Endocrine mediation of alternative mating tactics in toads: A proximate perspective on ecological patterns and sexual selection.

Abstract

Male Great Plains toads (Bufo cognatus) and Woodhouse's toads (Bufo woodhousii) alternate between one of two mating tactics; they may either vocalize to attract mates or they may adopt a non-calling "satellite" tactic. Alternation from the calling to the satellite tactic is associated with a reduction in body mass during chorus activity that drives an increase in circulating corticosterone levels. Elevation in corticosterone levels result in a progressive decrease in call duration that eventually leads to the cessation of calling activity and the expression of the alternative non-calling satellite tactic. Females prefer the calls characteristic of males with the lowest corticosterone levels, suggesting that selection may favor any heritable component associated with maintenance of relatively low corticosterone levels or suppression of the stress response. However, sexually-parasitic males practicing alternative reproductive tactics also prefer to associate with calling males with the lowest corticosterone levels that produce the longest calls. Hence, although calling males in the best physical condition with the lowest levels of corticosterone produce the most attractive calls, males with the longest calls may also experience a reduction in reproductive success by attracting sexually parasitic conspecific satellite males. Therefore, directional selection on preferred male traits via female choice may be countered by host selection via males practicing alternative mating tactics.