Meeting Abstract

P2.5  Thursday, Jan. 5  Chirp parameters signal sex but not male quality in the weakly electric fish Parapteronotus hasemani PETZOLD, J.M.*; SMITH, G.T.; Indiana University, Bloomington; Indiana University, Bloomington jpetzold@indiana.edu

Apteronotid electric fish produce a continuous electric organ discharge (EOD) that functions in communication. The frequency and amplitude of the EOD can be modulated during reproductive and agonistic interactions to produce chirps. In several species, EOD frequency and chirping are sexually dimorphic traits that are regulated by steroid hormones. However, the signal parameters that differ between the sexes vary greatly among species. We tested how EOD frequency and chirping vary between and within sexes in Parapteronotus hasemani, a species of South American electric fish with extreme morphological sexual dimorphism in body size. P. hasemani males also show a great degree of within-sex variation in jaw morphology that may indicate age or social status (Cox Fernandes, 2010). We measured circulating concentrations of testosterone (T) and 11-ketotestosterone (11KT) as well as jaw length, body length, and body mass. We also performed playbacks of species-typical EODs to sixteen P. hasemani to quantify EOD frequency and chirping. The duration of chirps was longer in males than in females, although EOD frequency, chirp rate, and chirp amplitude modulation were sexually monomorphic. Circulating concentrations of T and 11KT were not correlated with jaw morphology, body size, or EOD frequency within males. Thus, chirp duration, but not EOD frequency, is a sexually dimorphic trait that may be used as an honest indicator of sex in P. hasemani. The lack of a correlation of EOD and chirp parameters with hormone levels or morphological traits within males, however, suggests that these signals may not necessarily serve as reliable indicators of male quality. Supported by NSF IOS 0950721.