Abstract
Divergence of acoustic signals in a geographic scale results from diverse evolutionary forces acting in parallel and affecting directly inter-male vocal interactions among disjunct populations. Pleurodema thaul is a frog having an extensive latitudinal distribution in Chile along which males' advertisement calls exhibit an important variation. Using the playback paradigm we studied the evoked vocal responses of males of three populations of P. thaul in Chile, from northern, central and southern distribution. In each population, males were stimulated with standard synthetic calls having the acoustic structure of local and foreign populations. Males of both northern and central populations displayed strong vocal responses when were confronted with the synthetic call of their own populations, giving weaker responses to the call of the southern population. The southern population gave stronger responses to calls of the northern population than to the local call. Furthermore, males in all populations were stimulated with synthetic calls for which the dominant frequency, pulse rate and modulation depth were varied parametrically. Individuals from the northern and central populations gave lower responses to a synthetic call devoid of amplitude modulation relative to stimuli containing modulation depths between 30–100%, whereas the southern population responded similarly to all stimuli in this series. Geographic variation in the evoked vocal responses of males of P. thaul underlines the importance of inter-male interactions in driving the divergence of the acoustic traits and contributes evidence for a role of intra-sexual selection in the evolution of the sound communication system of this anuran.
Highlights
Animal communication signals convey information from senders to receivers contributing prezygotic barriers, promoting by these means reproductive isolation [1] and speciation [2]
A first goal of the current study is to investigate the role of intrasexual selection as an evolutionary force that in addition to genetic drift may explain the divergence of advertisement calls of P. thaul along its wide geographical distribution
Multiple regressions showed no dependence of the evoked vocal responses (EVRs) variables measured (NP, DP, off ratio (OR) and dominant frequency (DF)) on temperatures or body dimensions (p.0.05), with the only exception of a positive relationship between body weight and pulse duration in Los Maitenes (Multiple regression: F4,9 = 4.3393, p = 0.0448)
Summary
Animal communication signals convey information from senders to receivers contributing prezygotic barriers, promoting by these means reproductive isolation [1] and speciation [2]. Signals have been shown to exhibit important intraspecific variation related to geographical distribution. Such differences among populations have been related to environmental factors [3][4][5] and to evolutionary divergence [2][6][7][8][9]. The study of mate choice has received considerable attention from behavioral biologists and its importance for the evolution of communication signals has been extensively acknowledged. These efforts have encompassed studies on the influence of geographic variation of signals on female preferences [18][19][20] and on signal evolution [21][22][23]. In contrast with studies focusing on the relevance of signal variation for female behavior, the significance of geographic variation of vocalizations for signal recognition among vocal-interacting males has received limited attention
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