Greenfinch plumage varies both between and within age and sex classes. This study looked at the possible causes and consequences of this variation in a colour-ringed population. Plumage colour was both repeatable and heritable. The function of colourful plumage in the breeding season was reviewed. Many aspects of the breeding biology of Greenfinches were studied and the effects of plumage on breeding success investigated. Brightly coloured birds seemed to have greater reproductive success than dull ones. Brightly coloured males were also more likely to ret urn to the study area in the following breeding season. Greenfinches are usually regarded as monogamous, but I found that over 25% of nests involved polygamy. Polygyny, polyandry and possible cases of polygynandry were recorded, but polygyny was the most common of the three. It was demonstrated that the experimental provision of food influenced the occurrence of polygyny. The literature generally considers polygyny to be bad for females, however in Greenfinches polygynous pairs were as successful at producing independent offspring as monogamous pairs. Polygynous birds recruited more offspring into the local population than monogamous birds, although this may reflect differences in dispersal. Since polygynous males were bright and had better survival and since colour was found to be heritable, females may have been choosing males for their good genes. If colour is an honest signal, there must be some cost preventing dull birds from becoming bright. Bright Greenfinches were more likely to be killed by Sparrowhawks during the summer than dull Greenfinches and they were also more likely to be injured. In comparison, dull birds were more likely to be killed by Tawny Owls in the winter. Whether Greenfinch plumage variation acted as a "badge of status" over the winter was investigated. The brighter a Greenfinch's plumage the more likely it was to win confrontations at a bird table in the winter, regardless of food type (contra Maynard Smith & Harper 1988). So what influenced a Greenfinch's plumage? Birds with damaged feathers only regrew bright plumage if they were in good body condition. Birds with low fat stores regrew paler feathers after damage, which is possibly related to the fact that the carotenoid pigment is stored in fat. Therefore, it is possible that after the breeding season good quality nales recovered faster, put on more fat and acquired brighter plumage in the moult. Plumage variation in the House Sparrow was also investigated. In hand estimates of bib size were correlated with spectrophotometric estimates of melanin content. Bib size was not related to organ size. The results of this study are compared with the literature on status signalling . It is argued that badges are handicaps i.e. uncheatable signals of individual quality, rather than being arbitrary signals or signalling Resource Holding Potential.

Domestication is the process by which animals become adapted to the environment provided by humans. The process of domestication has let to a number of correlated behavioural, morphological and physiological changes among many domesticated animal species. An example is the changes of plumage colour in the chicken. Plumage colour is one of the most readily observable traits that make distinction between breeds as well as between strains within a breed. Understanding the genetic architecture of pigmentation traits or indeed any trait is always a great challenge in evolutionary biology. The main aim of this study was to map quantitative trait loci (QTLs) affecting the red and metallic green coloration in the chicken plumage. In this study, a total of 572 F8 intercross chickens between Red Junglefowl and White Leghorn were used. Phenotypic measurements were done using a combination of digital photography and photography manipulating software. Moreover, all birds were genotyped with 657 molecular markers, covering 30 autosomes. The total map distance covered was 11228 cM and the average interval distance was 17 cM. In this analysis, a total of six QTLs (4 for red and 2 for metallic green colour) were detected on four different chromosomes: 2, 3 11 and 14. For red colour, the most significant QTL was detected on chromosome 2 at 165 cM. An additional QTL was also detected on the same chromosome at 540 cM. Two more QTLs were detected on chromosomes 11 and 14 at 24 and 203 cM respectively. Additionally, two epistatic pairs of QTLs were also detected. The identified four QTLs together can explain approximately 36% of the phenotypic variance in this trait. In addition, for metallic green colour, one significant and one suggestive QTLs were detected on chromosomes 2 and 3 at 399 and 247 cM respectively. Moreover, significant epistatic interactions between these two QTLs were detected. Furthermore, these two QTLs together can explain approximately 24% of the phenotypic variance in this trait. These findings suggest that the expression of pigmentation in the chicken plumage is highly influenced by both the epistatic actions and pleiotropic effects of different QTLs located on different chromosomes.

<p>The purpose of gene mapping is to understand the underlying genetics of simple and complex traits like plumage colour and growth. This thesis is based on a cross between the wild ancestor of the modern chicken, the red junglefowl, and a White Leghorn line selected for high egg mass. There are obvious phenotypic differences between these two breeds in several aspects such as growth, egg production and behaviour. These complex traits are often influenced by a number of genes or Quantitative Trait Loci (QTL) as well as environmental factors.</p><p>Identification of QTL regions involves testing of association between genetic markers and the phenotype of interest. The QTL identified in this study explain most of the difference in adult body weight between the red junglefowl and the White Leghorn, but less of the difference at earlier age. By applying a different method for detection of QTL, including gene interactions, epistasis, we can understand more of the genetics behind early growth. The allele coming from the red junglefowl is generally associated with lower weight, egg production and food consumption.</p><p>In this study we have also identified two genes explaining the difference in plumage colour in the cross. The <i>Extension</i> locus, encoded by the melanocortin receptor 1 (<i>MC1R</i>), controls the amount of pigment produced has shown to be associated with plumage colour. A mutation in the <i>MC1R</i> gene causes black pigmentation of the plumage. </p><p>We have also found association between the <i>PMEL17</i> gene, known to be involved in normal pigmentation, and the <i>Dominant white</i> phenotype present in the White Leghorn. After comparison of sequences from different alleles at the <i>Dominant white</i> locus, amino acid alteration caused by insertion and deletion in the transmembrane region of the <i>PMEL17</i> protein has been revealed. These mutations are associated with alleles representing different plumage colour variants.</p>

The purpose of gene mapping is to understand the underlying genetics of simple and complex traits like plumage colour and growth. This thesis is based on a cross between the wild ancestor of the modern chicken, the red junglefowl, and a White Leghorn line selected for high egg mass. There are obvious phenotypic differences between these two breeds in several aspects such as growth, egg production and behaviour. These complex traits are often influenced by a number of genes or Quantitative Trait Loci (QTL) as well as environmental factors. Identification of QTL regions involves testing of association between genetic markers and the phenotype of interest. The QTL identified in this study explain most of the difference in adult body weight between the red junglefowl and the White Leghorn, but less of the difference at earlier age. By applying a different method for detection of QTL, including gene interactions, epistasis, we can understand more of the genetics behind early growth. The allele coming from the red junglefowl is generally associated with lower weight, egg production and food consumption. In this study we have also identified two genes explaining the difference in plumage colour in the cross. The Extension locus, encoded by the melanocortin receptor 1 (MC1R), controls the amount of pigment produced has shown to be associated with plumage colour. A mutation in the MC1R gene causes black pigmentation of the plumage. We have also found association between the PMEL17 gene, known to be involved in normal pigmentation, and the Dominant white phenotype present in the White Leghorn. After comparison of sequences from different alleles at the Dominant white locus, amino acid alteration caused by insertion and deletion in the transmembrane region of the PMEL17 protein has been revealed. These mutations are associated with alleles representing different plumage colour variants.