2.3. State Constraints on Representational Systems
Selection processes shape the acoustics of vocal communication signals.
Constraints that result from these pressures are not restricted to the signal
(i.e., input) acoustics but also the organization (i.e., state) of the representational system. In the following section, we consider a number of ways
in which the organization of the representational system is constrained by
both phylogenetic and ontogenetic processes. These constraints include
potential links between motor and sensory representations, learning, and the
relationship between species and subspecies-level recognition behaviors.
2.3.1. Motor-Sensory Linkages
2.3.1.1. Genetic Coupling and Coevolution
Signal production and perception are linked behaviorally (see Section 1;
Fitch and Hauser, Chapter 3; Ryan and Kime, Chapter 5). One possible
explanation for this parity is that the production of a class of sounds and
perception of sounds of the same class are tightly linked within each
individual. Such an arrangement could result from genetic coupling, wherein
the neural mechanisms for production and perception of a signal would
share common elements controlled by the same set of genes (Alexander
1962).Thus, modification of the genetic material would result in concomitant
changes in production and perception. Although the simplicity of this idea
is attractive, there is no guarantee that the changes will be coordinated or
that the modified element will contribute the same change, in the same direction and magnitude, for both modalities. Rather than postulate a single
genetic basis for separate production and perception systems, a more parsimonious solution is to postulate a single central pattern generator responsible for both production and perception (Bentley and Hoy 1972; Hoy et al.
1977). The predicted role of central pattern generators in perception represents an additional prediction of the genetic-coupling hypothesis.
Alternatively, the match between perception and production could result
from coevolution (von Helversen and von Helversen 1994). By this account,
the mechanisms of production and perception of communication signals are
genetically independent but evolve under reciprocal selective pressure
toward representation of a common set of communication features. Coevolution may arise through the common effects of a shared environment.
For example, males in the gray tree frog species Hyla versicolor and
H. chrysoscelis both produce pulsatile calls to which gravid females are
attracted (Gerhardt 1982). Although the mean pulse rate varies between
species, it is also temperature-dependent, such that a male H. chrysoscelis
calling at 20°C could have a pulse rate similar to a male H. versicolor calling
at 15°C. In areas where the species are sympatric, this temperaturedependent property of male calls creates the potential for mating errors.
7. Neuroethology of Vocal Communication
343
Selection processes shape the acoustics of vocal communication signals.
Constraints that result from these pressures are not restricted to the signal
(i.e., input) acoustics but also the organization (i.e., state) of the representational system. In the following section, we consider a number of ways
in which the organization of the representational system is constrained by
both phylogenetic and ontogenetic processes. These constraints include
potential links between motor and sensory representations, learning, and the
relationship between species and subspecies-level recognition behaviors.
2.3.1. Motor-Sensory Linkages
2.3.1.1. Genetic Coupling and Coevolution
Signal production and perception are linked behaviorally (see Section 1;
Fitch and Hauser, Chapter 3; Ryan and Kime, Chapter 5). One possible
explanation for this parity is that the production of a class of sounds and
perception of sounds of the same class are tightly linked within each
individual. Such an arrangement could result from genetic coupling, wherein
the neural mechanisms for production and perception of a signal would
share common elements controlled by the same set of genes (Alexander
1962).Thus, modification of the genetic material would result in concomitant
changes in production and perception. Although the simplicity of this idea
is attractive, there is no guarantee that the changes will be coordinated or
that the modified element will contribute the same change, in the same direction and magnitude, for both modalities. Rather than postulate a single
genetic basis for separate production and perception systems, a more parsimonious solution is to postulate a single central pattern generator responsible for both production and perception (Bentley and Hoy 1972; Hoy et al.
1977). The predicted role of central pattern generators in perception represents an additional prediction of the genetic-coupling hypothesis.
Alternatively, the match between perception and production could result
from coevolution (von Helversen and von Helversen 1994). By this account,
the mechanisms of production and perception of communication signals are
genetically independent but evolve under reciprocal selective pressure
toward representation of a common set of communication features. Coevolution may arise through the common effects of a shared environment.
For example, males in the gray tree frog species Hyla versicolor and
H. chrysoscelis both produce pulsatile calls to which gravid females are
attracted (Gerhardt 1982). Although the mean pulse rate varies between
species, it is also temperature-dependent, such that a male H. chrysoscelis
calling at 20°C could have a pulse rate similar to a male H. versicolor calling
at 15°C. In areas where the species are sympatric, this temperaturedependent property of male calls creates the potential for mating errors.
7. Neuroethology of Vocal Communication
343