Background Postzygotic isolation in the form of reduced viability and/or fertility of hybrids may help maintain species boundaries in the face of interspecific gene flow. Past hybridization events between ...

Background Female promiscuity is highly variable among birds, and particularly among songbirds. Comparative work has identified several patterns of covariation with social, sexual, ecological and life history ...

Background Several life history and ecological variables have been reported to affect the likelihood of species becoming urbanized. Recently, studies have also focused on the role of brain size in explaining ...

Background Evolutionary biology endeavours to explain biological diversity, and as such it is critical to develop an understanding of the adaptive and functional significance of trait variation. Spermatozoa ...

Birds show considerable variation in sperm morphology. Closely related species and subspecies can show diagnostic differences in sperm size. There is also variation in sperm size among males within a population, and recent ...

Sperm morphology is highly diversified across the animal kingdom and recent comparative evidence from passerine birds suggests that postcopulatory sexual selection is a significant driver of sperm evolution. In the present ...

Theoretical models predict that investment in pre-copulatory and post-copulatory sexually selected traits should trade-off. At the macroevolutionary scale, the majority of studies to date have focused on male weaponry as ...

Speciation research has largely overlooked reproductive barriers acting between copulation and the formation of the zygote (i.e., postmating, prezygotic [PMPZ] barriers), especially in internally fertilizing vertebrates. ...

Male fertilization success depends on investment in both pre- and postcopulatory sexually selected traits, and considerable attention has recently been paid to quantifying the strength and direction of covariance between ...

Sperm exhibit extraordinary levels of morphological diversification across the animal kingdom. In songbirds, sperm have a helically shaped head incorporating a distinct acrosomal membrane or “helical keel,” the form and ...