roaring rate is an honest signal of fighting ability because both are dependent on bodily condition and stamina. Clutton-Brock and Albon (1979) suggested that this results from the fact that the same thoracic musculature is
used for fighting and roaring but commented that “current knowledge of
cervid physiology is inadequate” to evaluate that hypothesis. Unfortunately,
this comment is still mostly true twenty years later, although recent work
has revealed some interesting adaptations for sound production in red deer
(Fitch and Reby 2001; see below). Resolution of such questions demands
an understanding of the mechanisms used to produce sound and their physiological and anatomical relationship to other systems. Considerations such
as these have led to an increased interest in production mechanisms in
recent years and to a growing consensus that our understanding of the evolution of acoustic signaling systems will remain incomplete until the physics
and physiology of signal production are better understood (Hauser 1996;
Krebs and Davies 1997; Bradbury and Vehrencamp 1998).
In this chapter, we will address the production of acoustic signals from a
dynamic evolutionary perspective, paying close attention to the role of
physical and phylogenetic constraints on the evolution of acoustic signals
and the mechanisms that produce them. This choice of perspective is somewhat atypical and perhaps requires justification. First, why focus on signalproduction mechanisms? For researchers in the behavioral ecology
tradition, who typically seek ultimate evolutionary explanations for a given
pattern of behavior, the proximate mechanisms responsible for a behavior
have often appeared irrelevant. However, researchers in evolutionary
bioacoustics can expect at least two benefits from a basic knowledge of
sound-production mechanisms. First, our ability to conduct research in bioacoustics depends crucially on our ability to analyze animal sounds precisely
and in some cases to synthesize them, both of which hinge critically on a
solid understanding of the acoustic mechanisms that generate them.
Second, an understanding of mechanism offers crucial insights into the
adaptive landscape of a communication system: what sounds are easy or
impossible to produce? What are the costs and benefits of a given sound
type in terms of energetics, predator detection, environmental transmission,
and receiver characteristics? What are the possibilities, for a given species,
to cheaply produce honest signals or to cheaply mimic honest signals? The
data we will review below indicate that the laws of physics, and the structure of sound-producing organs, place strong constraints on the possible
evolution of acoustic signals, determining what information is available for
perceivers to exploit initially, what deceptive or skeptical mutations can
subsequently arise, and the costs and benefits of producing and responding
to a given signal. Far from being a wide open field, the adaptive landscape
for vertebrate acoustics seems to be characterized by a circumscribed range
of biologically relevant and potentially honest signals and an even narrower
range of potentially deceptive mechanisms (both morphological and behavioral). Thus, we argue, an understanding of signal-production mechanisms
3. Unpacking “Honesty”
67
used for fighting and roaring but commented that “current knowledge of
cervid physiology is inadequate” to evaluate that hypothesis. Unfortunately,
this comment is still mostly true twenty years later, although recent work
has revealed some interesting adaptations for sound production in red deer
(Fitch and Reby 2001; see below). Resolution of such questions demands
an understanding of the mechanisms used to produce sound and their physiological and anatomical relationship to other systems. Considerations such
as these have led to an increased interest in production mechanisms in
recent years and to a growing consensus that our understanding of the evolution of acoustic signaling systems will remain incomplete until the physics
and physiology of signal production are better understood (Hauser 1996;
Krebs and Davies 1997; Bradbury and Vehrencamp 1998).
In this chapter, we will address the production of acoustic signals from a
dynamic evolutionary perspective, paying close attention to the role of
physical and phylogenetic constraints on the evolution of acoustic signals
and the mechanisms that produce them. This choice of perspective is somewhat atypical and perhaps requires justification. First, why focus on signalproduction mechanisms? For researchers in the behavioral ecology
tradition, who typically seek ultimate evolutionary explanations for a given
pattern of behavior, the proximate mechanisms responsible for a behavior
have often appeared irrelevant. However, researchers in evolutionary
bioacoustics can expect at least two benefits from a basic knowledge of
sound-production mechanisms. First, our ability to conduct research in bioacoustics depends crucially on our ability to analyze animal sounds precisely
and in some cases to synthesize them, both of which hinge critically on a
solid understanding of the acoustic mechanisms that generate them.
Second, an understanding of mechanism offers crucial insights into the
adaptive landscape of a communication system: what sounds are easy or
impossible to produce? What are the costs and benefits of a given sound
type in terms of energetics, predator detection, environmental transmission,
and receiver characteristics? What are the possibilities, for a given species,
to cheaply produce honest signals or to cheaply mimic honest signals? The
data we will review below indicate that the laws of physics, and the structure of sound-producing organs, place strong constraints on the possible
evolution of acoustic signals, determining what information is available for
perceivers to exploit initially, what deceptive or skeptical mutations can
subsequently arise, and the costs and benefits of producing and responding
to a given signal. Far from being a wide open field, the adaptive landscape
for vertebrate acoustics seems to be characterized by a circumscribed range
of biologically relevant and potentially honest signals and an even narrower
range of potentially deceptive mechanisms (both morphological and behavioral). Thus, we argue, an understanding of signal-production mechanisms
3. Unpacking “Honesty”
67