The influence of the relationship between male suckers and female hindlegs on mating in the diving beetle Eretes griseus

Sexual conflict occurs when males and females have conflicting interests over reproductive success, potentially leading to an evolutionary arms race. Many diving beetle species mate in water, with males using suckers to stick to females during mating. Prolonged mating by males with well-developed suckers can increase the risk of suffocation and predation for females. Several previous studies have reported that females of many diving beetle species possess rough dorsal surfaces, which may have evolved to reduce the stickiness of male suckers. However, in some species in which males possess suckers, there is no evidence of sexual dimorphism in dorsal surface morphology, leaving the nature of sexual conflict in diving beetles unclear. In the diving beetle Eretes griseus , the dorsal surface is not sexually dimorphic but males possess exaggerated suckers: two large suckers and many smaller suckers on the tarsus of each foreleg. Here, we observed the mating behaviour of E. griseus and analysed the relationship between male sucker traits and both mating success and female counteradaptations. We found that the number of small suckers was positively correlated with the number of matings and the duration of matings, but not the size of large suckers. Females had significantly longer hindlegs than males and frequently kicked males during mating. Our results suggest that in E. griseus , sexual conflict may have led to an arms race between the number of suckers in males and the length of hindlegs in females. • Male diving beetles use foreleg suckers to maintain contact during copulation. • This can increase the risk of suffocation and predation for females. • In many species, females counter this via rough dorsal surfaces. • Eretes griseus lack pronounced dorsal sexual dimorphism. • Females resist copulation by kicking males, which reduces copulation duration.