Behavioral ecology, endocrinology and signal reliability of electric communication

Abstract

SummaryThe balance between the costs and benefits of conspicuous animal communication signals ensures that signal expression relates to the quality of the bearer. Signal plasticity enables males to enhance conspicuous signals to impress mates and competitors and to reduce signal expression to lower energetic and predation-related signaling costs when competition is low. While signal plasticity may benefit the signaler, it can compromise the reliability of the information conveyed by the signals. In this paper we review the effect of signal plasticity on the reliability of the electrocommunication signal of the gymnotiform fish Brachyhypopomus gauderio. We (1) summarize the endocrine regulation of signal plasticity, (2) explore the regulation of signal plasticity in females, (3) examine the information conveyed by the signal, (4) show how that information changes when the signal changes, and (5) consider the energetic strategies used to sustain expensive signaling. The electric organ discharge (EOD) of B. gauderio changes in response to social environment on two time scales. Two hormone classes, melanocortins and androgens, underlie the short-term and long-term modulation of signal amplitude and duration observed during social interaction. Population density drives signal amplitude enhancement, unexpectedly improving the reliability with which the signal predicts the signalerʼs size. The signalʼs second phase elongation predicts androgen levels and male reproductive condition. Males sustain signal enhancement with dietary intake, but when food is limited, they ʻgo for brokeʼ and put extra energy into electric signals. Cortisol diminishes EOD parameters, but energy-limited males offset cortisol effects by boosting androgen levels. While physiological constraints are sufficient to maintain signal amplitude reliability, phenotypic integration and signaling costs maintain reliability of signal duration, consistent with theory of honest signaling. on the reliability of the information conveyed by the signal. In this paper, we (1) discuss the endocrine mechanisms that regulate signal plasticity in males, (2) explore whether those mechanisms are also present in females, (3) examine the information conveyed by the signal, (4) examine how that information changes when the signal changes, and finally (5) consider the energetic strategies used to sustain expensive signaling.

Electrocyte physiology: 50 years later

“…The cellular-level interaction of slow steroid effects and faster peptidergic regulation appears to be the primary mechanism through which EOD waveform carries important information about the sex, identity, social history and condition of the signaler. Gavassa and colleagues in this issue (Gavassa et al, 2013) address in detail the endocrine mechanisms that encode and integrate ecological history, seasonal variables, social cues and current conditions to determine relevant EOD waveform characteristics. No studies to date, however, have directly investigated at the electrocyte level how exactly steroid and peptide hormones interact to co-regulate the electrocyte discharge.…”

Neuromodulation of the agonistic behavior in two species of weakly electric fish that display different types of aggression

“…The spatial organization and innervation pattern of the peripheral electric organ are responsible for the species-specific EOD waveform (TrujilloCenóz et al, 1984;Stoddard, 2002). Brachyhypopomus gauderio, but not G. omarorum, exhibits a sustained nocturnal increase of EOD rate (Fig.1), along with a circadian rhythmicity of EOD waveform, both of which vary seasonally and are dependent on social context (Franchina and Stoddard, 1998;Franchina et al, 2001;Silva et al, 2007;Gavassa et al, 2013). Though male and female G. omarorum display aggression all year round in intrasexual and intersexual interactions, we focused on the non-breeding dyadic agonistic encounters as a remarkable example of non-sex-biased territorial aggression (Batista et al, 2012).…”

Melatonin Regulates Daily Variations in Electric Behavior Arousal in Two Species of Weakly Electric Fish with Different Social Structures

“…Energy expenditure and predator detection risk constrain the EOD [Salazar and Stoddard, 2008]. Given that EOD is a costly signal [Nelson and MacIver, 2006;Salazar and Stoddard, 2008;Gavassa et al, 2013], it is plausible that species with different levels of sociality employ different strategies of energy investment. We predict, for example, that the energy expenditure necessary to sustain the cost of the nocturnal increase is effective mainly in gregarious species that are continually engaged in communication.…”