ARTIFICIAL SELECTION FOR INCREASED COMB SIZE AND ITS EFFECTS ON OTHERSEXUAL CHARACTERS AND VIABILITY IN GALLUS-DOMESTICUS (THE DOMESTIC CHICKEN)

The expression of secondary ornaments is often positively correlated w ith the bearer's condition. So far no study has reported on consequenc es of directional selection on male sexual ornaments in birds, i.e. it is unknown to what extent male sexual traits are genetically correlat ed and whether selection for secondary ornaments affects viability. In this study we estimate phenotypic and genotypic parameters of three m ale sexual traits, namely comb size, spur length and testes mass, by u sing two different lines of domestic chickens (Gallus domesticus). One of the two lines had been artificially selected for large comb size d uring nine generations whereas the other line was a randomly mated con trol line. As a result of the selection, male comb size was almost dou bled. Data from the selection line indicate that comb size was negativ ely genetically correlated with testes mass and spur length. The cocke rels from the selection line had accordingly lighter testes and shorte r spurs than cockerels from the control line. A simple mate choice exp eriment with females and males from both lines indicated that preferre d males had a larger joint expression of comb size and spur length tha n nonpreferred males. Data from three different selection lines, all w ith enlarged comb size, clearly reveal a negative effect of comb size on male viability.