Selection for sexual male characters and their effects on other fitness related traits in white leghorn chickens

Abstract:
The size and shape of the cockerel comb, ran be regarded as secondary sexual characters or sexual ornaments. Sexual characters are assumed to be costly to express and the expression of a secondary sexual character is suggested to be favourably correlated with the bearer's condition or fitness. The aim of this study was to clarify the effects of selection for male sexual characters, the correlated responses in other male traits and whether selection for sexual characters affects viability. Two selection lines (lines S and H) and a control line was used for 10 generations. Line S was selected for male comb size at 29 weeks of age and from generation six onwards, comb shape (the way the cockerel bear his comb) was added. Line H was selected for high concentration of hyaluronic acid (HA) in the comb at 28 weeks of age. The average number of animals of each sex and;election line was 560 and the randomly mated control line comprised an average of 150 animals of each sex per generation. Traits recorded an analysed were comb size (CS) and body weight (BW) at 29 weeks of age, comb shape (SH) at 32 weeks of age, comb weight (CW) after slaughter and mortality (M). In line S, the genetic and phenotypic trends increased for CS, CW and BW. Both CS and SH are traits involved in the impression of comb size as visualized by females during male choice and by males during male-male competition. With artificial upward selection for the male character CS (line S), CS, CW, BW and M also increased but SH was impaired. When adding SH to the selection criteria in line S, the negative generic trend for SH was changed to positive. As CS approaches its environmental limit, the heritability and genetic progress can be expected to decline. It seems that 10 generations of selection for increased CS is not enough to reach the environmental limit at which CS is expected to stabilize at an optimum size determined by natural selection.