Development and maintenance of quality indicators in pheasants

Abstract: Females often base their choice of mates on the expression, size or intensity, of male sexual ornaments. Indicator models of sexual selection assume that females assess male genetic quality through the expression of these secondary sexual characters. Several mechanisms that link the expression of sexual ornaments to genetic quality have been suggested. Many models assume that this link is individual genetic quality that modifies environmental effects on condition, with males in higher condition developing larger ornaments. There are several different mechanisms by which condition may feed back on ornament expression. First, nutritional conditions during early development may cause persistent effects on the quality of individuals, which in turn may affect the later development of sexual ornaments. Second, males may vary in their ability to obtain food during the period when ornaments are developed or maintained, which may affect ornaments either directly if they are dependent on limited nutrients, or indirectly via effects on male condition. Third, condition may be related to differences in the immune defence system, which in turn may affect the expression of ornaments. In this thesis I use the highly polygynous and sexually dimorphic ring-necked pheasant (Phasianus colchicus) to investigate the relative importance of nutrition during different ages for the development of quality indicators. Thus, I was interested in the consequences of early nutrition for the later quality and ornamentation of males, as well as the consequences of nutrition during adulthood for the expression of ornaments. In addition, I was interested in the interconnections between nutrition, ornament expression and immunological capacity. Pheasants have an array of sexual characters, of which I have studied only a few. These male traits seem to be signals of different aspects of male quality. On the one hand, characteristics of the wattles function as sensitive ornaments, that reliably reveals both earlier (size and colourfulness) and present (colourfulness) nutritional condition. Spur length, on the other hand, is an ornament that was not especially sensitive to my manipulation of food regimes, but instead seemed to be a reliable signal of a heritable capability of the immune system. Other measures of quality in birds, are the effect of nutritional constraints during early development on both growth and fluctuating asymmetry in final tarsus length, which may reveal information of general genetic quality.