Having More Sex Makes These Male Beetles Feel Insecure

In human culture, we normally correlate sexual success with better self esteem. A male that attracts more females is more likely to feel secure in his social standing, so the reasoning might go. But according to a recent study published in Evolution, the opposite is true—at least when applied to beetles.

The study's authors, based out of the University of Exeter, wanted to investigate the behavioral plasticity of the Nicrophorus vespilloidesbeetle relative to its breeding success. The goal was to determine whether the more sexually successful males adapted to their dominant social roles by behaving differently than their less promiscuous brethren.

To get to the bottom of this question, the Exeter team artificially separated male beetles into two testing groups: one group that mated at high rates, and the other that mated at low rates. The researchers found that the beetles that mated more became much more sensitive to the sizes and social ranking of competitor beetles than those that mated less.

"What is really fascinating is that this social sensitivity has evolved in response to selection on mating behaviour: males that have more sex really are more insecure about their social status," said behavioral ecologist Nick Royle, a co-author on the study, in a statement. "Our results therefore provide valuable insights as to how behavioural plasticity evolves."

The more promiscuous males manifested their insecurity by challenging rivals of lesser size more aggressively. When faced with larger rivals, conversely, high rate males were more likely to behave deferentially than low rate males. The results seem to suggest that the males adjust their behavior when they have more evolutionary resources to lose.

This makes sense given the behavior of these insects in the wild. Burying beetles start to feel frisky once they've located decaying rodent carcasses, which they eventually repurpose into nests for their young. Usually, both males and females will duke it out with their respective competitors until a dominant couple, or team of couples, is left to take over these morbid corpse-nurseries.

Size is the main factor that determines which beetles claim the carrion turf, but the losers still have opportunities to mate, if they are smart about it. For example, rejected females will lay eggs close to those of dominant females, hoping they will be fertilized thanks to sheer proximity. Similarly, rejected males can occasionally score a quick, sneaky copulation with females without directly confronting the dominant males. This strategy known as the "satellite tactic," and it's commonly used by males across many species.

Given that the dominant males are more likely to be sneakily cuckolded in this way, their social sensitivity to competitors makes sense. But to delve into the deeper mechanics behind this behavioral shift, researchers will have to study it with a wider range of methods as well as across a wider range of species.

"Such flexibility of behaviour in response to a change in social context is a common, but relatively poorly understood, feature of organisms," said co-author and evolutionary biologist Mauricio Carter said in a statement.

"Plasticity of behaviour is important because it allows organisms to respond rapidly to changes, increasing the persistence of populations in the face of environmental fluctuations," he continued. "Our research increases our understanding of this important process that helps organisms adapt to changes in their environment."

Sure, it's good to be at the top, and more sexually successful beetles will reap the benefits that goes along with their insecurity down the evolutionary line. But there's a condolence prize for the less promiscuous males too: they don't have to deal with all the posturing and doubt associated with being king of a gross rodent carcass.