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A.H. Bass and C.W. Clark
Figure 2.13. Complementary explanations for existing phenotypes. Multiple explanations can be provided to account for the existence of phenotypic characters and
are best illustrated by a Venn diagram with three overlapping circles (after Bass
1998). The potential range of variation for behavioral and structural characters and
the ecological environment is represented by one of the circles. The center represents the existing phenotype, in this case low-frequency calling. Mechanistic explanations are categorized by the overlap between two circles identified here as
behavioral–structural, behavioral–ecological, and ecological–structural mechanisms.
For example, a behavioral–ecological mechanism that explains low-frequency
calling in shallow water is the influence of water depth and the substrate composition on short communication distances that guard against detection by competitors
or predators. A structural–behavioral explanation for low-frequency calling is a
rhythmically active neuromuscular system (sonic swim bladder) that generates
highly stereotyped signals. An ecological–structural explanation for low-frequency
calling is found in the direct influence of ambient water temperature on the discharge frequency of the hindbrain vocal pacemaker circuit and, in turn, an acoustic
signal’s fundamental frequency. This mechanism permits an individual to actively
vary the frequency content of its signals.
A.H. Bass and C.W. Clark
Figure 2.13. Complementary explanations for existing phenotypes. Multiple explanations can be provided to account for the existence of phenotypic characters and
are best illustrated by a Venn diagram with three overlapping circles (after Bass
1998). The potential range of variation for behavioral and structural characters and
the ecological environment is represented by one of the circles. The center represents the existing phenotype, in this case low-frequency calling. Mechanistic explanations are categorized by the overlap between two circles identified here as
behavioral–structural, behavioral–ecological, and ecological–structural mechanisms.
For example, a behavioral–ecological mechanism that explains low-frequency
calling in shallow water is the influence of water depth and the substrate composition on short communication distances that guard against detection by competitors
or predators. A structural–behavioral explanation for low-frequency calling is a
rhythmically active neuromuscular system (sonic swim bladder) that generates
highly stereotyped signals. An ecological–structural explanation for low-frequency
calling is found in the direct influence of ambient water temperature on the discharge frequency of the hindbrain vocal pacemaker circuit and, in turn, an acoustic
signal’s fundamental frequency. This mechanism permits an individual to actively
vary the frequency content of its signals.