Male animals are under greater selection pressures than females, which may allow populations to adapt more effectively to environmental changes, according to a report published in the open-access journal eLife.
The study supports one of the long-held assumptions behind the idea that sexual selection enhances adaptation: that stronger selection on males allows them to purge the population of genetic mutations that reduce ability. survival.
Sexual selection is selection resulting from competition for mating partners and / or their reproductive cells (their eggs or sperm). For nearly a century, researchers have believed that sexual selection is the ultimate selective force that generates the differences we see between male and female animals in terms of reproductive capacity and life history. Yet, little is known about how sexual selection combines with other environmental pressures to impact the demographics and adaptive capacity of the population.
Living organisms accumulate mutations throughout their lives – some of which help them become more able to survive, and others provide no benefit and may even cause harm (called deleterious mutations). Sexual selection is believed to promote evolutionary adaptation if it results in stronger net selection – that is, total purifying selection against deleterious mutations – in males rather than females. Indeed, the productivity of a population depends on the ability of females to reproduce, so that a stronger net selection on males allows a population to quickly get rid of deleterious mutations and to adapt to its environment. at lower cost to the population, which may eventually reduce the risk of extinction.
“Our knowledge of whether stronger sexual selection in males translates into stronger net selection in females is still limited,” says lead author Lennart Winkler, doctoral student at TU Dresden, Germany. “Previous studies have used the phenotypic variance of fitness to measure net selection, but its relevance has been questioned. An alternative measure is the genetic variance of the body’s fitness. We have used both measures for to show whether net selection is generally stronger in males across a wide range of species. “
The team performed a systematic literature search and compiled 101 matched estimates of male and female genetic variances across 26 species for two important components of an organism’s fitness: reproductive success and lifespan.
They then tested whether the phenotypic variances aligned with the genetic variances and whether the genetic variances exhibited consistent sex differences. They predicted that males would show greater genetic variance in reproductive success but not in lifespan.
They found that the phenotypic variance in lifespan but not in reproductive success predicted genetic variance in males or females. Importantly, however, the phenotypic variance in reproductive success was greater in males than in females, resulting in male bias in genetic variance. This difference between the sexes could be detected in polygamous but not monogamous species. In contrast, there were no consistent sex differences in phenotypic or genetic variance over lifespan.
“Our results have two major implications,” says lead author Tim Janicke, researcher at the Center for Functional and Evolutionary Ecology in Montpellier, France. “First, the phenotypic variance of reproductive success is a poor predictor of purifying selection against deleterious mutations. Second, our results support the prediction that net selection is generally stronger in males than in females, which may not only enhance local adaptation, but may also reduce the risk of extinction when populations are faced with difficult environmental conditions. Therefore, our results support the idea that sexual selection may play a central role in evolutionary rescue. “
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