Male ‘good genes’ may be causing harm in some species

Within mammals, birds, insects and other classes of animals, there are species in which, in their sexual rituals, the males fight hand to hand to show which of them is stronger. The consequence of this dispute is that they win the right to mate with the females

As a consequence of these confrontations, the species guarantee the reproduction of “good genes”, those that the dominant male carries, and that would make his offspring retain their size, strength, and resistance to diseases, among other genotypic qualities.

However, the species in which these behaviours occur could be affected in the long term, according to the findings of a study recently published in the Journal of the National Academy of Sciences.

According to the research, the males, in addition to causing damage to each other, can cause damage to the female during mating, compromising her fertility capacity in the long term. Some examples of these behaviours are found in insects and mammals, whose males may strike females or cause damage to them with their penis during mating.

According to the mathematical models proposed in the study, this could be causing females to evolve more slowly than males. This has consequences on the life dynamics of the species and can even reduce the size of the populations in the long term.

Evolutionary suicide

The authors affirm that this model confronts two crucial elements for the species: the benefits that sexual selection has in the reproduction of dominant genes, as opposed to the consequences that sexual conflicts can have in the individuals of the species. 

In conclusion, they ensure that in some species the balance is tipped in the long term by negative consequences since the reproduction of dominant genes leads to increasingly strong conflicts, as well as the damage caused to females.

First author Dr Ewan Flintham, from Imperial College London and the University of Lausanne, said: “When males develop selfish traits that help them win individually, they can actually end up causing population collapse, it’s a way of evolutionary suicide”. Even when females evolve to counteract damage from males and prevent population collapse, the population continues to decline significantly, reducing their viability.”

Sexual interactions like these are an important component of understanding population demography and conservation. For example, where there are more males, sexual competition intensifies, meaning that females are more likely to be harmed. This is also true of human-managed populations, for example, domestic carp, where males and females must be isolated during the spawning season.

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