Researchers at the National Research Council (CSIC) identified the molecular mechanism that links the increase in temperature with the inhibition of aromatase, an enzyme that converts androgens to estrogens.
"In many species of vertebrates, mainly fish and reptiles, the temperature influences sex determination of individuals," says Francesc Piferrer, expert at the Institute of Marine Sciences, CSIC.
"This influence is more emphasized in some cases, the fact that there is more or less heat is imposed over the genetic information written in DNA," he adds. For example, sex determination for sea bass depends on the combination of genetic and environmental factors.
Previous studies proved that it is possible to have a sea bass population with a similar percentage of males and females and to get 100 per cent males as a result of increased temperature. "The most intriguing was that environmental factors had their greatest impact in a development moment in which the gonads were not only different, but had not yet begun to form," says the scientist.
During the investigation, whose results were published in the journal PLoS Genetics, two groups of sea bass larvae were exposed to different temperatures, normal and high.
"The results show that temperature increase leads to DNA methylation of the promoter of the aromatase gene (called cyp19a), which is tantamount to silencing by blocking transcriptional activation," said Piferrer. In the study group there were females with partially inhibited aromatase and were developed as females.
"However, Piferrer adds, in other females of the same group the aromatase inhibition had affected them at a higher level, and they had become males."This research allows the description of the operation of an epigenetic mechanism between environmental and the cell factors for the first time, leading to sex determination of a specimen.
At other times, it had only been documented a similar mechanism in plants. This study, which included the collaboration of the Centre for Genomic Regulation in Barcelona, also clarifies why many farmed fish are males.
"The explanation is that, in trying to accelerate growth, farmers grow the larvae at elevated temperatures," says Piferrer. "Sex determination by temperature is very common in reptiles and it will be interesting to see whether a similar mechanism is also present in fish," says the scientist.