Understanding the sources and magnitudes of variation in signal traits is an important first step towards understanding the forces that may act on signal evolution. In anuran amphibians, acoustic communication plays a major role in the processes of mate attraction and aggression. The significance of variation in characteristics of the mate-attracting advertisement calls is relatively well understood, whereas another call type, the aggressive call, has received much less attention. I recorded both advertisement and aggressive calls given by male grey treefrogs, Hyla versicolor, in staged competitive interactions. From these recordings, I assessed the effects of physical and abiotic influences on signal production by measuring the correlations between the call characteristics of both call types and variables associated with size, body condition and body temperature. I also estimated within- and between-male variation in call characteristics. Temperature affected diverse characteristics of both call types, whereas the effects of morphology were limited primarily to call-frequency variables. Spectral characteristics of both call types were largely static within males, whereas gross-temporal characteristics were much more variable. Within each call type, many of the call characteristics were correlated with one another, whereas between call types, there were relatively few strong correlations between call characteristics. I discuss these results in terms of their implications for signal evolution, mate choice and assessment in contests.
Taxonomic descriptions of new anuran species are published with high frequency in the recent systematics literature. In contrast, there are fewer detailed quantitative descriptions of the vocalizations of these new species. Here, we describe the vocalizations of a recently described shrub frog, Pseudophilautus kani (Anura: Rhacophoridae; Biju and Bossuyt 2009) endemic to the Western Ghats region of India. We recorded two distinct, pulsatile call types that could be distinguished by their temporal and spectral properties as well as their mode of production. Type 1 calls (creek) were short ( ≈ 85 ms), consisted of about six or seven pulses (92 pulses/s) and had a spectrum with a single frequency peak at about 3.5 kHz. By comparison, Type 2 calls (ta-ta-ta-ta) were typically longer ( ≈ 320 ms), contained fewer pulses (4–5) produced at much lower rates (12 pulses/s) and had broadband spectra with multiple frequency peaks, two of which were consistently present at about 2.3 and 4.6 kHz. Video analyses indicated that males produced pulses in Type 1 calls using a single, continuous contraction of the trunk musculature, whereas pulses of Type 2 calls were produced with separate muscle contractions. In both call types, spectral properties were significantly negatively related with body length and body mass. The pulse rate and pulse period of Type 2 calls were also related to body size. No call properties were correlated with body condition. Patterns of individual variation in call properties were generally consistent with those described for other anurans.
India is one of the 12 mega diversity countries of the world due to high endemism. Rajasthan is the largest State of India and its major part is covered by the desert popularly known as the Thar desert. Anuran species are unique in this region but are facing problems due to extension of desert ranges, climate changes and habitat destruction. Out of the 225 species of anurans found in India, 12 species represented by four families namely Bufonidae ( Duttaphrynus melanostictus B. stomaticus, B. viridis),Ranidae (Euphlyctis cyanophlyctis E. hexadactylus Hoplobatrachus tigerinus F. limnocharis Sphaerotheca breviceps S. rolandae), Microhylidae (Microhyla ornata and Uperodon systoma) and Rhacophoridae (Polypedates maculates) have been reported by the author from Rajasthan. Very little attention has been paid for the identification of anurans on the basis of their calls from this region. Among these Bufonids and Microhylids are characterized by one vocal sacs, two in the Ranids but indistinct externally in the P. maculates. The spectrum generated using Raven Pro show very distinct call and pulse patterns in all these anurans. The highest Frequency ranges from 3.5 to 9.5 kHz in these species. In most cases dominant frequency is observed at low frequency ranges. In a call group, most Ranids show distinct inter call intervals but in the Bufonids such intervals are not distinct. Inter pulse interval is also very distinct in different species. The spectral pattern of these specie is so distinct that this can be used for identification, classification (sono-taxonomy) and monitoring of their population even in the desert habitats.
