Circadian Rhythm of Calling Behavior in the Emei Music Frog(Babina daunchina) is Associated with Habitat Temperature and Relative Humidity

Generally, the function of vocalizations made by male anurans are to attract females or defend resources. Typically, males vocalize in choruses during one or more periods in a twenty-four-hour cycle, which varies, however, among species. Nevertheless, the causal factors influencing circadian variations of calling patterns in anuran species are not clear. In this study, male chorus vocalizations were monitored in the Emei music frog(Babina daunchina) for 17 consecutive days during the breeding season, while its habitat air temperature and relative humidity in the course of experiments were measured as well. The results revealed that the circadian calling patterns were characterized by two periods of peak vocalization, which were observed from 0500 h to 0700 h and from 1300 h to 2000 h, while the lowest activity period was found from 2100 h to 2200 h. Both calls/h and notes/h were positively correlated with air temperature and negatively with relative humidity. Overall, our data indicate that the Emei music frogs(B. daunchina) could regulate their vocal activities based on the changes of physical micro-environment(e. g., temperature or humidity) to maximize reproductive success.

Male Music Frogs Compete Vocally on the Basis of Temporal Sequence Rather Than Spatial Cues of Rival Calls

Male-male vocal competition in anuran species may be influenced by cues related to the temporal sequence of male calls as well by internal temporal, spectral and spatial ones. Nevertheless, the conditions under which each type of cue is important remain unclear. Since the salience of different cues could be reflected by dynamic properties of male-male competition under certain experimental manipulation, we investigated the effects of repeating playbacks of conspecific calls on male call production in the Emei music frog（Babina daunchina）. In Babina, most males produce calls from nest burrows which modify the spectral features of the cues. Females prefer calls produced from inside burrows which are defined as highly sexually attractive（HSA） while those produced outside burrows as low sexual attractiveness（LSA）. In this study HSA and LSA calls were broadcasted either antiphonally or stereophonically through spatially separated speakers in which the temporal sequence and/or spatial position of the playbacks was either predictable or random. Results showed that most males consistently avoided producing advertisement calls overlapping the playback stimuli and generally produced calls competitively in advance of the playbacks. Furthermore males preferentially competed with the HSA calls when the sequence was predictable but competed equally with HSA and LSA calls if the sequence was random regardless of the availability of spatial cues, implying that males relied more on available sequence cues than spatial ones to remain competitive.

Behavior and Approximate Entropy of Right-eye Lateralization During Predation in the Music Frog

Brain asymmetry for processing visual information is widespread in animals.However,it is still unknown how the complexity of the underlying neural network activities represents this asymmetrical pattern in the brain.In the present study,we investigated this complexity using the approximate entropy(ApEn)protocol for electroencephalogram(EEG)recordings from the forebrain and midbrain while the music frogs(Nidirana daunchina)attacked prey stimulus.The results showed that(1)more significant prey responses were evoked by the prey stimulus presented in the right visual field than that in the left visual field,consistent with the idea that right-eye preferences for predatory behaviors exist in animals including anurans;(2)in general,the ApEn value of the left hemisphere(especially the left mesencephalon)was greatest under various stimulus conditions,suggesting that visual lateralization could be reflected by the dynamics of underlying neural network activities and that the stable left-hemisphere dominance of EEG ApEn may play an important role in maintaining this brain asymmetry.

Coevolution of Male and Female Response Preferences to Sexual Signals in Music Frogs

Male signaling influences both female choice and male-male competition. Although male signaling characteristics and female preferences have been shown to coevolve in many species, few studies have examined whether male signal characteristics and male receiver responses related to male-male competition also coevolve. The present study tested the hypothesis that male and female signal receiver preferences may coevolve in parallel for flogs in the genus Babina by comparing the acoustic structure of male advertisement calls of four closely related and geographically isolated Babina species. Then we assessed the behavioral responses of both male and female B. daunchina （Emei music frog） to male call playbacks from each of the four species. The results support the hypothesis that male and female signal receiver preferences have coevolved in this species. Specifically, both male and female B. daunchina respond strongly to the heterospecific calls of B. hainanensis, suggesting that preexisting biases exist in both females and males. Both male and female individuals showed a slight response to the calls of B. adenopleura while no response was evoked by the calls ofB. lini. The manifestation of similar response profiles in male and female B. daunchina to the calls of the four species support the idea that male and female signal receiver preferences evolved in parallel and that the origin of these receiver biases reflects adaptations dependent on the same neural and cognitive systems in both sexes.

