Endocrine Regulation of Dynamic Communication Signals in Gymnotiform Fish

Abstract

between an inconspicuous signal that evades predators and an extravagant signal preferred by females. Such a signal has been described in the gymnotiform electric fish, Brachyhypopomus gauderio, which produces a sexually dimorphic electric organ discharge (EOD). The EOD varies on a circadian rhythm and in response to social cues. This signal plasticity is mediated by the slow action of androgens and rapid action of melanocortins.My dissertation research tested the hypotheses that (1) signal plasticity is related to sociality levels in gymnotiform species, and (2) differences in signal plasticity are regulated by differential sensitivity to androgen and melanocortin hormones. To assess the breadth of dynamic signaling within the order Gymnotiformes, I sampled 13 species from the five gymnotiform families. I recorded EODs to observe spontaneous signal oscillations after which I injected melanocortin hormones, saline control, or presented the fish with a conspecific. I showed that through the co-option of the ancient melanocortin vii pathway, gymnotiforms dynamically regulate EOD amplitude, spectral frequency, both, or neither.To investigate whether observed EOD plasticities are related to species-specific sociality I tested four species; two territorial, highly aggressive species, Gymnotus carapo and Apteronotus leptorhynchus, a highly gregarious species, Eigenmannia cf. virescens, and an intermediate short-lived species with a fluid social system, Brachyhypopomus gauderio. I examined the relationship between the androgens testosterone and 11-ketotestosterone, the melanocortin α-MSH, and their roles in regulating EOD waveform.

The energetics of electric organ discharge generation in gymnotiform weakly electric fish

“…virescens and Apteronotus albifrons, females display higher EOD baseline frequencies than males (Hopkins, 1972;Hopkins, 1974;Dunlap et al, 1998), and the opposite is true in A. leptorhynchus (Dunlap et al, 1998). In addition, in several gymnotiform species from the Rhamphichthyidae, Hypopomidae and Sternopygidae families, individuals can alter their EOD waveforms reversibly within minutes to hours (Table1) (Silva et al, 1999;Franchina and Stoddard, 1998;Markham et al, 2009;Goldina, 2011). For instance, the EOD waveforms of B. gauderio are enhanced from day to night, following a circadian rhythm (Franchina and Stoddard, 1998;Stoddard et al, 2007).…”