They have ovaries, but also testosterone-producing testicular tissue: What is behind this masculinization in female moles, researchers have now discovered. Accordingly, in the development history of these animals, restructuring in the genome caused the effect of intersexuality. This emerges from investigations of the now sequenced genome of the strange mammals. Presumably, the high testosterone level gives the mole ladies a kind of doping effect during their hard work underground.
The land, the water and the air are the typical habitats of most animals – but some have also conquered the earth. The most prominent representatives of the animal miners are the moles. The various representatives of the Eurasian moles (Talpa) are fascinatingly adapted to life underground: in search of insects and worms, they dig their way through the earth with their powerful grave shovels. Both sexes have exceptionally strong muscles. The females are not only as strong as the males – they also have other amazingly masculine characteristics.
As is typical of mammals, although they are equipped with two X chromosomes, they still have functioning ovarian and testicular tissue in an organ called Ovotestes. The testicular tissue of female moles does not produce sperm, but does produce large amounts of the sex hormone testosterone, so that the females have similar levels to the males. Presumably this leads to a natural doping effect: the hormone makes the female moles muscular and possibly more aggressive, which is helpful in their digging and the fight for resources. Obviously, genetic peculiarities developed in the evolutionary history of these animals that led to this form of intersexuality – but which ones?
Tracking down the genetic basis
An international team of researchers has now investigated this question. “At some point, sexual development in mammals usually continues in one direction or the other – male or female. We wanted to know how evolution modulates this actually established process and enables the intersexual properties of moles, ”says co-author Darío Lupiáñez from the Berlin Institute for Medical Systems Biology. As part of their study, the scientists first sequenced and analyzed the genome of the Iberian mole Talpa occidentalis.
By comparing the genomes of other animals and humans, the researchers discovered a so-called inversion in the moles. It is an upside-down section of genetic material in an area that is involved in the formation of the testicles. As they explain, the rotation brings additional DNA segments into the regulatory area of the gene called FGF9, which causes an altered activity. “This change leads to the fact that testicular tissue can develop in female moles,” says the lead author of the study, Francisca Martinez Real from the Max Planck Institute for Molecular Genetics in Berlin (MPIMG). The team also found a triple genome section around the gene CYP17A1, which is responsible for the production of male sex hormones. “The triplication creates additional control sequences for the gene – and in the ovotestes of the female moles, more male sex hormones are produced, especially more testosterone,” says Real.
Doping for work underground
The scientists then confirmed through studies on mice that CYP17A1 is actually linked to the masculinization of female moles. They developed breeding lines of the animals to which they transferred the genetic trait of the mole. It was found that the females of these test animals also had an increased level of male hormones that was as high as that of normal male mice. This made the females much stronger than unchanged conspecifics, the researchers report. Apparently this is an effect that leads to a survival advantage for the mole ladies and has thus established itself. In the case of the moles, the sexes are therefore not as clearly delimited from one another as in other mammals.
“Our findings are a good example of how important the organization of the genome is for evolution,” says Lupiáñez. “Nature makes use of the existing toolbox of developmental genes and only rearranges them in order to create a characteristic such as intersexuality. Other organ systems and development are not affected, ”says the scientist. Co-author Stefan Mundlos from the MPIMG concludes: “There was and is the tendency to characterize intersex phenotypes as pathological conditions. Our study shows how complex sexual development is and that nature can produce a wide range of intermediate types, ”says the scientist.
Source: Max Planck Institute for Molecular Genetics, specialist article: Science, doi: 10.1126 / science.aaz2582