Male sexual polymorphism, alternative reproductive tactics, and androgens in combtooth blennies (Pisces : Blenniidae)

In species in which intense intermale competition for the access to females is present males of lower competitive ability may adopt alternative reprod uctive tactics (ART) to get access to mates. These ART translate in many ca ses into male sexual polymorphism, with individuals following distinctly di fferent tactics. Usually two alternative male morphs can be recognized in s pecies with ART: (1) bourgeois males that compete for access to mates inves t in typically male behaviors, such as building elaborated nests or display ing ornaments; and (2) parasitic males that take advantage of the success o f the bourgeois males in attracting females and attempt "sneaker" fertiliza tions (e.g., sneaker and satellite males). In combtooth blennies (Blenniida e) the co-occurrence of ART and male sexual polymorphism has been described for two temperate species: the peacock blenny, Salaria pavo, and the Azore an rock-pool blenny, Parablennius sanguinolentus parvicornis. Interestingly , while in the peacock blenny the alternative male morph adopts a sneaker t actic, in the rock-pool blenny parasitic males act as satellites to nest-ho lder males. Thus, this variation in the ART expressed in these two closely related species allows for a comparative study of the proximate and ultimat e factors affecting the expression of the two ART. In this article we summa rize the available information on androgen levels in bourgeois and parasiti c males of natural populations of the two species and of recent studies on the effect of exogenous administration of androgens on tactic switching in parasitic males of the two species. The information is discussed within the frame of the relative plasticity hypothesis, which predicts that plastic a lternative morphs should show differences in hormone levels and that the ad ministration of sex steroids should be effective in promoting the switch fr om the parasitic to bourgeois tactic. The evidence is only partly consisten t with this hypothesis. Alternatively, a social transduction hypothesis tha t better fits the available data on androgens and ART in teleost is propose d. It states that the observed differences in androgen levels between alter native morphs should not be interpreted as an organization vs activation ef fect of steroids, but rather as the limited vs lifelong responsiveness of t he neuroendocrine axis to social regulation. (C) 2001 Academic Press.