Variation in both male and female secondary sexual characters in the diving beetle, Agabus bipustulatus (L.) (Coleoptera: Dytiscidae)

William Howe


Sexual conflict and intersexual arms races occur due to the differing evolutionary interests between the sexes. Under the model of sexual conflict it is predicted that this will lead to sexual dimorphism, common in diving beetles, where males have suckers which they use to attach to the females’ dorsal surface to potentially increase their copulatory ability. These are often met by female counteradaptations in an attempt to avoid multiple and potentially costly matings. This can result in a cyclical battle of responses in both sexes. Within the widely distributed species, Agabus bipustulatus there is known variation in female sculpture from intensely matt individuals that are highly reticulated to smooth, shiny individuals where reticulation is highly obsolete. We investigate this quantitatively across three populations that differ in reticulation and we also quantitatively investigate whether there are differences in male attachment devices. We show that reticulation of females varies markedly across the three populations of A.bipustulatus and suggest that the degree of reticulation in females may correspond to variation in male attachment devices. We suggest that in populations of highly reticulated females more small and large suckers are selected for in males to presumably aid their ability to coerce the female to mate.

Keywords: Agabus - Sexual conflict - evolutionary arms race – dimorphism- counteradaptation - reticulation.

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