Sexual conflict affects females more than males, says new research on beetles

These beetles have surprisingly complex parental care, similar in form to that provided by birds such as robins or blackbirds, with offspring begging to be fed by touching parents, who respond by regurgitating partially digested food.

Both males and females provide parental care, but females are the primary care givers, as in humans. So anything that affects the ability of females to provide parental care, such as costly mating, is likely to reduce overall reproductive productivity.

New work published today in the journal Ecology Letters, used artificial selection and mating crosses among selection lines to determine if and how mating behaviors co-evolve with parental care behaviors.

Classical parental care theory suggests that males are expected to provide less care when offspring in a brood are less likely to be their own. However, previous research indicates that this is not always the case, and one reason for this could be because costs associated with behaviors during mating impact behaviors during parental care.

The study tested this idea by artificially selecting burying beetles for either high or low mating rate (a paternity assurance trait) for 7 generations. Patterns of parental care and productivity of different combinations of male-female pairs from the same or different selection lines were then examined to see whether selection on mating behavior led to a correlated, co-evolutionary response in parental care behavior.

Male parental care behavior did not change in response to selection on mating rate, but females responded to selection for high mating rates with a reduction in parental care. Productivity of pairs with females from lines selected for high mating rate was lower than that for pairs where females were from lines selected for low mating rate due to costs of mating for females and because males did not compensate for changes in female behavior.

Dr Nick Royle, of the Centre for Ecology and Conservation at the University of Exeter, said: "Our research shows that, despite selecting on a mating behavior that is known to increase male assurance of paternity, there was no correlated change in male parental care behavior. Instead, costs of mating in females appear to determine how patterns of parental care evolve in response to changes in mating behavior. In species with biparental care, such as burying beetles, most birds and humans, our results indicate that males are followers not leaders in the evolution of family life. It is how selection acts on females, not males, that really counts here."

The results of the study are contrary to classical parental care theory and instead support the idea that sexual conflict is more important than parentage in determining patterns of parental care.