Males of a species evolving traits for sexual conflict could cause problems for females, and, ultimately, the entire population.
A latest model by Imperial College London and University of Lausanne researchers, published in Proceedings of the National Academy of Sciences, shows how so-called ‘good genes’ can sometimes cause a population to collapse.
Males of any species may compete for females, either by fighting other males for access or impressing females to win their approval. In each cases, males expressing probably the most competitive traits – reminiscent of the perfect ornaments, like peacock feathers, or the perfect weapons, like big body size – access more females.
To have the perfect traits the males have to be in good condition, for instance to be in higher shape or carry less disease. Over time, as better-condition males mate with more females, the prevalence of ‘good genes’ increases throughout the population of the animal, resulting in the population as an entire to enhance in condition.
Nonetheless, it might probably also backfire. Traits than improve a male’s competitive prowess also can damage females. For instance, some insect males have evolved penises that tear the females’ insides, and in lots of species, including mammals, males have evolved to harass females to induce mating. These behaviors reduce female fecundity or may even kill them.
The team’s model tested theories of sexual competition where males harm females, and compared the outcomes with data for various population experiments. Previous experiments have shown conflicting accounts as as to whether sexual selection is positive or negative for the population as an entire. The brand new model provides a proof for why some experiments show male condition improving, without female fitness or population viability improving alongside.
Where males evolve selfish traits that help them individually win, they’ll actually find yourself causing the population to crash – it is a type of evolutionary suicide. Even when females evolve to counter male harm and forestall population collapse, the population still decreases significantly, reducing its viability.”
Dr Ewan Flintham, First Writer, Imperial College London and the University of Lausanne
Sexual interactions like these are a very important component of understanding population demographics and conservation. For instance, where there are more males, sexual competition intensifies, meaning harm towards females is more likely. This can also be true in human-managed populations, for instance domestic carp, where women and men have to be isolated during spawning season.
Dr Flintham accomplished the research as a part of the Centre for Doctoral Training in Quantitative and Modelling Skills in Ecology and Evolution at Imperial. His project supervisor and study co-author Professor Vincent Savolainen, Director of the Georgina Mace Centre for the Living Planet at Imperial, said: “Male harm evolved in nature as something that was presupposed to be good, but is detrimental to females and the entire population. Questions like how and why this happens can only be answered with quantitative methods – data and mathematical models – which might be just as necessary as field studies.”
Source:
Journal reference:
Flintham, E.O., et al. (2023) Male harm offsets the demographic advantages of fine genes. PNAS. doi.org/10.1073/pnas.2211668120.