Hormone-induced and maturational changes in electric organ discharges and electroreceptor tuning in the weakly electric fishApteronotus

Abstract

Plasticity in the frequency of the electric organ discharge (EOD) and electroreceptor tuning of weakly electric fish was studied in the genus Apteronotus. Both hormone-induced and maturational changes in EOD frequency and electroreceptor tuning were examined. Apteronotus is different from all other steroid-responsive weakly electric fish in that estradiol-17 beta, rather than androgens, induces discharge frequency decreases. This result can account for the 'reversed' discharge frequency dimorphism found in Apteronotus in which, counter to all other known sexually dimorphic electric fish, females have lower discharge frequencies than males. Studies of electroreceptor tuning in Apteronotus indicate that electroreceptors are closely tuned to the frequency of the EOD. This finding was noted not only in adult animals, but also in juvenile animals shortly after the onset of their EODs. Tuning plasticity in Apteronotus, as in other species studied, is associated with altered EOD frequencies and was noted in both maturational EOD changes and in estrogen-induced changes. Thus, tuning plasticity appears to be a general phenomenon which occurs concurrent with a variety of EOD changes.

Estrogen Modifies an Electrocommunication Signal by Altering the Electrocyte Sodium Current in an Electric Fish,Sternopygus

“…In contrast to Sternopygus, Apteronotus leptorhynchus (Meyer et al, 1987;Schaefer and Zakon, 1996) lower their EOD frequency in response to estradiol implantation. Preliminary evidence suggests that Apteronotus albifrons and Eigenmannia sp.…”

Energetic constraints on electric signalling in wave-type weakly electric fishes

“…Even though EOD frequency of wave-type fish can be extremely stable on time scales of hours, it can be modulated rapidly and transiently under the control of pre-pacemaker nuclei for purposes of communication (Metzner, 1999;Zakon et al, 2002). Slower changes on the time scale of development and sexual maturation have been shown to be under the control of steroid hormones (Meyer et al, 1983;Meyer et al, 1987;Zakon et al, 1991;Dunlap and Zakon, 1998), affecting voltage-gated sodium and potassium channels in the electrocytes (Ferrari et al, 1995;McAnelly and Zakon, 2007). Given that the kinetics of sodium and potassium Zakon, 2007), it appears likely that the kinetics are matched for a given EOD frequency to minimize sodium waste current (Hasenstaub et al, 2010).…”

Evolution and hormonal regulation of sex differences in the electrocommunication behavior of ghost knifefishes (Apteronotidae)

“…Apteronotid species vary in both the magnitude and direction of sexual dimorphism in EODf. The brown ghost knifefish (Apteronotus leptorhynchus) has a robust sex difference in EODf in the opposite direction to that of other knifefishes; males have higher EODf than females Hagedorn and Heiligenberg, 1985;Meyer et al, 1987). In contrast, male black ghost knifefish (Apteronotus albifrons) have lower EODfs than females .…”