The Evolutionary Ecology Momentum Research Group of ELKH’s Centre for Agricultural Research, led by Veronika Bókony and Edina Nemesházi, has developed a molecular diagnostic method that allows the determination of the genetic sex of agile frogs (Rana dalmatina). By applying the new method to domestic populations, it was found that some of the frog males in man-made habitats are genetically female.
In vertebrates with varying body temperature, environmental influences also affect, in addition to sex chromosomes, whether the developing individual has a male or female phenotype, so extreme temperature or chemical contamination can result in a sex change, i.e. a phenotype opposite to genetic sex. Examination of sex reassignment is also important in ecotoxicology and nature conservation, as it can lead to an unbalanced sex ratio that threatens the survival of populations. However, knowledge of the phenotypic sex (i.e., whether an individual has testicles or ovaries) is not sufficient to determine sex change, and genetic sex must also be diagnosed. The latter poses a major challenge for many groups of amphibians, fish, and reptiles, as their diverse sex chromosomes require finding a section of the genome for each species that allows genetic sex to be identified. In addition, it requires a significant investment of material and time to develop a method by which the sexing of a large number of individuals can be reliably carried out in practice. Due to these difficulties, such a procedure exists in only for a few amphibian species.
In a study published in the October issue of Molecular Ecology, the research team published a method for detecting the genetic sex of agile frogs from a small sample of DNA, such as mucosal tampon, using a simple and inexpensive laboratory method (PCR technique). Although this species is widespread in Europe, its populations are showing a declining trend, so it is also protected in Hungary. The field survey conducted with the new method showed that 20% of phenotypically male adults in the agile frog populations around Budapest had a female genotype, so they underwent a sex change at larval age. Of the 11 populations studied, sex-altered individuals lived primarily in urban and agricultural areas. These results warn us that chemical pollution, as well as climate change and the urban heat island effect, may lead to male predominance in the sex ratio of wild populations through sex reassignment. However, genetic sex determination methods can identify sex-altered individuals in a timely manner, which may help protect amphibian populations that are declining worldwide.