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Animal choruses emerge from receiver psychology

View Article: PubMed Central - PubMed

ABSTRACT

Synchrony and alternation in large animal choruses are often viewed as adaptations by which cooperating males increase their attractiveness to females or evade predators. Alternatively, these seemingly composed productions may simply emerge by default from the receiver psychology of mate choice. This second, emergent property hypothesis has been inferred from findings that females in various acoustic species ignore male calls that follow a neighbor’s by a brief interval, that males often adjust the timing of their call rhythm and reduce the incidence of ineffective, following calls, and from simulations modeling the collective outcome of male adjustments. However, the purported connection between male song timing and female preference has never been tested experimentally, and the emergent property hypothesis has remained speculative. Studying a distinctive katydid species genetically structured as isolated populations, we conducted a comparative phylogenetic analysis of the correlation between male call timing and female preference. We report that across 17 sampled populations male adjustments match the interval over which females prefer leading calls; moreover, this correlation holds after correction for phylogenetic signal. Our study is the first demonstration that male adjustments coevolved with female preferences and thereby confirms the critical link in the emergent property model of chorus evolution.

No MeSH data available.


Inhibitory-resetting model for signal interactions between male neighbors in rhythmic acoustic species.Black sawtooth line in upper trace shows the periodic ascent (rb, rebound) and descent of the free-running central rhythm generator. After an effector delay t following ascent to the peak level, a call (thick blue dash) is broadcast; meanwhile the generator descends to its basal level over interval r. Calls are repeated rhythmically with a period T. Lower trace shows the same central rhythm generator as it is repeatedly inhibited and reset by a stimulus (male neighbor or acoustic playback; thick red dash). T′ is the modified call period following a stimulus. The rebound rb from inhibition following a stimulus steepens when the stimulus occurs after a longer post-call delay d; rb is steepest (rb3) when the stimulus occurs just as the rhythm generator has ascended to its peak level (following post-call delay d3), yielding the shortest post-stimulus delay for the focal male’s next call. This minimum post-stimulus call delay is designated m. The model is adapted from ref. 21 and was derived from results in extensive playback experiments with various species, including E. diurnus.
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f1: Inhibitory-resetting model for signal interactions between male neighbors in rhythmic acoustic species.Black sawtooth line in upper trace shows the periodic ascent (rb, rebound) and descent of the free-running central rhythm generator. After an effector delay t following ascent to the peak level, a call (thick blue dash) is broadcast; meanwhile the generator descends to its basal level over interval r. Calls are repeated rhythmically with a period T. Lower trace shows the same central rhythm generator as it is repeatedly inhibited and reset by a stimulus (male neighbor or acoustic playback; thick red dash). T′ is the modified call period following a stimulus. The rebound rb from inhibition following a stimulus steepens when the stimulus occurs after a longer post-call delay d; rb is steepest (rb3) when the stimulus occurs just as the rhythm generator has ascended to its peak level (following post-call delay d3), yielding the shortest post-stimulus delay for the focal male’s next call. This minimum post-stimulus call delay is designated m. The model is adapted from ref. 21 and was derived from results in extensive playback experiments with various species, including E. diurnus.

Mentions: An alternative to the adaptationist paradigm above, and a key to its thorough examination, is the hypothesis that the collective singing patterns in choruses, so conspicuous to human observers, simply emerge from the ‘receiver psychology’16 of female perception and preference101517. For want of explicit experiments conducted on appropriate chorusing species, the hypothesis has been especially conjectural. But recent neuroethological studies of female preference point toward a specific 3-step pathway along which basic perception and sexual selection could ultimately lead to chorusing: In various acoustic species females prefer male calls that precede a neighbor’s call by a brief interval18, a variant of the precedence effects known from psychoacoustic research19. The next step in the pathway is the finding in many species which sing rhythmically that when a male hears a song stimulus, he delays his subsequent call via a mechanism involving momentary inhibition of his central rhythm generator and resetting of his phase relative to that stimulus910 (Fig. 1). Finally, when multiple males use equivalent mechanisms an expansive chorus comprised of synchrony and/or alternation may arise20 (Supplementary note S1). These collective outcomes are predicted by Monte Carlo simulation, and they are consistent with observations of synchrony and alternation in various acoustic insects and anurans21 (Fig. 2). Importantly, the display can be generated in the absence of any selection expressly favoring synchrony or alternation.


