New research by biologists is shedding light on old questions about the role of males and why most multicellular organisms use sexual reproduction. According to the authors, males help maintain the genetic health of the population. The research results are published in the journal Evolution Letters.
To fertilize all females, only a few males are enough, therefore the number of males in a population has little effect on its total number. Moreover, it is theoretically possible to do without males altogether. However, most multicellular organisms prefer sexual reproduction and the number of males in them is approximately equal to the number of females. This fact serves as a reason for constant discussion among biologists about the role of males in the population.
Researchers from the Swedish University of Uppsala and the Canadian University of Toronto studied the possible long-term genetic consequences of sexual selection in beetles of the caryopsis family Callosobruchus maculatus and found that males are needed to clear the population of bad mutations.
"The production of males causes a decrease in the reproductive capacity of the species, since males contribute less than females to the production of offspring. Then the question arises why evolution chose the path of sexual reproduction, and not just asexual reproduction of females," study participants David Berger, Research Associate in the Department of Ecology and Genetics - Our research shows that producing males who can compete for mating more quickly clears harmful mutations in the population, thus ensuring a healthier set of genes and a higher reproductive capacity compared to asexual reproduction."
The results obtained support the existing theory that in many animal species, genetic selection and cleansing from the mutational load occurs mainly through the male line. Fierce competition between males leads to the selective elimination of individuals with genetic failures, preventing them from passing on harmful mutations by inheritance. This has a positive long-term effect on the growth and sustainability of the sexually reproducing population.
"When deleterious mutations are removed from a population through careful selection of males, it leads to a decrease in the number of males, but does not affect the size of the population as a whole, especially in species in which the male does not care for the offspring," says lead author of the study, an evolutionary biologist from University of Toronto Karl Grieshop - Such selection in females would lead to a decrease in the number of reproductive females, to fewer offspring, and, as a result, to a massive decline in the population or even to its extinction."
The researchers took 16 genetic lines, or strains of the beetle Callosobruchus maculatus, and tracked how the estimated number of deleterious mutations in each affected reproductive fitness. Separately, through intense inbreeding - closely related crossbreeding - the authors amplified the mutations and looked at how they are inherited within each strain.
It turned out that during inbreeding, both males and females inherited mutations, and when crossing between lines - in a situation more close to natural - mutational effects manifested themselves only in males.From this, the authors conclude that harmful mutations are indeed more efficiently removed from the population through their male carriers.