“temperature cricket” is so called because of the reliability of its pulse rate
in predicting ambient temperature (Ewing 1989). How do receivers respond
to such scaling effects in signals?
In anurans, the tuning of one or both of the two peripheral end organs
that are sensitive to airborne sound tends to match the dominant spectral
characteristics of the long-distance advertisement call (Fuzessery 1988;
Zakon and Wilczynski 1988). The amphibian papilla (AP) tends to be most
sensitive at threshold to frequencies below about 1,200 Hz, whereas the
basilar papilla (BP) is most sensitive to frequencies above 1,200 Hz.
Depending on the spectral distribution of call energy, either or both end
organs will exhibit a match between the frequencies to which they are most
sensitive and the spectral concentrations of call energy.
The AP and BP differ in a number of ways. The AP is thought to accommodate a traveling wave and has an array of hair cells that are tonotopically organized. The BP, on the other hand, has most of its hair cells tuned
to similar frequencies, and the overall frequency sensitivity of the BP might
result from its resonating properties, which will be influenced by size
(Keddy-Hector et al. 1992; Wilczynski et al. 1992).
Cricket frogs, Acris crepitans, produce long-distance calls with most of the
energy above 3,000 Hz. It seems clear that the BP rather than the AP is critical in the initial processing of the call. Calls exhibit a large amount of variation in dominant frequency across the geographical range of the species,
but the auditory system tends to be tuned to frequencies characteristic of
(Capranica et al. 1973; Ryan and Wilczynski 1988) or slightly lower than
(Ryan et al. 1992) the local population. The geographic covariation of call
frequency and auditory tuning might result from pleiotropic effects of
changes in body size—both factors are negatively correlated with body size
(Nevo and Capranica 1985; Ryan and Wilczynski 1991; Keddy-Hector et al.
1992;Wilczynski et al. 1992). It is assumed that the effect on tuning is derived
from the effect of size on the resonating properties of the BP (Fig. 5.5).
These results are consistent with patterns of frequency preference for call
dominant frequency (Ryan and Wilczynski 1988; Ryan et al. 1992).
There are some cautions necessary, however. These scaling effects vary
among populations (Keddy-Hector et al. 1992; Wilczynski et al. 1992), the
relationships are not always very tight, and the preferences for call frequency appear to be statistically weak (although they could still generate
strong biases in male mating success in the field). Nevertheless, dual scaling
of signal and receiver to body-size variation does offer the potential for
maintaining the functional integration of signal and receiver when size
diverges among species or populations, and this will be true whether or not
size has a significant heritable component.
A more short-term scaling problem involves temperature effects on
signal characteristics. In most insects and frogs, temporal features of the
call, such as pulse repetition rate, are drastically affected by temperature
variation (Zweifel 1968; Gerhardt 1978; Bauer and Helverson 1987; Ewing
1989; Wagner 1989). In general, call rates increase with temperature. Tem248
M.J. Ryan and N.M. Kime
in predicting ambient temperature (Ewing 1989). How do receivers respond
to such scaling effects in signals?
In anurans, the tuning of one or both of the two peripheral end organs
that are sensitive to airborne sound tends to match the dominant spectral
characteristics of the long-distance advertisement call (Fuzessery 1988;
Zakon and Wilczynski 1988). The amphibian papilla (AP) tends to be most
sensitive at threshold to frequencies below about 1,200 Hz, whereas the
basilar papilla (BP) is most sensitive to frequencies above 1,200 Hz.
Depending on the spectral distribution of call energy, either or both end
organs will exhibit a match between the frequencies to which they are most
sensitive and the spectral concentrations of call energy.
The AP and BP differ in a number of ways. The AP is thought to accommodate a traveling wave and has an array of hair cells that are tonotopically organized. The BP, on the other hand, has most of its hair cells tuned
to similar frequencies, and the overall frequency sensitivity of the BP might
result from its resonating properties, which will be influenced by size
(Keddy-Hector et al. 1992; Wilczynski et al. 1992).
Cricket frogs, Acris crepitans, produce long-distance calls with most of the
energy above 3,000 Hz. It seems clear that the BP rather than the AP is critical in the initial processing of the call. Calls exhibit a large amount of variation in dominant frequency across the geographical range of the species,
but the auditory system tends to be tuned to frequencies characteristic of
(Capranica et al. 1973; Ryan and Wilczynski 1988) or slightly lower than
(Ryan et al. 1992) the local population. The geographic covariation of call
frequency and auditory tuning might result from pleiotropic effects of
changes in body size—both factors are negatively correlated with body size
(Nevo and Capranica 1985; Ryan and Wilczynski 1991; Keddy-Hector et al.
1992;Wilczynski et al. 1992). It is assumed that the effect on tuning is derived
from the effect of size on the resonating properties of the BP (Fig. 5.5).
These results are consistent with patterns of frequency preference for call
dominant frequency (Ryan and Wilczynski 1988; Ryan et al. 1992).
There are some cautions necessary, however. These scaling effects vary
among populations (Keddy-Hector et al. 1992; Wilczynski et al. 1992), the
relationships are not always very tight, and the preferences for call frequency appear to be statistically weak (although they could still generate
strong biases in male mating success in the field). Nevertheless, dual scaling
of signal and receiver to body-size variation does offer the potential for
maintaining the functional integration of signal and receiver when size
diverges among species or populations, and this will be true whether or not
size has a significant heritable component.
A more short-term scaling problem involves temperature effects on
signal characteristics. In most insects and frogs, temporal features of the
call, such as pulse repetition rate, are drastically affected by temperature
variation (Zweifel 1968; Gerhardt 1978; Bauer and Helverson 1987; Ewing
1989; Wagner 1989). In general, call rates increase with temperature. Tem248
M.J. Ryan and N.M. Kime