Males are responsible for the genetic fitness of a population

Sexual competition among males important for maintaining genetically healthy populations. A new study from Uppsala University describes how sexual selection eliminates bad mutations, and helps to pass along genes to offspring that tend to increase their fitness.

“When deleterious mutations are purged from a population through rigorous selection in males, resulting in fewer males reproducing, the process can take place with little or no effect on population growth.”

“This is because relatively few males suffice to fertilize all the females in a population, hence, whether those females are fertilized by few males or many males makes little or no difference to the number of offspring those females can produce, especially in species where the male doesn’t look after its own offspring,” explained study lead author Karl Grieshop, an evolutionary biologist at the University of Toronto.

“By contrast, such rigorous selection in females would result in fewer females reproducing, hence fewer offspring produced, which could lead to a massive population decline or even extinction.’

The researchers analyzed 16 genetic strains of seed beetle to investigate how the number of deleterious mutations in each affected their reproductive ability. 

The experts quantified the cumulative effects of each strain’s unique set of mutations through the intensive inbreeding of strains followed by crosses among them. This showed that the mutations harmed both females and males nearly equally. 

However, when the team looked at just the crosses among strains, which is the more more how selection would act in nature, the mutational effects only impacted male fitness. In the females, the deleterious effects of the mutations they carried were not detectable in this more genetically variable background.

“This indicates that although these mutations do have a detrimental effect on females’ reproduction, they are more effectively removed from the population by selection acting on male carriers than female carriers,” said Grieshop.

“Previous research from our group and others has succeeded in showing this effect by artificially inducing mutations, but this is the first direct evidence that it ensues for naturally occurring variants of genes.”

According to the researchers, their study sheds new light on the old question of why so many multicellular organisms use sexual reproduction.

“Production of males causes a decrease in the reproductive capacity of a species, since males themselves contribute less than females to the production of offspring. The question, then, is why a species evolves to reproduce sexually, instead of just producing females through asexual reproduction,” said study co-author David Berger.

“Our study shows that production of males, which may engage in intense competition for the chance to mate, enables faster purging of deleterious mutations from the population, which could thereby enable a healthier set of genes and higher reproductive capacity relative to asexual reproduction.”

The study is published in the journal Evolution Letters.

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By Chrissy Sexton, Earth.com Staff Writer