Regulation of Sex Differences in Communication Signals by Gonadal Steroid Hormones. EOD frequency and chirping are sexually dimorphic in many species of electric fish, but the magnitude and the direction of sex differences varies across species. In brown ghost knifefish (A. leptorhynchus), males have higher EOD frequency and chirp 10-20 times more often than females. In some populations of black ghost knifefish (A. albifrons), males have lower EOD frequency than females, and chirping is much less sexually dimorphic (Dunlap et al. 1998; Kolodziejski et al. 2005). In other species, like pig-duck knifefish (P. hasemani) and dragon knifefish (“A.” bonapartii), EOD frequency does not differ across sexes (Ho et al. 2010; Petzold and Smith 2016). Sex differences in EOD frequency and chirping are regulated by hormones like 11-ketotestosterone (11-KT) and estradiol. The effects of these hormones vary between species in parallel with species differences in sexual dimorphism. 11-KT masculinizes EOD frequency in both A. leptorhynchus and sexually dimorphic populations of A. albifrons, but does so by raising EOD frequency in A. leptorhynchus, but lowering EOD frequency in A. albifrons (Dunlap et al. 1998; Ho et al. 2013). The effects of androgens and estrogens on EOD frequency are mediated largely by effects of these hormones on the firing rates of neurons in the pacemaker nucleus and electromotor neurons in the spinal cord (Schaefer and Zakon 1997). The effects of hormones on behavior can also be influenced by how hormones are metabolized in the brain.
We study how steroid hormones affect sex and species differences in electrocommunication behavior by using several techniques:
(1) Treating different species and populations of fish with androgens and estrogens to determine how hormonal effects on EOD frequency and chirping influence sexual dimorphism of these signals.
(2) Measuring levels of hormones in relation to sex, reproductive condition, social dominance, and electrocommunication behavior in different species.
(3) Treating different species and populations with drugs that block androgen or estrogen receptors or the enzymes that metabolize them to more/less active forms to assess how metabolism and actions of these hormones evolve and influence sex differences in these signals.
(4) Combining hormone treatments with electrophysiology to study the effects of androgens and estrogens on the firing patterns and excitability of the neurons that control the EOD and chirping.
References
Dunlap, K.D., Thomas, P., and Zakon, H.H. (1998) Diversity of sexual dimorphism in electrocommunication signals and its androgen regulation in a genus of electric fish, Apteronotus. J. Comp. Physiol. A 183:77-86.
Ho, W.W., Fernandes, C.C., Alves-Gomes, J.A., and Smith, G.T. (2010) Sex differences in the electrocommunication signals of the electric fish Apteronotus bonapartii. Ethology 116:1050-1064.
Ho, W.W., Rack, J.M., and Smith, G.T. (2013) Divergence in androgen sensitivity contributes to population differences in sexual dimorphism of electrocommunication behavior. Horm. Behav. 63:49-53.
Kolodziejski, J.A., Nelson, B.S., and Smith, G.T. (2005) Sex and species differences in neuromodulatory input to a premotor nucleus: a comparative study of substance P and communication behavior in weakly electric fish. J. Neurobiol. 62:299-315.
Petzold, J.M. and Smith, G.T. (2016) Androgens regulate sex differences in signaling but not male variation in the weakly electric fish Parapteronotus hasemani. Horm. Behav. 78:67-71.
Schaefer, J. and Zakon, H.H. (1997) Opposing actions of androgen and estrogen on in vitro firing frequency of neuronal oscillators in the electromotor system. J. Neurosci. 16:2860-2868.
Electric Fish Lab 