Exploring the Impacts of Sexual Conflict on Population Dynamics
Males of a species that develop sexually conflicting traits can create problems for females and eventually the entire population.
Here, a new model, prepared by researchers at Imperial College London and researchers at the University of Lausanne and published in the Proceedings of the National Academy of Sciences, shows how so-called “good genes” can sometimes cause population collapse.
Males of any species may compete for females, either by fighting off other males to gain access to females, or by persuading females and gaining their approval. In any case, the males that exhibit the most competitive traits, such as better ornaments (like peacock feathers) or better weapons (like large body size), turn to more females.
To have the best traits, males need to be in good shape, such as being less sick.
Over time, as wealthy males mate with more females, the “good genes” spread among the animals, resulting in improved overall health.
However, this can backfire. Traits that make males even more competitive can also harm females.
For example, some insectivores have evolved males to eviscerate females, and in many species, including mammals, males have evolved to harass females to encourage them to mate. This behavior reduces female fertility or can kill them.
The team’s model tested theories of sexual competition in which males harm females and compared the results with data from various population-based trials.
Previous experiments have shown conflicting data about whether sexual selection is positive or negative for the population as a whole. The new model offers an explanation for why some trials show that men improve rather than women in fitness or population survival along with improvements.
The first author, Dr Evan Flintham of Imperial College London and the University of Lausanne, said: “When males develop selfish traits that help them win individually, they can eventually cause population collapse. It’s a form of evolutionary suicide. Even when females evolve.” To counter male harm and prevent population collapse, the population continues to decline dramatically, reducing its viability.
Such sexual interactions are an important component of understanding and maintaining demographics. For example, where there are more males, sexual competition is fiercer, which means that harm to females is more likely. This also applies to human-managed populations, such as farmed carp, where males and females must be separated during the spawning season.
Dr. Flintham completed research within the Teaching Center for Doctoral Studies in Quantitative Skills and Modeling in Ecology and Evolution at Imperial College London.
Project leader and study co-author Professor Vincent Savolainen, director of the Georgina Mees Center for Living Planet Studies at Imperial College London, said: “Male harm has evolved in nature as something that should be beneficial but detrimental to health. females and the entire population. Questions such as how and why this happens cannot be answered. It is only through quantitative methods that data and mathematical models can be as important as field research.”
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