Few males can fertilize all the females. A population's growth is not affected by the number of males. They are however important in removing bad mutations from the population. A new Uppsala University study reveals this. It provides detailed knowledge about the long-term genetic consequences that sexual selection may have. These results were published in Evolution Letters, a scientific journal.This study supports the idea that selection on males in animal species can have the unintended benefit of creating healthy offspring. In order to prevent them from passing on certain mutations, males with many deleterious mutations must compete for the females. This could have positive long-term consequences for a sexually reproducing population's growth, persistence, and longevity.The process of removing deleterious mutations from a population by rigorous selection in males can have little to no effect on the population's growth. Because there are only a few males who can fertilize all of the females in a population. This means that it doesn't make a difference how many offspring the females can produce. Karl Grieshop, an evolutionary biologist at Canada’s University of Toronto, and the study's principal author, says that such strict selection of females would lead to fewer females reproducing and therefore fewer offspring being produced. This could cause a huge population decline or even extinction.Researchers used 16 genetic strains from Callosobruchus maculatus seed beetle to study how the inferred number and severity of deleterious mutations affected both the reproductive abilities (or fitness) of males and females. It was possible to quantify each strain's unique mutations by inbreeding and crossing them. Scientists were able to compare the effects of these mutations on males and females by comparing them to crosses. These mutational effects only occurred in male fitness when we only looked at crosses between strains. This is because the genetically more variable setting is more relevant to how natural selection will act in nature. The negative effects of mutations in females were not evident in this genetically more variable background. Therefore, female-specific selection would not work effectively to eliminate them.This indicates that, although these mutations can have a negative effect on female reproduction, they are easier to eradicate by selection on male carriers rather than female carriers. Grieshop states that although previous research by Grieshop and others has shown this effect, this is the first time it has been demonstrated for naturally occurring variants.According to the researchers, the study sheds new light upon the question of why multicellular organisms can use sexual reproduction."Production males results in a decrease of the species' reproductive capacity, as males contribute less to the generation of offspring than the females. It is important to understand why a species chooses to reproduce sexually rather than merely producing females by asexual reproduction. Our study shows that males may compete for the chance of mate and this could lead to faster removal of harmful mutations. This could allow for a better set of genes and a higher reproductive ability relative to asexual reproduction," said David Berger, researcher and leader of the Uppsala University Department of Ecology and Genetics.###Grieshop, K. and others. (2021), Selection of males purges mutations on female fitness, Evolution letters. DOI: 10.1002/evl3.239.
