause or environmental or genotypic. However, a few years ago, Australian researchers questioned the theory showing that both of these factors are involved in determining the sex of the bearded dragon (Pogona), a reptile of the Agamidae family, who inherit the sex chromosomes from both parents, such as the human beings. In their case they receive a combination of chromosomes Z and W, instead of X and Y: males have the combination ZZ, females ZW. Raising the temperature above 33 ° C during incubation, female specimens come out of all the grapes. In fact they remain genetically male (ZZ), but with functional female parts that can make them mate and lay eggs.Males and females:
can mammals also choose? Snow skink (Niveoscincus ocellatus), another Australian reptile that changes sex according to the climate (see). | Msayers / WikiMedia
The eggs of these genetically male females will certainly have the ZZ chromosome and this process leads to the progressive elimination of the W chromosome, which means that the offspring could become all genetically male but sexually determined by temperature. A potentially disastrous result for these reptiles: the temperature increase caused by climate change would lead to a female-only population, and therefore to extinction.
Discovered the mechanism of the sex switch, Clare Holleley and his colleagues hypothesized that the key to the genetic mystery could be found in a biological switch involved in the protein production process. They therefore focused research on messenger ribonucleic acid (mRNA) that carries DNA with instructions on how to build proteins that contribute to genetic traits in the ribosome, including sex. The researchers decided to compare the messenger RNA molecules produced by the "obliged" females with those produced by normal males and females.Fish that change sex
"We found out that hot female ones produce a unique message: their ANN holds a piece of gene sequence normally attached to the message, " explains Ira Deveson, co-author of the study. "This means that the gene will not give rise to a normal protein." A similar mechanism (ie a portion of the message held by RNA) has also been found in crocodiles and turtles, which suggests that it could be responsible for determining sex through temperature for all saurians.
"We think the discovery can pave the way for a completely new approach to understanding how males and females differ in all animals, " says geneticist Jenny Graves, of the University of La Trobe (Australia): "in nature there are many ways in which males and females differ, this shift drives us all one step closer to understanding the whole picture of sexual differentiation. "