The effect of differing levels of intrasexual and intersexual selection on survival and reproduction under a heatwave

Heatwaves are set to become more common due to climate change, and the potential of heatwaves to damage a species' populations is becoming more apparent. One way heatwaves can affect reproduction is by changing the dynamics of precopulatory mating behaviours, which can detrimentally impact individuals' survival and reproductive success. However, little work has been done to investigate how different levels of intrasexual and intersexual selection in precopulatory behaviours, such as male–male competition or female-mate choice, modulate fitness responses to heatwave. Here we investigate how differing levels of male competition and female choice impact survival and reproductive success when a heatwave event occurs, using cool-adapted Scottish populations of the burying beetle Nicrophorus vespilloides as a model system. We implemented three treatments for precopulatory conditions: monogamy (one male, one female, no male–male competition), polyandry with male competition (one female, two males, where males and females could freely interact), and polyandry with low male competition (one female, two males, where males could not interact with each other or the female freely). We then subjected the beetles to a heatwave event (3 days at 25°C) at the time of mating. We found that reproductive fitness decreased under a heatwave in the polyandry/low male competition treatment, compared to both the monogamy and the male competition treatments. Our results indicate that differing levels of intrasexual and intersexual selection can moderate the detrimental effects of heatwaves in wild species.