Supermales (YY sex chromosomes) and androgen-treated XY males: Competition for mating with female killifish Oryzias latipes

Abstract In daily competitions for mating, between matched pairs of males (one YY and one XY), the YY genotype was usually the victor and had higher mean values for individual components of male reproductive behaviour. After 183 tests of competition between pairs of untreated YY and XY males, with spawnings in 114 of these trials, tests were continued while the losing XY males were given testosterone propionate. During androgenic treatment the XY males induced more spawnings than YY males, i.e. became victors instead of losers. Also, while XY (but not YY) males received exogenous androgen, the XY males tended to score higher mean values for all but one of the components of male reproductive behaviour under study, whereas YY males tended to have reduced values. Data for individual pairs of fish were consistent with mean data for all pairs.