LEARY, C.J.*; KNAPP, R.; University of Oklahoma; University of Oklahoma: Mating Tactic Expression and Selection of Hosts by Satellite Male Toads: Vocal and Hormonal Relationships

Alternative non-calling “satellite” tactics are adopted by males of numerous anuran species (frogs and toads), but the underlying physiological mechanisms mediating the behavioral response are poorly understood. Our research on Woodhouse’s toads (Bufo woodhousii) and Great Plains toads (Bufo cognatus) indicates that calling males have significantly higher levels of circulating corticosterone (B) than satellite males and high B is associated with depletion of energy reserves during vocal bouts (Leary et al. Behav. Ecol. in press). However, B does not have an inhibitory effect on androgen production, as predicted by recent models. Rather, in these two species, B may inhibit the release of arginine vasotocin (AVT) from vocal control centers of the brain and mediate the expression of satellite tactics. Moreover, an increase in circulating levels of B during reproductive activity is associated with a decrease in call duration and this relationship has been supported by preliminary hormone manipulation data. Host selection by satellite males is not related to differences in circulating levels of androgens. Here we show that satellite males not only parasitize host males with the longest calls (presumably to increase the probability of obtaining a mate) but also that this relationship corresponds with significantly higher circulating B levels in non-parasitized callers versus parasitized callers. Surprisingly, the reverse relationship exists with respect to circulating estradiol, a hormone that may affect call production by regulating AVT receptor number (e.g., Boyd, SK. 1997. Brain Res. Bull.). We are currently pursuing interactions among these various neuroendocrine factors as they relate to mediating the expression of male reproductive tactic. Research is supported by NSF and OCAST.