Morph-dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards <i>Buteo buteo</i>

How genetic polymorphisms are maintained in a population is a key question in evolutionary ecology. Previous work on a plumage colour polymorphism in the common buzzard Buteo buteo suggested heterozygote advantage as the mechanism maintaining the co-existence of three morphs (light, intermediate and dark). We took advantage of 20 years of life history data collected in a Dutch population to replicate earlier studies on the relationship between colour morph and fitness in this species. We examined differences between morphs in adult apparent survival, breeding success, annual number of fledglings produced and cumulative reproductive success. We found that cumulative reproductive success differed among morphs, with the intermediate morph having highest fitness. We also found assortative mating for colour morph, whereby assortative pairs were more likely to produce offspring and had longer-lasting pair bonds than disassortative pairs. Over the 20-year study period, the proportion of individuals with an intermediate morph increased. This apparent evolutionary change did not just arise from selection on individual phenotypes, but also from fitness benefits of assortative mating. The increased frequency of intermediates might also be due to immigration or drift. We hypothesize that genetic variation is maintained through spatial variation in selection pressures. Further studies should investigate morph-dependent dispersal behaviour and habitat choice

Inheritance patterns of plumage coloration in common buzzards <i>Buteo buteo</i> do not support a one-locus two-allele model

Balancing selection is a major mechanism to maintain colour polymorphisms over evolutionary time. In common buzzards, variation in plumage colour was reportedly maintained by a heterozygote advantage: heterozygote intermediates had higher fitness than homozygote light and dark morphs. Here, we challenge one of the basic premises of the heterozygote advantage hypothesis, by testing whether plumage colour variation in common buzzards follows a one-locus two-allele inheritance model. Using a long-term population study with 202 families, we show that colour variation in buzzards is highly heritable. However, we find no support for a simple Mendelian one-locus two-allele model of inheritance. Our results rather suggest that buzzard plumage colour should be considered a quantitative polygenic trait. As a consequence, it is unlikely that the proposed heterozygote advantage is the mechanism that maintains this genetic variation. We hypothesize that plumage colour effects on fitness might depend on the environment, but this remains to be tested

feeding1213

Contains the feeding rates of different prey types across age classe

fitnessR

R script to analyze effect of diet on components of fitness. Reads into the data file fitndiet1213.csv and feeding1213.cs

fitndiet1213

Contains measures of offspring condition and feeding rate

201213all

Principal file containing all the prey dat

diet_age

Contains the R script that uses the data file 1213all.csv to analyze dietary variation and make the graphs

Appendices 1 and 2; Figure S1 and Tables S1 and S2 from Inheritance patterns of plumage coloration in Common Buzzards <i>Buteo buteo</i> do not support a one-locus two-allele model

Appendix 1: Study site; Appendix 2: Colour morph scoring; Figure S1: Observed and expected inheritance of plumage colour morph for all parental combinations in Common Buzzards from Friesland, The Netherlands.; Table S1: Observed and expected inheritance of plumage colour morph for all parental combinations in Common Buzzards from Friesland, The Netherlands.; Table S2: Observed inheritance of plumage colour morph in Common Buzzards from Friesland, The Netherlands (our study), and from a previous study in Eastern Westphalia, German