Mate choice by non-virgin females contributes to reproductive isolation between populations of the Harlequin beetle-riding pseudoscorpion

Abstract

Determining whether reproductive isolation evolves through mate choice and . or gametic factors that prevent fertilization or through the post-zygotic mechanisms of hybrid sterility or inviability is undamental to understanding speciation. Investigation of the pre- and post-zygotic components of reproductive isolation is facilitated in the pseudoscorpion, Cordylochernes scorpioides, by its indirect method of sperm transfer and viviparous embryonic development. Previous research on this species, in which mate discrimination was assessed in virgin females, suggested that female choice played only a minor role in reproductive isolation between populations from French Guiana and Panama_L . Here, in a study of three allopatric populations of C. scorpioides from Panama_L , we assessed mating-stage isolation in both virgin and once-mated females, and found that female discrimination depends critically on mating status. Virgin females were almost invariably receptive, showing no tendency to discriminate against males from allopatric populations. By contrast, non-virgin females were significantly more likely to reject foreign males than males from their own population. Male sexual motivation could not account for differences in either female sexual receptivity or male success in sperm transfer. Allopatric and sympatric males did not differ in number of spermatophores deposited as either a female_fs first or second mate. Nonetheless, allopatric males achieved significantly lower sperm transfer success not only with choosy, non-virgin females but also with virgin females. Given the lack of behavioral discrimination by virgin females, female receptivity was not the only factor influencing differences in sperm transfer success. Multivariate analysis of spermatophore morphology suggests that the higher failure rate of ratings between allopatric males and virgin females resulted from population differences in sperm packet architecture. Overall, our findings indicate that assessment of discrimination against allopatric males that is limited to virgin females may seriously underestimate the contribution of female mate choice to reproductive isolation between populations.