CONSTRAINTS ON THE EVOLUTION OF ATTRACTIVE TRAITS - GENETIC (CO)VARIANCE OF ZEBRA FINCH BILL COLOR

We estimated the heritability and genetic correlation between male and female bill colour in a laboratory population of zebra finches (Taeni opygia guttata) in order to examine the potential genetic constraints on the evolution of a sexually dimorphic trait. The heritability estim ates of bill colour from regressions of offspring on single parents ra nged from h2 = 0.34 to 0.73 and all but one of these estimates were si gnificantly greater than zero. The restricted maximum likelihood herit ability estimates for full- and half-siblings were significant for fem ales (h2 = 0.48) but not significant for males (h2 = 0.45). The maximu m likelihood estimates indicate that there is little dominance genetic variance for bill colour. The large genetic correlation between male and female bill colour (r(g) = 0.91) combined with opposing selection on male and female bill colour indicates that the evolution to sex-spe cific optima may proceed very slowly.