Preferences based on spectral differences in acoustic signals in four species of treefrogs (Anura: Hylidae)

Abstract

Animals with sensory specializations have been favorite subjects for research in both evolutionary biology and neurobiology. The advantage for evolutionary studies is that intraspecific communication may then depend on a relatively circumscribed set of signal properties of a single sensory modality. Research concerned with mate choice, for example, can thus focus on variation in signals and preferences that are necessarily under strong selective pressure. For the neurobiologist, sensory specializations facilitate the search for functionally important neurons and networks that are likely to be over-represented in the sensory system (e.g. overrepresentation of echo-location call frequencies in the peripheral auditory system of bats, interaural time-sensitive neurons in barn owls, and texture-sensitive tactile neurons in star-nosed moles) (Koppl et al., 1993;Catania and Henry, 2006; Suga, 1979). In this study, the peripheral specialization of the auditory system of frogs sets up a straightforward test of broad interpretations of the matched-filter and pre-existing bias hypotheses.Frogs and toads have served as important model systems for the study of both evolution and mechanisms of auditory processing because of their strong reliance on acoustic communication (for a review, see Gerhardt and Huber, 2002). Their auditory system is specialized at the peripheral level by virtue of having two inner ear organs with different frequency sensitivities and physiological properties (for a review, see Feng and Schellart, 1999). Capranica (Capranica, 1965;Capranica and Moffat, 1983) pointed out the correspondence of the tuning of these two organs with the frequency bands emphasized in the conspecific advertisement call of several species of anurans and popularized the matched-filter hypothesis. Under this hypothesis, the auditory system is maximally sensitive to frequencies strongly represented in conspecific calls and less sensitive to (filters out) the signals of other species and abiotic noise, which are expected to differ in their spectral content from conspecific signals. A matched-filter system would therefore facilitate communication and signal recognition in noisy environments. Comparative studies have confirmed Capranica's expectation of auditory tuning to conspecific-call frequencies in Frogs have two inner ear organs, each tuned to a different range of frequencies. Female treefrogs (Hylidae) of three species in which males produce calls with a bimodal spectrum (Hyla chrysoscelis, H. versicolor, H. arenicolor) preferred alternatives with a bimodal spectrum to alternatives with a single high-frequency peak. By contrast, females of H. avivoca, in which males produce calls with a single, high-frequency peak, preferred synthetic calls with a single high-frequency peak to calls with a bimodal spectrum. These results are consistent with the expectations of the matched-filter hypothesis and run counter to the predictions of the pre-existing bias hypothesis. At moderate to high playback levels (85-90·dB), females of H. aviv...

Sex differences and endocrine regulation of auditory-evoked, neural responses in African clawed frogs (Xenopus)

“…In other frog species with a 2:1 call frequency ratio, there are minimal sex differences in auditory tuning (Schrode et al 2014). In frogs that produce calls made up of only one frequency, adding tones to create 2:1 ratios (as well as other ratios used by Xenopus ) had no effect on female preference (Gerhardt et al 1990; Witte et al 2001; Gerhardt et al 2007; Gerhardt and Humfeld 2013), suggesting that some frogs are more tuned to frequency than frequency ratio for behavioral decision making.…”

Calling site choice and its impact on call degradation and call attractiveness in the gray treefrog, Hyla versicolor

“…Each pulse has spectral peaks (and relative amplitudes) at, on average, about 1.1 kHz (−6 dB) and 2.2 kHz (0 dB), and frequency varies among males of different size (Gerhardt 1991(Gerhardt , 2005a. However, call preferences of females based on frequency differences are fairly weak (Gerhardt 2005a), and our New York animals exhibit no discrimination among calls lacking energy in different spectral bands (Gerhardt et al 2007). Call recognition (and species discrimination) by females of H. versicolor is primarily mediated by the durations of pulses and interpulse intervals and to a lesser degree by pulse shape .…”

“…The null hypothesis of no preference was evaluated with two-tailed binomial tests. For each test result, we also provide the Bayesian central confidence interval (i.e., credible interval; see Gerhardt et al 2007). For the single speaker tests, we used the two significance criteria of Schul and Bush (2002).…”

Vibrational playback by means of airborne stimuli

“…We considered compensation successful if the frequency- response of the plant stem was, on average, within ±3dB across the sampled range, which is the standard criterion in acoustic studies (e.g. Gerhardt et al, 2007).…”