This dissertation is about female promiscuity in passerine birds. By using comparative analytical approaches, I have tried to determine why there is such variation in the frequency of this behaviour. I have found that promiscuous species/populations have higher genetic diversity both at neutral loci and at loci directly involved in the recognition of pathogens. These observations may point to benefits from heterozygosity-fitness correlation or increased immunocompetence in offspring. The correlation between female promiscuity and genetic diversity may be driven by confounding variables. I evaluate one such potential confounding variable (covariate of female promiscuity), namely migration distance, but found that female promiscuity and migration distance correlates with different types of genetic diversity (autosomal and Z-linked intronic diversity respectively). Female promiscuity is a mating strategy that varies greatly in frequency in passerines. I found that the level of female promiscuity seem to differ among closely related populations of Cyanistes tits, and that these differences were independent of phylogeny. The hypothesis that female promiscuity predicts sperm lengths was not supported for this Cyanistes dataset. At a broader phylogenetic level (95 passerine spp., 27 families), I observed substantial variation in female promiscuity. In this larger dataset I identify a strong phylogenetic signal, which means that closely related species are similar in their frequency of female promiscuity. Hence, a substantial proportion of variation in female promiscuity will lie among families of Passeriformes. Variation at this phylogenetic level is likely associated with fundamental differences in ecology, while differences among species are likely related to genetic factors. Variation in female promiscuity could also be explained by genetic diversity being more or less beneficial for different species. Using the dataset of 95 spp., I evaluate the hypothesis that parasite pressure selects for increased promiscuity, because female promiscuity may increase immunocompetence in young. I found no evidence for a direct link between parasites and female promiscuity, but the proportion of animal matter in diet (a potential proxy for parasite exposure) was positively correlated with female promiscuity. An alternate evolutionary scenario that may explain the variation in female promiscuity is one where the benefits associated with promiscuous behaviour are universal, but the extent to which the behaviour is practiced is constrained by some factor. I describe a significant negative relationship between male parental care and female promiscuity and I discuss whether it may function as a constraint of female promiscuity. Given its link to genetic diversity, female promiscuity may be of importance for the adaptability and viability of populations. Thus, a thorough understanding of this phenomenon is interesting, not only to evolutionary biologists and ecologist, but also in conservation.
List of papers. The papers are removed from the thesis due to publisher restrictions.
Gohli J, Anmarkrud JA, Johnsen A, Kleven O, Borge T & Lifjeld, JT. 2013. Female promiscuity is positively associated with neutral and selected genetic diversity in passerine birds. Evolution. 67(5):1406-1419 doi:10.1111/evo.12045
Spurgin LG. 2013. Comment on Gohli et al. (2013): "Does promiscuity explain differences in levels of genetic diversity across passerine birds?" Evolution. 67(10):3071–3072 doi:10.1111/evo.12212
Lifjeld JT, Gohli J, Johnsen A. 2013. Promiscuity, sexual selection, and genetic diversity: A reply to Spurgin. Evolution. 67(10):3073-3074 doi:10.1111/evo.12211
Gohli J, Lifjeld JT & Albrecht T. Migration distance is positively associated with sexlinked genetic diversity in passerine birds. Manuscript.
Gohli J, Leder E, Garcia-del-Rey E, Johannessen LE, Johnsen A, Laskemoen T, Popp M, Lifjeld JT. Resolution of an enigmatic avian island radiation by genome-wide marker analyses. Manuscript.
Gohli J, Johnsen A & Lifjeld JT. Female promiscuity in passerine birds is dependent on phylogeny and associated with male parental care and diet. Manuscript.