Recent and important studies have pointed out that environmental stress can represent a factor of strong risk for amphibian populations in Europe and, in particular, for the Italian complex of water frogs Rana (Pelophylax) lessonae. The analysis of vocalization in a single species can be an useful cognitive tool to better understand his behaviour and an interesting start point for conservation strategies. In the last twenty years, an increasing amount of attention has been dedicated to study of vocalization of European water frogs populations (Rana ridibunda, R. lessonae and their viable, fertile hybrid R. esculenta), in order to provide additional tool of biogeographic survey, and to underline the similarities and differences among several populations. Only one study has attempted to discuss the taxonomic question of the species that living in Central Italy using a bioacoustic approach, in synergy with other techniques. In our work, we want to provide a methodological contribution for the bioacoustic characterization of the green frog populations, through a sampling protocol and a connected technical analysis. Two green frog populations were investigated and more than 3200 calls in the field, during three breeding seasons, are recorded. The acoustic records have been performed in two sites with different environmental features and with a comparable number of male specimens. The results of this analysis has allowed to highlight the inter and intra-population differences. Furthermore, we provide a description of the individual sequences of vocalizations, spectral and temporal features of mating and territorial calls.
Fixed site attachment and a long calling period within an environment of little temperature change render the males of the diurnal Pan-Amazonian frog Allobates femoralis a rewarding species for field studies on both calling and hearing in anurans. The terrestrial calling positions are spaced at several meters, thus allowing to move within the territories without disturbing the resident males. Vocally active males react with stereotypic phonotactic responses to the playback of conspecific and a large variety of synthetic calls. To test for interference effects of co-occurring species on the male-male communication system of A. femoralis, we compared the calls and the phonotactic reaction of territorial males at eight Amazonian sites: four where A. femoralis occurs together with Ameerega trivittata and four where A. trivittata is absent. The occurrence of A. trivittata apparently gave rise to narrower and asymmetric frequency-response curves in A. femoralis, without concomitant differences in the call or in body size. Playback experiments have also allowed to disentangle the relative contribution of visual and auditory cues in multimodal signalling. To investigate the relative contributions of different evolutionary mechanisms to geographic differentiation of these populations, we compared calls, colouration, body shape, and the cyt-b gene. The studied traits did not evolve as a unit. Against our expectations and in contrast to current models of speciation in the Amazon basin, a significant amount of geographic variation in calls and cyt-b was attributable to geographic distance between populations. To the best of our knowledge, up to now A. femoralis has been among the most intensively studied anuran species under completely natural conditions, i.e. without touching the frogs prior to and during the acoustic field experiments.
The study of auditory illusions has been important in elucidating the rules of auditory grouping in humans, which adhere to principles first described by Gestalt psychologists to explain the formation of visual objects. For example, the human auditory system perceptually restores short, deleted segments of speech and other sounds (e.g., tones) when the resulting silent gaps are filled by a potential masking noise. This “temporal induction” of missing sounds accounts for phenomena such as “phonemic restoration” of speech and the so-called “continuity illusion”. Results from studies of such illusions suggest that the Gestalt principle of “continuity” allows humans to perceive complete auditory objects in the face of incomplete or degraded acoustic information in the presence of noise. Although similar findings have been reported in two nonhuman primates and one songbird, the general relevance of such illusory percepts in acoustic communication across a wide range of taxa remains unknown. The present study tested the hypothesis that female treefrogs experience the illusory perceptual restoration of discrete pulses in the male sexual advertisement signal when they are deleted and replaced by a potential masking noise. While added noise restored some attractiveness to degraded signals, there was no evidence that the frogs experienced the illusion of perceiving actual pulses that were missing. Instead, the added noise appeared to function as an acoustic ornament that made some signals more attractive than others as a result of an inherent sensory bias for greater sensory stimulation. Whether such sensory biases themselves adhere to Gestalt principles of auditory grouping remains to be demonstrated.