Animal choruses emerge from receiver psychology
Inhibitory-resetting model for signal interactions between male neighbors in rhythmic acoustic species.Black sawtooth line in upper trace shows the periodic ascent (rb, rebound) and descent of the free-running central rhythm generator. After an effector delay t following ascent to the peak level, a call (thick blue dash) is broadcast; meanwhile the generator descends to its basal level over interval r. Calls are repeated rhythmically with a period T. Lower trace shows the same central rhythm generator as it is repeatedly inhibited and reset by a stimulus (male neighbor or acoustic playback; thick red dash). T′ is the modified call period following a stimulus. The rebound rb from inhibition following a stimulus steepens when the stimulus occurs after a longer post-call delay d; rb is steepest (rb3) when the stimulus occurs just as the rhythm generator has ascended to its peak level (following post-call delay d3), yielding the shortest post-stimulus delay for the focal male’s next call. This minimum post-stimulus call delay is designated m. The model is adapted from ref. 21 and was derived from results in extensive playback experiments with various species, including E. diurnus.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037466&req=5

f1: Inhibitory-resetting model for signal interactions between male neighbors in rhythmic acoustic species.Black sawtooth line in upper trace shows the periodic ascent (rb, rebound) and descent of the free-running central rhythm generator. After an effector delay t following ascent to the peak level, a call (thick blue dash) is broadcast; meanwhile the generator descends to its basal level over interval r. Calls are repeated rhythmically with a period T. Lower trace shows the same central rhythm generator as it is repeatedly inhibited and reset by a stimulus (male neighbor or acoustic playback; thick red dash). T′ is the modified call period following a stimulus. The rebound rb from inhibition following a stimulus steepens when the stimulus occurs after a longer post-call delay d; rb is steepest (rb3) when the stimulus occurs just as the rhythm generator has ascended to its peak level (following post-call delay d3), yielding the shortest post-stimulus delay for the focal male’s next call. This minimum post-stimulus call delay is designated m. The model is adapted from ref. 21 and was derived from results in extensive playback experiments with various species, including E. diurnus.
Mentions: An alternative to the adaptationist paradigm above, and a key to its thorough examination, is the hypothesis that the collective singing patterns in choruses, so conspicuous to human observers, simply emerge from the ‘receiver psychology’16 of female perception and preference101517. For want of explicit experiments conducted on appropriate chorusing species, the hypothesis has been especially conjectural. But recent neuroethological studies of female preference point toward a specific 3-step pathway along which basic perception and sexual selection could ultimately lead to chorusing: In various acoustic species females prefer male calls that precede a neighbor’s call by a brief interval18, a variant of the precedence effects known from psychoacoustic research19. The next step in the pathway is the finding in many species which sing rhythmically that when a male hears a song stimulus, he delays his subsequent call via a mechanism involving momentary inhibition of his central rhythm generator and resetting of his phase relative to that stimulus910 (Fig. 1). Finally, when multiple males use equivalent mechanisms an expansive chorus comprised of synchrony and/or alternation may arise20 (Supplementary note S1). These collective outcomes are predicted by Monte Carlo simulation, and they are consistent with observations of synchrony and alternation in various acoustic insects and anurans21 (Fig. 2). Importantly, the display can be generated in the absence of any selection expressly favoring synchrony or alternation.

View Article: PubMed Central - PubMed

ABSTRACT

Synchrony and alternation in large animal choruses are often viewed as adaptations by which cooperating males increase their attractiveness to females or evade predators. Alternatively, these seemingly composed productions may simply emerge by default from the receiver psychology of mate choice. This second, emergent property hypothesis has been inferred from findings that females in various acoustic species ignore male calls that follow a neighbor’s by a brief interval, that males often adjust the timing of their call rhythm and reduce the incidence of ineffective, following calls, and from simulations modeling the collective outcome of male adjustments. However, the purported connection between male song timing and female preference has never been tested experimentally, and the emergent property hypothesis has remained speculative. Studying a distinctive katydid species genetically structured as isolated populations, we conducted a comparative phylogenetic analysis of the correlation between male call timing and female preference. We report that across 17 sampled populations male adjustments match the interval over which females prefer leading calls; moreover, this correlation holds after correction for phylogenetic signal. Our study is the first demonstration that male adjustments coevolved with female preferences and thereby confirms the critical link in the emergent property model of chorus evolution.

No MeSH data available.