Researchers at the University of St Andrews have discovered that heat stress alters the mating behavior of Nicrophorus vespilloides, or burying beetles, causing males to mount other males more frequently. While scientists previously suspected this was a sex recognition error,
new observations indicate that same-sex mounting is common even under normal conditions.
Heat Stress and Chemical Communication in Burying Beetles
The burying beetle, known for its unique parental care—which involves burying small carcasses to create a nursery for its offspring—relies heavily on chemical signals to navigate its environment. These insects are coated in waxy molecules called cuticular hydrocarbons (CHCs), which serve two primary functions: preventing dehydration and facilitating social communication.
Solène Morelle, a PhD student at the University of St Andrews, is investigating how a warming climate impacts these beetles. Evidence suggests that there is a trade-off between the signalling and waterproofing functions of CHCs,
Morelle explained. In hotter, drier environments, beetles likely prioritize longer-chain CHCs to prevent water loss, as these are less prone to evaporation. However, these longer-chain molecules are less effective as signals compared to the more volatile shorter-chain CHCs, potentially leaving beetles unable to accurately identify the sex or status of their counterparts.
Experimental Findings on Same-Sex Mounting
To test the impact of rising temperatures on behavior, researchers compared beetles kept at a baseline of 68 degrees Fahrenheit with a group exposed to a simulated three-day heatwave at 79 degrees Fahrenheit. The team presented their findings, which involved analyzing the beetles’ chemical profiles via gas chromatography-mass spectrometry, at the Society for Experimental Biology conference in Florence, Italy.
“I was surprised to find out how much same-sex mounting the beetles showed, even under normal conditions.”
Solène Morelle, University of St Andrews
While the study confirmed that male beetles mount other males more often during heat stress, the prevalence of this behavior at normal temperatures was unexpected. The researchers noted that reciprocal mounting under heat stress
increased, but they do not yet have a definitive explanation for why this occurs.
The Evolutionary Cost of Reproductive Mistakes
One core question is whether these mounting encounters are detrimental to the species. Because burying beetles operate in a competitive environment where rivals may seize a carcass and kill existing larvae, effective communication is vital for long-term reproductive success. If heat disrupts the olfactory pathways that allow beetles to distinguish between a cooperative partner and a competitor, the consequences could extend well beyond a wasted mating attempt.
However, the immediate cost of a failed mating attempt may be lower than the risk of missing a legitimate opportunity. According to Morelle, the physiological cost of a single unsuccessful mating attempt probably isn’t very high on its own and does not outweigh the risk of losing a chance to mate with a female.
Mounting may also serve purposes unrelated to reproduction, such as responding to competition, social conflict or periods of high activity, meaning the behavior may be part of a broader, more complex social pattern rather than a simple failure of recognition.
Future Implications for Beetle Populations
The research underscores the vulnerability of ectothermic insects to climate-driven environmental shifts. Because these beetles cannot regulate their own body temperature, they are particularly susceptible to the physiological changes induced by a warming planet. As heat-induced changes in CHC profiles may alter behavioural and reproductive outcomes,
the researchers are continuing to examine whether these communication disruptions will lead to long-term population declines.
The team is currently working to understand the full scope of these behavioral shifts. For now, the increased rate of same-sex mounting serves as a indicator of how sensitive these insects are to even moderate increases in ambient temperature.