Flexibility as a Strategy for Avoiding Call Overlap in Male Anhui Treefrogs

Male-male vocal competition is critical for mating success in anuran species;however,it remains unknown that how males regulate their competitive strategies dynamically during competition because calling is highly time-consuming,energetically demanding and likely to increase predation risks.Since different parts of calls will encode different information for vocal communication,we hypothesized that competitive strategies of male frogs may be modulated by the temporal and spectral features of different call notes.To test this hypothesis,the natural advertisement calls(OC),its modified versions with the first call note replaced by white noise(WN)or other notes and with the fifth call note replaced by WN,were played back to the Anhui tree frogs(Rhacophorus zhoukaiyae).Results showed that 1)males produced more competitive calls in response to acoustic stimuli compared to their baseline calling during silence;and 2)males emitted more non-overlapping calls compared to overlapping calls in response to the acoustic stimuli.These results are consistent with the idea that males are flexible to acoustic signals and their competition strategies are modulated dynamically by social contexts.

Changes in Electroencephalogram Approximate Entropy Reflect Auditory Processing and Functional Complexity in Frogs

Brain systems engage in what are generally considered to be among the most complex forms of information processing. In the present study, we investigated the functional complexity of anuran auditory processing using the approximate entropy（Ap En） protocol for electroencephalogram（EEG） recordings from the forebrain and midbrain while male and female music frogs（Babina daunchina） listened to acoustic stimuli whose biological significance varied. The stimuli used were synthesized white noise（reflecting a novel signal）, conspecific male advertisement calls with either high or low sexual attractiveness（reflecting sexual selection） and silence（reflecting a baseline）. The results showed that 1） Ap En evoked by conspecific calls exceeded Ap En evoked by synthesized white noise in the left mesencephalon indicating this structure plays a critical role in processing acoustic signals with biological significance; 2） Ap En in the mesencephalon was significantly higher than for the telencephalon, consistent with the fact that the anuran midbrain contains a large well-organized auditory nucleus（torus semicircularis） while the forebrain does not; 3） for females Ap En in the mesencephalon was significantly different than that of males, suggesting that males and females process biological stimuli related to mate choice differently.

Consistency in responses to conspecific advertisement calls with various signal-to-noise ratios in both sexes of the Anhui tree frog

Environmental noise has a significant negative impact on acoustic communication in most situations,as it influences the production,transmis-sion,and reception of acoustic signals.However,how animals respond to conspecific sounds when there is interference from environmental noise,and whether males and females display convergent behavioral responses in the face of noise masking remain poorly understood.In this study,we investigated the effects of conspecific male advertisement calls with different signal-to-noise ratios on male-male competition and female choice in the Anhui tree frog Rhacophorus zhoukaiyae using playback and phonotaxis experiments,respectively.The results showed that(1)female Anhui tree frogs preferentially selected the conspecific calls with higher SNR compared to calls with lower SNR;(2)males preferen-tially responded vocally to the conspecific calls with higher SNR compared to calls with lower SNR;and(3)males'competitive strategies were flexible in the face of noise interference.These results suggest that preferences of both sexes converge in outcome,and that male competitive strategies may depend on predictable female preferences.This study will provide an important basis for further research on decision-making in animals.

Hierarchical auditory perception for species discrimination and individual recognition in the music frog

The ability to discriminate species and recognize individuals is crucial for reproductive success and/or survival in most animals.However,the temporal order and neural localization of these decision-making processes has remained unclear.In this study,event-related potentials(ERPs)were measured in the telencephalon,diencephalon,and mesencephalon of the music frog Nidirana daunchina.These ERPs were elicited by calls from 1 group of heterospecifics(recorded from a sympatric anuran species)and 2 groups of conspecifics that differed in their fundamental frequencies.In terms of the polarity and position within the ERP waveform,auditory ERPs generally consist of 4 main components that link to selective attention(N1),stimulus evaluation(P2),identification(N2),and classification(P3).These occur around 100,200,250,and 300 ms after stimulus onset,respectively.Our results show that the N1 amplitudes differed significantly between the heterospecific and conspecific calls,but not between the 2 groups of conspecific calls that differed in fundamental frequency.On the other hand,the N2 amplitudes were significantly different between the 2 groups of conspecific calls,suggesting that the music frogs discriminated the species first,followed by individual identification,since N1 and N2 relate to selective attention and stimuli identification,respectively.Moreover,the P2 amplitudes evoked in females were significantly greater than those in males,indicating the existence of sexual dimorphism in auditory discrimination.In addition,both the N1 amplitudes in the left diencephalon and the P2 amplitudes in the left telencephalon were greater than in other brain areas,suggesting left hemispheric dominance in auditory perception.Taken together,our results support the hypothesis that species discrimination and identification of individual characteristics are accomplished sequentially,and that auditory perception exhibits differences between sexes and in spatial dominance.