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

The size and shape of the cockerel comb, ran be regarded as secondary sexua l characters or sexual ornaments. Sexual characters are assumed to be costl y to express and the expression of a secondary sexual character is suggeste d to be favourably correlated with the bearer's condition or fitness. The a im of this study was to clarify the effects of selection for male sexual ch aracters, the correlated responses in other male traits and whether selecti on for sexual characters affects viability. Two selection lines (lines S an d H) and a control line was used for 10 generations. Line S was selected fo r male comb size at 29 weeks of age and from generation six onwards, comb s hape (the way the cockerel bear his comb) was added. Line H was selected fo r 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 t he randomly mated control line comprised an average of 150 animals of each sex per generation. Traits recorded an analysed were comb size (CS) and bod y 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 p henotypic trends increased for CS, CW and BW. Both CS and SH are traits inv olved in the impression of comb size as visualized by females during male c hoice and by males during male-male competition. With artificial upward sel ection 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, th e negative generic trend for SH was changed to positive. As CS approaches i ts environmental limit, the heritability and genetic progress can be expect ed to decline. It seems that 10 generations of selection for increased CS i s not enough to reach the environmental limit at which CS is expected to st abilize at an optimum size determined by natural selection.