How mites survived without sex for millions of years

Mites are capable of producing offspring without the aid of a partner. The children are exact replicas of their singular parent, creating a line of pure females.

This isn’t a scene from a science fiction novel, but a reality in the intriguing world of oribatid mites of the species Platynothrus peltifer.

Mothers give birth to daughters from fertile eggs that haven’t been fertilized by any male counterpart.

This process, known as parthenogenesis, gives rise to an all-female population – a peculiar characteristic that has caught the attention of scientists around the globe.

Asexual reproduction in mites

Scientists at the University of Cologne, along with their international colleagues, set out to investigate the remarkable asexual reproduction of oribatid mites.

The study revealed that the secret to the mites’ survival is in the independent evolution of their double chromosome copies – a concept known as the “Meselson effect.”

Through the use of genome sequencing techniques, the researchers identified several factors that contribute to the genetic diversity of the chromosome sets which could, in turn, ensure the mite’s long-term preservation.

Evolving chromosomes and genetic diversity

The oribatid mite is a living contradiction of the evolutionary principle, surviving over 20 million years without any trace of sexual reproduction.

These mites produce female offspring from unfertilized eggs, sidelining males to nonexistence or sheer rarity – thus, making no contribution to the gene pool.

In contrast to our understanding, the offspring inherit either all or some of the mother’s gene variants (alleles), turning into an identical copy of the mother.

Interestingly, the mite’s two chromosome sets evolve independently, allowing the introduction of new genetic variants while preserving essential information.

These changes enable rapid adaptation to environmental fluctuations, providing a selective advantage.

New tools in the genetic toolbox

The research highlights horizontal gene transfer (HGT) as another mechanism that enhances genetic diversity. HGT refers to the exchange of genetic material outside the boundaries of sexual reproduction.

From a metaphorical perspective, horizontal gene transfer is similar to adding new tools to a preexisting toolbox.

“Some of these genes seem to help the mite to digest cell walls, thus expanding its food spectrum,” noted study lead author Dr Hüsna Öztoprak, an expert in the Institute of Zoology at the University of Cologne.

The role of “jumping genes”

Transposable elements (TEs), or ‘jumping genes,’ also play a significant role. They are dynamic components of the genome, exerting influence by altering their locations, akin to rearranging chapters in a book to change the plot’s trajectory.

The excitement lies in the different activity levels of TEs in the two chromosome copies. One copy demonstrates an active state that allows for dynamic transformations, while the other remains relatively inactive.

The findings of the study add significant value to understanding the survival strategies of asexual organisms.

“In future research projects, we would like to find out whether there are additional mechanisms that might be important for evolution without sex,” said Dr. Jens Bast, Emmy Noether group leader at the University of Cologne.

Mites and evolutionary adaptation

The study of oribatid mites offers a fascinating glimpse into how organisms can adapt and thrive without sexual reproduction, challenging long-standing evolutionary theories.

While sexual reproduction is traditionally seen as essential for maintaining genetic diversity and evolutionary fitness, these mites demonstrate an alternative path.

Their ability to evolve through mechanisms such as the Meselson effect, horizontal gene transfer, and transposable elements suggests that asexual reproduction can still provide the necessary genetic variation for adaptation.

This discovery could inspire further research into other organisms that rely on similar strategies to survive in challenging environments, potentially offering new insights into evolutionary biology.

Implications for biodiversity and conservation

Understanding the genetic mechanisms behind the asexual reproduction of oribatid mites could have broader implications for biodiversity and conservation efforts.

These mites play a crucial role in soil ecosystems by aiding in decomposition and nutrient cycling.

Insights into their genetic resilience could inform conservation strategies for other asexual or endangered species facing environmental pressures.

Additionally, studying the ability of oribatid mites to adapt without genetic recombination may offer practical applications in agriculture and pest management, as scientists seek to harness or mitigate similar reproductive strategies in other organisms.

The full study was published in the journal Science Advances.

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