Linking intra- and interspecific assortative mating: Consequences for asymmetric sexual isolation

Abstract

Assortative mating is of interest because of its role in speciation and the maintenance of species boundaries. However, we know little about how within-species assortment is related to interspecific sexual isolation. Most previous studies of assortative mating have focused on a single trait in males and females, rather than utilizing multivariate trait information. Here, we investigate how intraspecific assortative mating relates to sexual isolation in two sympatric and congeneric damselfly species (genus Calopteryx). We connect intraspecific assortment to interspecific sexual isolation by combining field observations, mate preference experiments, and enforced copulation experiments. Using canonical correlation analysis, we demonstrate multivariate intraspecific assortment for body size and body shape. Males of the smaller species mate more frequently with heterospecific females than males of the larger species, which showed less attraction to small heterospecific females. Field experiments suggest that sexual isolation asymmetry is caused by male preferences for large heterospecific females, rather than by mechanical isolation due to interspecific size differences or female preferences for large males. Male preferences for large females and male-male competition for high quality females can therefore counteract sexual isolation. This sexual isolation asymmetry indicates that sexual selection currently opposes a species boundary.

Sexual conflict and ecology: Species composition and male density interact to reduce male mating harassment and increase female survival

“…Also, our previous experimental work has shown that C. virgo males discriminate strongly against C. splendens females (Svensson et al. , ), suggesting that such heterospecific males should not affect C. splendens female survival directly, but only possibly indirectly through these heterospecific males interactions with C. splendens males, which we aimed to investigate in this study. Based on these features of the natural history and ecology of these damselfly species, we therefore feel confident in our assumption that conspecific male density and species composition are the two most important factors that are likely to affect C. splendens female survival, with little or no effect of female–female interactions or heterospecific male–female interactions.…”

“…, , Svensson et al. , , , , ) strongly suggest that interspecific interactions can modify the outcome of sexual conflict through interspecific reproductive interference between males. Our results call for the incorporation of more ecological realism in the study of sexual conflict, particularly how local community composition interspecific interactions could have different fitness consequences for the two sexes.…”

“…During clasping, males and females form the tandem position, after which females must bend their abdomen to reach male genitalia, forming the mating wheel (Corbet ; Svensson et al. ). After mating, females move to submerged vegetation along the river where they oviposit.…”

“…These courtship differences between the two species make heterospecific mating attempts rare and highly asymmetric, with C. splendens males more often mating with C. virgo females than vice versa (Svensson et al. , ).…”

“…Geographic locations and other ecological information about these sites are provided in detail elsewhere (Svensson et al. , , , ). One hundred sixty‐eight individuals were captured and used in our experiments in this study, 60 of which were females (48 C. splendens and 12 C. virgo ) and 108 of which were males (72 C. splendens and 36 C. virgo ).…”