Inbreeding depression plays a major role in shaping mating systems: in particular, inbreeding avoidance is often proposed as a mechanism explaining extra‐pair reproduction in socially monogamous species. This suggestion relies on assumptions that are rarely comprehensively tested: that inbreeding depression is present, that higher kinship between social partners increases infidelity, and that infidelity reduces the frequency of inbreeding. Here, we test these assumptions using 26 years of data for a cooperatively breeding, socially monogamous bird with high female infidelity, the superb fairy‐wren (Malurus cyaneus). Although inbred individuals were rare (∼6% of offspring), we found evidence of inbreeding depression in nestling mass (but not in fledgling survival). Mother–son social pairings resulted in 100% infidelity, but kinship between a social pair did not otherwise predict female infidelity. Nevertheless, extra‐pair offspring were less likely to be inbred than within‐pair offspring. Finally, the social environment (the number of helpers in a group) did not affect offspring inbreeding coefficients or inbreeding depression levels. In conclusion, despite some agreement with the assumptions that are necessary for inbreeding avoidance to drive infidelity, the apparent scarcity of inbreeding events and the observed levels of inbreeding depression seem insufficient to explain the ubiquitous infidelity in this system, beyond the mother–son mating avoidance.
Postcopulatory sexual selection is an important force in the evolution of reproductive traits, including sperm morphology. In birds, sperm morphology is known to be highly heritable and largely condition-independent. Theory predicts, and recent comparative work corroborates, that strong selection in such traits reduces intraspecific phenotypic variation. Here we show that some variation can be maintained despite extreme promiscuity, as a result of opposing, copulation-role-specific selection forces. After controlling for known correlates of siring success in the superb fairy-wren (Malurus cyaneus), we found that (a) lifetime extra-pair paternity success was associated with sperm with a shorter flagellum and relatively large head, and (b) males whose sperm had a longer flagellum and a relatively smaller head achieved higher within-pair paternity. In this species extrapair copulations occur in the same morning, but preceding, pair copulations during a female's fertile period, suggesting that shorter and relatively larger-headed sperm are most successful in securing storage (defense), whereas the opposite phenotype might be better at outcompeting stored sperm (offense). Furthermore, since cuckolding ability is a major contributor to differential male reproductive output, stronger selection on defense sperm competition traits might explain the short sperm of malurids relative to other promiscuous passerines.
The challenge in defining conservation units so that they represent evolutionary entities has been to combine both genetic properties and ecological significance. Here we make use of the complexity of the European Alps, with their genetic landscape shaped by geographical barriers and postglacial colonization, to examine the correlation between ecological and genetic divergence. Montane species, because of the fragmentation of their present habitat, constitute extreme cases in which to test if genetically distinct subgroups based on neutral markers are also ecologically differentiated and show local adaptation. In the leaf beetle Oreina elongata , populations show variation in host plant use and a patchy distribution throughout the Alps and Apennines. We demonstrate that despite very strong genetic isolation ( F ST = = = = 0.381), variation in host plant use has led to differences in larval life-history traits between populations only as a secondary effect of host defence chemistry, and not through physiological adaptation to plant nutritional value. We also establish that populations that are more ecologically different in terms of larval performance are also more genetically divergent. In addition, morphological variation used to define subspecies appears to be mirrored in the population genetics of this species, resulting in almost perfect clustering based on microsatellite data. Finally, we argue from their strong genetic structure and congruent distribution that the subspecies of O. elongata were divided among the same glacial refugia within the Alps that have been proposed for alpine plants.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.