On elytral morphology, sexual conflict and female mating polymorphism in diving beetles: new paper in "Interface"

Posted by Erik Svensson

Forrmer PhD-student Kristina Karlsson-Green (currently postdoc in the "Metapopulation Research Group in Helsinkki, Finland) has published one of her last thesis-paper in the Royal Society Journal "Interface". This paper deals with a fascinating female mating polymorphism in diving beetles, where females have either a "rough" or "smooth" elytral morphology. She has quantified fine-scale female elytral morphology using scanning electron microscopy (SEM), as well as male morphological adaptations to clasp females during matings in the form of so-called "suction cups" (see picture above), and also used a biomechanical experiments to quantify male adhesion ability on the different female morphologies.

Results provide experimental support to the suggestion that this female mating polymorphism is maintained by sexually antagonistic and frequency-dependent selection caused by sexual conflict, and different male phenotypes show different ability to clasp the different female morphs. The experiments in this fascinating study were performed in collaboration with our colleague Prof. Stanislav N. Gorb, at Kiel University (Germany), and I personally like this combination of biomechanics and evolutionary biology very much. Below, you find a link and Abstract to the study.

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

1. Kristina Karlsson Green, 
2. Alexander Kovalev, 
3. Erik I. Svensson and
4. Stanislav N. Gorb

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.