they will endow her offspring with genes to ensure future survival. Finally,
it is possible that the relationship between signal and receiver properties
might be due to males responding to selection to produce sounds that
females already find appealing.
Acoustic signals have been repeatedly shown to be sexually selected,
most often in birds, insects, and frogs, but also in fish and mammals
(Andersson 1994). Andersson (1994) reviews a number of cases of sexually
selected acoustic signals in all of these taxa. Across taxa, we often find that
females prefer to mate with males that produce louder, longer, more rapidly
produced calls (reviewed in Ryan and Keddy-Hector 1992). As noted
above, such preferences could lead to matings with physically or genetically
superior males and thus be directly or indirectly selected, or the preferences
could result from the increased detectability of such signals or from
females’ preexisting biases toward certain types of signals. In Section 6, we
discuss further the evolution of female mating preferences for male traits.
5.2.1. Neuroethological Mechanisms of Sexual Selection
Neuroethology has not played as crucial a role in explaining the behavioral
mechanisms that contribute to sexual selection as it has in elucidating the
role of behavioral isolating mechanisms in speciation. In some ways, the
successes of neuroethology in identifying species-specific decoding mechanisms might have constrained it from similar success in sexual selection. In
both speciation and sexual selection, it is crucial to understand how neural
mechanisms allow the receiver to sieve through substantial signal variation
to identify biologically meaningful signals. But the focus of the variation,
and thus the focus of researchers, can be quite different in the two types
of studies. In trying to understand species recognition, receivers and
researchers alike confront the variation among species. Given signal variation at this level, how can the receiver identify a conspecific signal? In
sexual selection, however, it is the variation within the species that is crucial,
and one must ask how and why receivers are guided to one rather than
another conspecific variant. This is not the type of question that neuroethologists originally set out to address about communication.
6. Signal–Receiver Coevolution
We have been discussing a variety of factors that cause and constrain the
evolution of long-distance signals. But communication is a dyadic interaction, and signal evolution will proceed only if changes in the signal are
meaningful to the receiver. This problem has been a major focus of
interest in both speciation and sexual-selection studies. In the former, it is
necessary to understand not only how mate-recognition signals evolve
among incipient species but how the receivers evolve at the same time and
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M.J. Ryan and N.M. Kime
it is possible that the relationship between signal and receiver properties
might be due to males responding to selection to produce sounds that
females already find appealing.
Acoustic signals have been repeatedly shown to be sexually selected,
most often in birds, insects, and frogs, but also in fish and mammals
(Andersson 1994). Andersson (1994) reviews a number of cases of sexually
selected acoustic signals in all of these taxa. Across taxa, we often find that
females prefer to mate with males that produce louder, longer, more rapidly
produced calls (reviewed in Ryan and Keddy-Hector 1992). As noted
above, such preferences could lead to matings with physically or genetically
superior males and thus be directly or indirectly selected, or the preferences
could result from the increased detectability of such signals or from
females’ preexisting biases toward certain types of signals. In Section 6, we
discuss further the evolution of female mating preferences for male traits.
5.2.1. Neuroethological Mechanisms of Sexual Selection
Neuroethology has not played as crucial a role in explaining the behavioral
mechanisms that contribute to sexual selection as it has in elucidating the
role of behavioral isolating mechanisms in speciation. In some ways, the
successes of neuroethology in identifying species-specific decoding mechanisms might have constrained it from similar success in sexual selection. In
both speciation and sexual selection, it is crucial to understand how neural
mechanisms allow the receiver to sieve through substantial signal variation
to identify biologically meaningful signals. But the focus of the variation,
and thus the focus of researchers, can be quite different in the two types
of studies. In trying to understand species recognition, receivers and
researchers alike confront the variation among species. Given signal variation at this level, how can the receiver identify a conspecific signal? In
sexual selection, however, it is the variation within the species that is crucial,
and one must ask how and why receivers are guided to one rather than
another conspecific variant. This is not the type of question that neuroethologists originally set out to address about communication.
6. Signal–Receiver Coevolution
We have been discussing a variety of factors that cause and constrain the
evolution of long-distance signals. But communication is a dyadic interaction, and signal evolution will proceed only if changes in the signal are
meaningful to the receiver. This problem has been a major focus of
interest in both speciation and sexual-selection studies. In the former, it is
necessary to understand not only how mate-recognition signals evolve
among incipient species but how the receivers evolve at the same time and
246
M.J. Ryan and N.M. Kime