Male vocal competition is dynamic and strongly affected by social contexts in music frogs

Abstract

Male-male vocal competition in anuran species is critical for mating success; however, it is also highly time-consuming, energetically demanding and likely to increase predation risks. Thus, we hypothesized that changes in the social context would cause male vocal competition to change in real time in order to minimize the costs and maximize the benefits of competition. To test this hypothesis, we assessed the effect of repeating playbacks of either white noise (WN) or male advertisement calls on male call production in the Emei music frog (Babina daunchina), a species in which males build mud-retuse burrows and call from within these nests. Previous studies have shown that calls produced from inside burrows are highly sexually attractive (HSA) to females while those produced outside nests are of low sexual attractiveness (LSA). Results showed that most subjects called responsively after the end of WN playbacks but before the onset of conspecific call stimuli although call numbers were similar, indicating that while males adjusted competitive patterns according to the biological significance of signals, their competitive motivation did not change. Furthermore, these data indicate that the frogs had evolved the ability of interval timing. Moreover, when the inter-stimulus interval (ISI) between playbacks was varied, the subjects preferentially competed with HSA calls when the ISI was short (\4 s) but responded equally to HSA and LSA calls if the ISI was long (C4 s), suggesting that males allocate competitive efforts depending on both the perceived sexual attractiveness of rivals and the time available for calling. Notably, approximately two-thirds of male calls occurred in response to HSA calls, a preference rate comparable to that previously found for females in phonotaxis experiments and consistent with the idea that the mechanisms underlying both the male's competitive responses to rivals and the female's preferences toward potential mates coevolved under the same selective pressure.

Right ear advantage for vocal communication in frogs results from both structural asymmetry and attention modulation

“…Since both male signaling and female choice are dynamic processes in anurans [33,34], acoustic signal processing could be reflected by the dynamic properties of the EEG recorded from the well-organized auditory mesencephalon rather than from the more dispersed neural networks of the auditory telencephalon. Therefore, the fact that the dynamic changes within specific EEG bands over time presented solely in the left mesencephalon but not on either side of the telencephalon probably reflect the existence of structural asymmetries in the auditory midbrain which play a key role in anuran vocal communication and bring about the REA observed in this species.…”

“…Thus, a left-hemisphere/right-ear processing advantage for communication sounds in anurans may be mediated by brainstem pathways providing a preferred channel derived from the right ear to the left midbrain and telencephalon. Since both male signaling and female choice are dynamic processes in anurans [33,34], unfolding in real time, REA and its underlying mechanisms would also be expected to estimate by varying dynamically correlated EEG activity in the left hemisphere, especially in the auditory midbrain which is closely associated with the ascending auditory input.…”

Electroencephalographic signals synchronize with behaviors and are sexually dimorphic during the light–dark cycle in reproductive frogs

“…injections of gonadotropin-releasing hormone (gnrH-A6; Sichuan, China; 1.25 μg per animal). After 24 h, the reproductive status of females was determined based on phonotaxis behavior (i.e., approaching a speaker broadcasting male advertisement calls) and that of males was determined by recording call activity as described previously (Cui et al 2011b;Fang et al 2012bFang et al , 2013. Accordingly, neurophysiological and behavioral recordings began 24 h after the hormone injections, and continued for 24 h, mindful of the fact that the induced reproductive behaviors could continue for 3 days or more.…”

The biological significance of acoustic stimuli determines ear preference in the music frog

“…Babina males produce advertisement calls from within hidden burrows whose resonant properties alter the acoustic properties of the calls Cui et al, 2012Cui et al, , 2010. Phonotaxis experiments have shown that 70% of female Babina prefer calls produced from within the burrows, which are hence more highly sexually attractive (HSA) than those produced from outside the burrows, which are less sexually attractive (LSA) and the male Babina prefer competing vocally with HSA calls rather than with LSA calls (Fang et al, 2014a). Electrophysiological studies show that relative power in the alpha, delta and beta bands declines or increases with time in the left but not right mesencephalon, with the most notable changes occurring during playbacks of HSA calls (Fang et al, 2014b).…”

“…Thus, the population level rather than the individual level of lateralization was measured in the present study. As previous EEG studies have shown that conspecific calls most strongly activate the left hemisphere of animals with REA, we predicted that music frogs would turn generally rightwards in order to improve discrimination when hearing conspecific calls, with a stronger preference for HSA than LSA calls Fang et al, 2014a). For other acoustic stimuli, we also predicted that (1) stimuli novel to frogs such as white noise (WN) would elicit either no turning or no orientation preference, and stimuli related to (2) explosive environmental sounds such as thunder or (3) sounds associated with predation would evoke either left turn movement or little preference, as reported in dogs (Reinholz-Trojan et al, 2012;Siniscalchi et al, 2008).…”