Vocal activity in ectothermal animals such as anurans is closely linked to environmental temperatures. Therefore, this activity can be used to measure the response of the animal to thermal changes in the ecosystems within the context of climate change. We monitored environmental temperature during vocal activity of several Iberian treefrog populations of the genus Hyla under very different climatic cycles. A comparison of the selected call temperatures between population and species level will be presented like an index of these species to adapt to the thermal changes in the ecosystems. In the Iberian Peninsula Hyla arborea and Hyla meridionalis have large distributions, including habitats with very diverse thermal and meteorological conditions. For each species, a population from the hot thermal extreme and an one from the cold extreme of the species range were monitored by new automated recording systems for three years. Call detection from the automated recordings was completed using both sound spectrogram correlation (Xbat, Cornell Lab) and algorithm-based Markov chains (Song Scope, Wildlife Acoustics). Here we discuss the preliminary results and their biological significance. The selection of different call temperatures observed within population and between species level show some degree of plasticity apparently associated to environmental thermal conditions. Thus, this plasticity could affect the response of these species to the climatic warming. In fact, recent distribution data indicate a process of expansion in these two species in Iberia. The comparison of our results with other species will help to assess the phylogenetic weight in this phenomenon.
For two consecutive seasons or more we monitored the vocal activity of populations located at thermal extremes of the distribution in the Iberian Peninsula of three species of midwife toads. We used automated recording stations with a fixed time-based recording protocol (3 min per hour, 24 hrs per day), coupled with dataloggers measuring water, soil and air temperature as well as air relative humidity. The correlation between body size and call dominant frequency allows to infer information about the distribution of male body size (age) in the chorus. Calling activity was detected in the digital files using X-Bat software. The phenology of vocal activity varies greatly between sites and species both in date of initiation and in duration of calling season. Chorus attendance and composition (size distribution) varies with time within population and also between populations. The results confirm the value of acoustic monitoring as a valid methodology for census and demographic comparisons of populations. The results about thermal correlation of calling conditions show a moderate amount of within-species variability and more marked between-species differences.
Mate-attracting signals are made up of different properties that influence mating decisions. Analysis of patterns of variation in such properties and patterns of female preference based on such variation can reveal the potential for sexual selection and speciation. I will discuss patterns of variation in four such properties at three levels -within-male, between-male, and between-population - in 35 populations of the North American treefrog (Hyla chrysoscelis). Three properties (pulse number, dominant frequency and pulse rate) show patterns of variation that would allow selection on individual males, and pulse number is under directional selection by females. However, the pattern of selection is non-linear (diminishing returns of adding pulses over and above the mean) and also constrained by energetic costs. Surprisingly, only pulse rate, which is under strong stabilizing selection within populations, shows between-population differentiation sufficient to promote discrimination by females. The pattern of geographical variation in pulse rate is not explained by reproductive character displacement, which predicts a higher pulse rate in areas where a genetically incompatible sibling species is found, but females do show such a pattern in the strength of preferences based on pulse rate. By contrast, pulse rate in the sibling species (H. versicolor), which has arisen three or more times by polyploid speciation, varies little among populations. I will show that part of the explanation is that lower pulse rates are a consequence of cell-size increases that accompany genome duplication. I also propose that two changes in the female-preference criteria of the polyploid species are examples of hidden preferences revealed by changes in male calls.
The calls of Pipa carvalhoi were recorded with a hydrophone and analysed with a sound level meter, and the data compared with those measured in air. Three types of calls can be differentiated in males (females are not able to produce calls):
the advertisement call which is composed of clicks followed by a series of rapid identical pulses; this series, called buzz by Weygoldt (1976), is named trill here;
the encounter call consisting of short trills, and
a call which is very similar to the encounter call, but preceded occasionally by clicks. It is produced by males in response to amplexus.
The sound pressure level of trills reached 120 dB, that of clicks 90 dB. Corresponding data for the sound measured in air are 62 and 41 dB. Experiments with wall covers suppressing resections suggest that the high dB values measured in normal aquaria are unbiased. Calling activity is high at midnight and in the morning; it increases in the presence of receptive females. In a group, the dominant male calls; however, when a female becomes receptive, other males produce encounter calls.
