TESTOSTERONE LEVELS AND EVOKED VOCAL RESPONSES IN A NATURAL-POPULATION OF THE FROG BATRACHYLA-TAENIATA

Relationships between testosterone plasma levers and evoked vocal resp onses of males of the leptodactylid frog Batrachyla taeniata from sout hern Chile were studied. Evoked vocal responses were elicited in the f ield with playbacks of a synthetic imitation of the conspecific advert isement call and variants of this signal for which different temporal parameters were modified. Testosterone plasma levels were measured wit h radioimmunoassay in blood samples obtained from the experimental sub jects immediately after the playback experiments and from nonstimulate d males. Testosterone levels between groups did not differ significant ly. A significant correlation between testosterone concentration and n umber of calls given in response to the synthetic advertisement call w as found. Testosterone revels were also significantly correlated with the total number of calls given by the experimental subjects in respon se to the complete series of stimuli. Other measures of evoked vocal r esponses, i.e., number of pulses per call, call duration, pulse rate, and latency to first call, were not significantly correlated with test osterone revels. These results indicate a predominant effect of testos terone on the motivation of males of B. taeniata to call, rather than on the physical attributes of the vocalizations. (C) 1997 Academic Pre ss.