“Intralocus sexual conflict and the tragedy of the commons in seed beetles”

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David Berger, Ivain Martinossi, Karl Grieshop, Martin I. Lind, Alexei A. Maklakov, and Göran Arnqvist

Intralocus sexual conflict causes a tragedy of the commons in seed beetles

How the battle of the sexes can mean the demise of populations

A pair of Callosobruchus maculatus seed beetles mating. The male (to the left) has inserted his spiky genitalia into the reproductive tract of the female (to the right). The male is leaning backwards, a sign of successful copulation.
(Credit: Lena Brinkert)

Researchers from the Department of Ecology and Genetics at Uppsala University have shown that two forms of conflict between males and females can simultaneously increase extinction risk in sexually reproducing species. Males compete over access to females and evolve adaptations that increase their chances in the mating game. In many animals, such adaptations include changes in male behavior or the anatomy of genitalia that inflict harm on females during mating, thereby spurring a conflict between the sexes. These adaptations, while beneficial to individual males, can be detrimental to the population as a whole by lowering the number of offspring produced by females. The researchers predicted that this effect should be magnified whenever the genes underlying such selfish male strategies also have direct negative effects on condition and health when expressed in females. This other form of sexual conflict occurs at the gene level and has received much investigation, but tests of its consequences at the population level were lacking.

The researchers tested the hypothesis by measuring different characteristics and the reproductive performances of males and females from different genetic strains of seed beetle. They then created artificial populations from each strain to measure how the interaction between the sexes within each strain affected population viability. The strains that carried gene variants associated with a “live fast–die young” lifestyle, associated with high male mating success but low female offspring production, had the lowest observed population viabilities. Thus, these male-beneficial genes likely reduce population viability both by increasing male-inflicted harm on females during mating, and by having detrimental health effects when expressed in females. The published study demonstrates how sexual conflict fueled by selection at the gene level can have severe consequences at the population level.