In many animal species, including human species, only a handful of males can be sufficient to pollinate all females and thus ensure generational renewal. Why are they born with this number at the expense of females?

Researchers from Uppsala University (Sweden) have provided a new answer. In a study published in the scientific journal evolution messages رسائل, they demonstrate that the presence of a large number of males makes it possible to eliminate bad genetic mutations from the population. Which, in the long run, has genetic consequences for sexual selection.

Mutations are present but undetectable in females

To conduct their work, the researchers relied on the theory that in many animal species, fierce competition between males to fertilize females selectively eliminates individuals with many harmful mutations, preventing them from transmitting these mutations. This selection has long-term positive effects on the growth and persistence of sexually reproducing populations.

They then verified this using 16 genetic strains of the seed beetle (Callosobruchus maculatus). Their goal was to study how the putative number of harmful mutations in each affects the reproductive capacity (fitness) of females and males. The scientists tracked the strains with high inbreeding, which allowed them to determine the cumulative effects of a unique set of mutations for each strain. By comparing inbred strains and crosses between them, they were able to see that these mutations harm females and males roughly equally. However, the effects of mutations It manifests itself only in the physical condition of the male. In females, the deleterious effects of the mutations they carry have not been detectable in this more genetically diverse context. So it will not be effectively eliminated by female-specific selection in the wild.

“This suggests that although these mutations have a detrimental effect on female reproduction, they are more effectively removed from the population by selection that acts on male carriers than on female carriers.”, points to Carl Grishop, an evolutionary biologist at the Canadian University of Toronto and lead author of the study.

Rapid elimination of harmful genes by males

According to the study authors, this new work sheds new light on the age-old question of why many multicellular organisms resort to sexual reproduction.

“Male production results in a decrease in the reproductive capacity of the species, because males themselves contribute less than females to the production of offspring. The question is therefore why species evolve to reproduce sexually., rather than to produce only females. by asexual reproduction. Our study shows that male production , who can compete fiercely for the opportunity to mate, allows harmful mutations to be removed in the population faster, which may provide a healthier set of genes and higher reproductive capacity compared to asexual reproduction.concludes David Berger, researcher and team leader in the Department of Ecology and Genetics at Uppsala University.