Effects of androgens on social behavior and morphology of alternative reproductive males of the azorean rock-pool blenny

In the Azorean rock-pool blenny Parablennius sanguinolentus parvicornis two sequential reproductive tactics occur. Larger and older males establish br eeding territories, while some of the smaller males become attached to nest -holder territories, acting as satellites on these territories, which they help to defend while trying parasitic fertilizations when females go in the nests to spawn, In the present paper we tested the effects of the androgen s 17 alpha -methyltestosterone (MT) and 11-ketotestosterone (KT) in the exp ression of male secondary sex characters and bourgeois behavior in satellit e males. One week after satellites were implanted with Silastic tubes conta ining MT, KT, or castor oil (control), androgen-treated satellites had deve loped male secondary sex traits such as longer and wider male-type genital papilla and anal glands that secrete a sex pheromone, both traits being les s expressed or absent, respectively, in satellite males. Androgen treatment had no effect on the gonadosomatic index or on the development of the test icular gland. KT treatment had a positive effect on relative liver weight. In terms of behavior, androgen-implanted individuals were less aggressive b oth in a mirror test and toward females when these were introduced into the ir tanks. MT-treated individuals spend more time inside the provided nests. Only androgen-implanted satellites managed to have the females entering th eir nests. When given a chance in a group tank either to try to attract fem ales to their own nest or to act as satellites of an already established ne st-holder's nest, MT-implanted males spent significantly more time in their own nest than near the nest-holder nest. These data suggest that androgens , particularly testosterone, may be involved in mating tactic switching in this species. (C) 2001 Academic Press.