Reproductive success and male traits in the spotless starling, Sturnus unicolor

Abstract

Selection operates when the variability among individuals in heritable traits translates to differences in the number of offspring that survive to breed, which is a close estimate of fitness. Consequently, the outcome of sexual-selection should be higher reproductive success for individuals with a greater expression of the selected traits. In this thesis, the relationship between some male spotless starling (Sturnus unicolor) traits and reproductive success was assessed. A particular focus was given to the role of throat feathers (TF) as sexually selected trait. The study was conducted in a wild population using a correlative approach in 2004, while in 2005 and 2006 the TF of males were experimentally shortened. The genetic parentage of the offspring was required for determining the reproductive success of males. Nine highly polymorphic microsatellites (with 11.7± 3.2 alleles per locus) were developed and optimised for this species. Parentage analyses were conducted in NEWPAT XL and CERVUS 3.0.3 and confirmed using observational data. Eighty-five percent of the offspring had at least one parent assigned. The levels of intra-specific brood parasitism, extra-pair paternity and quasi-parasitism were 7%, 7% and 1% of the offspring, respectively. Polygamy levels decreased with year, as the study population matured. The correlative study showed that males with longer TF and with better condition had a higher probability of reproducing and sired more offspring, but their offspring were not of higher quality as measured by their weight and immune response to phytohaemagglutinin. Polygynous males were also in better condition. In the experimental study, males in better condition had a higher chance of reproducing and sired more fledglings. Conversely, males with reduced TF sired significantly fewer eggs and lighter fledglings than control males. Body condition and TF length are shown to be good predictors of reproductive success and TF length is shown to be under sexual selection.