Sex is considered the central engine of evolution. But not for the horn mite: it continues to plant in an inexhaustible – and for more than 20 million years. How does this arachnid manage to provide genetic diversity without sex? A study has now discovered several mechanisms for this. Accordingly, the two chromosome rates of the horn mite can develop independently of one another. This creates a scope for evolutionary innovations. Genetic expression is also flexibly regulated and “jumping genes” ensure genetic innovations. In addition, the mite takes up new gene material from its environment.
In the case of sexual reproduction, the genetic material of both parents is newly combined. In this way, species secure their genetic variety, which enables them to adapt flexibly to new environmental conditions. “According to the scientific consensus, sex is a prerequisite for long -term evolutionary survival,” explains a team around Hüsna Öztoprak from the University of Cologne. Because without the mixing of the genetic material, genetic stagnation and thus in extreme cases threaten to die out.
Independent chromosome rates
“But some asexual species survive the time and thus contradict the consensus. How you escape this dead end is puzzling, ”said Öztoprak and her colleagues. The research team has now taken a closer look at one of these species: the horn mite Platynothrus Peltifer. For at least 20 million years, the females of this kind have laid out unfertilized eggs, from which new females hatch, which also reproduce unexpectedly. Males do not occur in the entire reproductive process. Aner how do the mites manage to maintain a high genetic diversity and to remain evolutionary?
Using gene novelsalyzes, Öztoprak and their team have now tracked down the secrets of the horn mite. Accordingly, the key to evolution without sex lies in the fact that the two chromosome copies of a horn mite can develop independently of one another. This creates differences between the gene copies over time that enable new combinations. This phenomenon is known as a Meselson effect and ensures that new genetic variants can arise even without sex.
Evolutionary experiments with backup solution
As the researchers found, the regulation of gene expression plays an important role. If there is a mutation in one of the two chromosome sets, the other chromosome set serves as a backup with the proven variant. If the new mutation is not advantageous, the original version is read and the mite has no disadvantage. However, if the new mutation offers an advantage – for example to adapt to a change in the environment – the mutated variant becomes active and the mite provides a selection advantage. The situation is similar with “jumping genes”, also known as “transposable elements”. These DNA sections can change their position within the genome and thus also create variations. They are different in the two copies of the chromosome set.
Another trick of the horn mite for more diversity is the so -called horizontal gene transfer. New genetic material from the environment is absorbed and integrated into your own genome. These DNA pieces can come from bacteria or viruses, but also from plants or other animals. “Horizontal Gentransfer, in which even genes from non -species organisms can be transferred, works like adding new tools to an existing tool box,” explains Öztoprak. “Some of the genes acquired in this way seem to help the mite, for example, to digest cell walls and thus expand their food spectrum.”
From the point of view of the researchers, the asexual horn mite is an interesting evolutionary exception, which can help to better understand the advantages and disadvantages of sexual and asexual reproduction. The study provides an insight into how asexual species also provide genetic diversity and can thus secure their continued existence in the long term. “In future research projects we would like to find out whether there are other mechanisms that are important for evolution without sex,” says Öztoprak’s colleague Jens Bast.
Source: Hüsna Öztoprak (University of Cologne) et al., Science Advances, Doi: 10.1126/sciadv.adn0817