Reproduction Can humans reproduce without sex

How to survive without sex

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The little rotifer Adineta ricciae can do without sex.
The little rotifer Adineta ricciae can do without sex.
© Natalia N. Pouchkina-Stantcheva
© Natalia N. Pouchkina-Stantcheva

Why do almost all organisms reproduce sexually? If it were only about numbers, sex would have long since disappeared from the picture or would not have arisen in the course of evolution. Measured in terms of reproductive success, sexual reproduction is far inferior to asexual ones, which renounce the production of non-reproductive males. But sexual reproduction leads to greater genetic variability - that is its great advantage. Paternal and maternal genes are recombined in the offspring; positive mutations can thus be merged, negative mutations can be covered. Genetic variability is therefore an "insurance" for the future: Within a population there will always be individuals who are better adapted to changing environmental conditions than their conspecifics and thus ensure the survival of the species.

The offspring of asexual reproduction, on the other hand, are genetically identical, they are clones of their mother. Their adaptability to changing environmental conditions is difficult due to the lower genetic variability. Numerous asexually reproducing organisms therefore repeatedly insert a sexual reproductive cycle, such as the water fleas, for example. But what do organisms like the little rotifer do? Adineta ricciae, that has evidently only reproduced asexually for millions of years? Have you possibly found other ways to create genetic variability?

Scientists from the Universities of Cambridge and Angers and the Max Planck Institute for Molecular Plant Physiology in Potsdam have investigated the adaptability of this microscopic multicellular organism with regard to dehydration. The basis of their considerations was the so-called Meselson effect. It says that in the course of asexual reproduction, alleles (these are variants of the same gene) develop independently of one another, since their genetic sequences are no longer checked for similarity when the sex cells are formed (meiosis). In this way, an asexually reproducing organism would also have genetic variability. Would it be possible to find evidence of this particular evolutionary mechanism in a particular gene?

The scientists selected a pair of alleles, i.e. the two variants of a gene whose proteins are related to the rotifer's tolerance to dehydration: one protein prevents the proteins in the cell from clumping together when the cells become dehydrated, the other protein protects the cell membrane from damage Dehydration by binding to them and preventing them from tearing. This changed binding property of the protein is due to a sequence change in the associated gene. In fact, the two gene variants differ in 13.5 percent of their sequence. That is a comparatively high value: "Such a sequence difference within two alleles is not achieved in sexually reproducing organisms," says Max Planck scientist Dirk Hincha. The work of the researchers thus provides evidence that the effect postulated by Meselson actually occurs in nature and represents an effective adaptation mechanism for an asexually reproducing organism. Presumably can Adineta Ricciae therefore have not had sex for millions of years.

Christina Beck (2007)