Male clasping ability, female polymorphism and sexual conflict: fine-scale elytral morphology as a sexually antagonistic adaptation in female diving beetles

Abstract

During sexual conflict, males and females are expected to evolve traits and behaviours with a sexually antagonistic function. Recently, sexually antagonistic coevolution was proposed to occur between male and female diving beetles (Dytiscidae). Male diving beetles possess numerous suction cups on their forelegs whereas females commonly have rough structures on their elytra. These rough structures have been suggested to obstruct adhesion from male suction cups during mating attempts. However, some diving beetle species are dimorphic, where one female morph has a rough elytra and the other has a smooth elytra. Here, we used biomechanics to study the adhesive performance of male suction cups on the female morphs in two diving beetle species: Dytiscus lapponicus and Graphoderus zonatus. We compared adhesion on the rough and the smooth female morphs to infer the function of the rough elytral modifications. We found that the adhesive force on the rough structures was much lower than on other surfaces. These findings support the suggestion of sexual conflict in diving beetles and a sexually antagonistic function of the rough female structures. In addition, males differed in their adhesive capacity on different female surfaces, indicating a male trade-off between adhering to smooth and rough female morphs.

Back to basics: using colour polymorphisms to study evolutionary processes

“…We have also studied other forms of heritable polymorphisms, such as elythral polymorphisms in female diving beetles, which is a female adaptation against male mating harassment (Karlsson et al . , ). In our research on female‐limited colour polymorphisms in the damselfly Ischnura elegans , we have investigated how the different female morphs cope with frequency‐dependent male mating harassment in both natural populations and in mesocosm experiments (Svensson et al .…”

Adhesion tilt-tolerance in bio-inspired mushroom-shaped adhesive microstructure

“…These setae as well as setae of other beetles 3 and earwigs 24 also contain an additional jointlike structure at the base of pillars. Such basal joints together with joints under the terminal contact elements are also known for suction cups of males of aquatic beetles 25 [Figs. 6(c) and 6(d)].…”

Resolving the taxonomic conundrum in Graphoderus of the east Palearctic with a key to all species (Coleoptera, Dytiscidae)

“…Another Graphoderus species which has received substantial attention lately is Graphoderus zonatus and in particular its subspecies Graphoderus zonatus verrucifer , as its females are dimorphic with one morph dorsally smooth like the male and the other morph with a peculiar wrinkly pronotum and roughly granulated elytra (Nilsson 1986, Nilsson and Holmen 1995, Bergsten et al 2001, Härdling and Bergsten 2006, Karlsson-Green et al 2013, 2014). The two morphs co-occur in varying proportions in different populations and it was shown by Bergsten et al (2001) that the proportion of the granulate morphs in a population was significantly correlated with suction cup characteristics of the male’s pro- and mesotarsal palettes.…”

“…frequency and timing (Arnqvist and Rowe 2005). The antagonistic nature of the dorsal female sculpture to the function of the mechanically working male suction cups was inferred mathematically from first principles by Bergsten and Miller (2007) and later shown empirically (Karlsson-Green et al 2013). Both theoretical (Härdling and Bergsten 2006) and empirical (Karlsson-Green et al 2014) work has been conducted to try to understand the role of selection and drift for the distinct morphs to be able to co-occur over time.…”