A General Explanation for the Persistence of Reproductive Interference

Abstract

Reproductive interference is widespread, despite the theoretical expectation that it should be eliminated by reproductive character displacement (RCD). A possible explanation is that females of sympatric species are too similar phenotypically for males to distinguish between them, resulting in a type of evolutionary dilemma or catch-22 in which reproductive interference persists because male mate recognition (MR) cannot evolve until female phenotypes diverge further, and vice versa. Here we illustrate and test this hypothesis with data on rubyspot damselflies (Hetaerina spp.). First, reproductive isolation owing to male MR breaks down with increasing interspecific similarity in female phenotypes. Second, comparing allopatric and sympatric populations yielded no evidence for RCD, suggesting that parallel divergence in female coloration and male MR in allopatry determines the level of reproductive isolation on secondary contact. Whenever reproductive isolation depends on male MR and females of sympatric species are phenotypically similar, the evolutionary catch-22 hypothesis offers an explanation for the persistence of reproductive interference.

Predicting evolutionary responses to interspecific interference in the wild

“…Why some sympatric populations with low reproductive divergence have not diverged from each other remains to be determined. Possible reasons include evolutionary time lag (if secondary contact occurred recently) and gene flow from allopatry swamping selection in sympatry, although most Hetaerina populations are strongly differentiated genetically (see Appendix of Drury et al ).…”

“…We therefore used a Monte Carlo simulation to estimate what the reduction in a male’s mating success would be if heterospecific males shared territories. We assumed that clasping probabilities in sympatry can be used to simulate conditions at the time of secondary contact, because clasping probabilities do not differ between population in sympatry and allopatry, and most Hetaerina populations are strongly differentiated genetically (Drury et al ). Nevertheless, clasping probabilities alone are insufficient for estimating d .…”

“…If female pre‐clasping mate recognition were evolvable (with females controlling whether they are clasped), then all populations would evolve towards zero reproductive interference and zero interspecific aggression (Okamoto & Grether ). Male mate recognition was also assumed not to evolve, based on evidence that reproductive interference does not affect the evolution of male mate recognition in Hetaerina (Drury et al ).…”

“…This was repeated 10 4 times, and the resulting mean r s was compared to Spearman correlation critical values for N = 16. Patristic distances were obtained from the phylogeny of Drury et al ().…”

“…Although interspecies pairs break up prior to copulation, males can clasp and fly in tandem with heterospecific females, potentially resulting in interspecific mate competition within male territories (Drury et al ). The ability of males to distinguish between conspecific and heterospecific females varies considerably among species pairs (Drury et al ) but is not enhanced in sympatry compared to allopatry (Drury et al ). Thus, current levels of reproductive interference are probably representative of the levels that occurred at the time of secondary contact.…”