Genetic variation in a female genital trait evolved by sexual coevolution

Abstract

Understanding the patterns of genetic variation of traits subject to sexual selection is fundamental for explaining its evolutionary dynamics and potential for sexual coevolution. The signa of female Lepidoptera are sclerotized structures located on the inner surface of the genital receptacle that receives the spermatophore during copulation (the corpus bursae), whose main function is tearing the spermatophore envelope. Comparative data indicate that the evolution of signa has been influenced by sexually antagonistic coevolution with spermatophore envelopes. We looked for additive genetic variation in the size and shape of signa in females of the butterfly Callophrys xami (Lycaenidae) from two localities (BG and FC) in Mexico City. We also looked for genetic variation in female body size and in the size of corpus bursae. There were significant between-population differences in female body size, signa width and three signa shape traits. We found significant extranuclear maternal effects in one component of signa shape in the BG population, and in body weight, signa length and in one uniform component of signa shape in the FC population. Extranuclear maternal contributions could permit the evolution of female adaptations even if these reduce male fitness. We found additive genetic variation in signa length and width only in one population (BG); heritability estimates were high: 0.96 and 0.8, respectively. The existence of additive genetic variation in signa size could be, at least in part, a result of relaxed sexually antagonistic selection pressures due to the low level of polyandry exhibited by this species. Our results imply that there is currently potential for further sexual coevolution in this trait.

Quantitative genetic insights into the coevolutionary dynamics of male and female genitalia

“…Heritability values for both female and male genital length were high (h 2 ¼ 0.61 and h 2 ¼ 0.90, respectively), which, although unexpected for fitness traits under directional or stabilizing selection [72], is not without precedent in studies of genital traits [73] and other fitness traits [60]. These values may reflect high additive genetic variance (V A ) and/or correspondingly low residual variance in these traits [74], or violations of the assumption of autosomal inheritance, which would have inflated our estimates of V A [27,60].…”

The evolution of female genitalia

“…Ambriz, Mota, and Cordero (2011) used a different approach to try to detect an effect of sexual conflict on female genital evolution by looking for additive genetic variation in signa traits in the butterfly Callophrys xami. No significant additive genetic variation was found in components of signa shape, which is suggestive of an effect of directional selection driving evolution towards a particular shape (potentially via sexual conflict), thus removing genetic variation for this trait from the population (Ambriz et al, 2011). Interestingly, between two different populations, there were significant differences in a suite of traits, including signa width and three components of signa shape (Ambriz et al, 2011).…”

“…No significant additive genetic variation was found in components of signa shape, which is suggestive of an effect of directional selection driving evolution towards a particular shape (potentially via sexual conflict), thus removing genetic variation for this trait from the population (Ambriz et al, 2011). Interestingly, between two different populations, there were significant differences in a suite of traits, including signa width and three components of signa shape (Ambriz et al, 2011). A more recent study on the Indian meal moth (Plodia interpunctella) has found somewhat conflicting results.…”

Sexual Selection Within the Female Genitalia in Lepidoptera

“…Data from an investigation looking for additive genetic variance in the morphology of the spine-shaped signa of the butterfly C. xami (Jiménez et al 2011) found significant additive genetic variance for signa length and width in one of the two populations studied, and also (and more interesting from the point of view of the SAC hypothesis) significant extranuclear maternal effects on some components of size and shape of signa, which could facilitate the evolution of optimal signa size and shape, even if these female adaptations decrease male fitness. The SAC hypothesis (Cordero 2005) provides a relatively well-supported explanation for the evolutionary origin of signa (Sánchez et al 2011;Sánchez and Cordero 2014) and possibly for part of its diversity.…”