Natural and sexual selection against hybrid flycatchers

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 275; no. 1635; pp. 735 - 744
• Main Authors: Svedin, Nina, Wiley, Chris, Veen, Thor, Gustafsson, Lars, Qvarnström, Anna
• Format: Journal Article
• Language: English
• Published: London The Royal Society 22.03.2008
• Subjects: Animals; Assortative Mating; Biologi; Biology; Breeding; Ecological competition; Evolutionary genetics; Extra-Pair Paternity; Female; Female animals; Ficedula albicollis; Ficedula hypoleuca; Flycatchers; Hybrid Fitness; Hybridity; Hybridization, Genetic; Male; Male animals; Mating behavior; NATURAL SCIENCES; NATURVETENSKAP; Passeriformes - anatomy & histology; Passeriformes - physiology; Phenotype; Postzygotic Isolation; Principal Component Analysis; Reinforcement; Reproduction - physiology; Reproductive success; Selection, Genetic; Sexual selection; Speciation
• ISSN: 0962-8452; 1471-2954; 1471-2954
• DOI: 10.1098/rspb.2007.0967

While sexual selection is generally assumed to quickly cause or strengthen prezygotic barriers between sister species, its role in causing postzygotic isolation, through the unattractiveness of intermediate hybrids, is less often examined. Combining 24 years of pedigree data and recently developed species-specific molecular markers from collared (Ficedula albicollis) and pied (Ficedula hypoleuca) flycatchers and their hybrids, we were able to quantify all key components of fitness. To disentangle the relative role of natural and sexual selection acting on F1 hybrid flycatchers, we estimated various fitness components, which when combined represent the total lifetime reproductive success of F1 hybrids, and then compared the different fitness components of F1 hybrids to that of collared flycatchers. Female hybrid flycatchers are sterile, with natural selection being the selective force involved, but male hybrids mainly experienced a reduction in fitness through sexual selection (decreased pairing success and increased rate of being cuckolded). To disentangle the role of sexual selection against male hybrids from a possible effect of genetic incompatibility (on the rate of being cuckolded), we compared male hybrids with pure-bred males expressing intermediate plumage characters. Given that sexual selection against male hybrids is a result of their intermediate plumage, we expect these two groups of males to have a similar fitness reduction. Alternatively, hybrids have reduced fitness owing to genetic incompatibility, in which case their fitness should be lower than that of the intermediate pure-bred males. We conclude that sexual selection against male hybrids accounts for approximately 75% of the reduction in their fitness. We discuss how natural and sexual selection against hybrids may have different implications for speciation and conclude that reinforcement of reproductive barriers may be more likely when there is sexual selection against hybrids.