Call degradation in diploid and tetraploid green toads

S Castellano, C Giacoma… - Biological Journal of the …, 2003 - academic.oup.com
Biological Journal of the Linnean Society, 2003academic.oup.com
According to the 'environmental selection'hypothesis, the physical characteristics of
environments influence the evolution of long-range acoustic signals by favouring those
properties that decrease sound attenuation and distortion with distance. Different
environments could favour different acoustic properties and therefore contribute to the intra-
and interspecific variation of calls. In the present paper, we investigate whether this
hypothesis could explain the differences between the advertisement calls of three taxa of …
Abstract
According to the ‘environmental selection’ hypothesis, the physical characteristics of environments influence the evolution of long-range acoustic signals by favouring those properties that decrease sound attenuation and distortion with distance. Different environments could favour different acoustic properties and therefore contribute to the intra- and interspecific variation of calls. In the present paper, we investigate whether this hypothesis could explain the differences between the advertisement calls of three taxa of central-Asian green toads: lowland diploids, highland tetraploids and lowland tetraploids. The pattern of propagation of 12 natural calls (four for each taxon) was analysed in nine localities of Kyrgyzstan and Kazakstan. We broadcast the calls and recorded them along a trasect at distances of 2, 4, 8, 16, and 32 m from the speaker, to estimate sound attenuation and propagation. Attenuation was quantified from the oscillogram (by directly calculating the SPL of calls) and from the power spectrum (by measuring the relative amplitude of the fundamental frequency) , whereas degradation was estimated by cross-correlating spectrograms of the same call at different distances. Results show that: (1) the pattern of sound propagation significantly differs among localities in relation to the different vegetation and environmental noise; (2) in most localities, call attenuation and degradation differ significantly among the three taxa ; (3) such differences are not consistent to those expected under the hypothesis of environmental selection: independent of altitude, lowland tetraploid calls fare worse than both diploid and highland tetraploid calls, whereas diploid and highland tetraploid calls show different patterns of propagation in a few localities only.
Oxford University Press
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