in the amount of time males spend calling. In many species, there are often
alternative mating strategies in which one type of male signals for mates
while the other does not and instead attempts to sneak copulations with
females (Cade 1981). In crickets, these differences among males are attributable to genetic differences. Cade’s studies of crickets are an illustration
of how the costs of acoustic signaling can result in the evolution of genetically influenced variation in male mating behavior.
Risk of parasitism and predation does not only vary with the amount of
signaling but with other environmental variables as well, and these are
taken into account by female crickets when responding to calls. Hedrick
and Dill (1993) showed that female response to attractive versus unattractive calls is influenced by the amount of cover in the environment. In situations that afford cover from parasites and predators, female crickets are
more likely to respond to attractive calls perceived to be farther away.When
the females are more exposed, they choose the closer, although what in
other circumstances would be less attractive, call.
There are also adaptations on the side of the eavesdropper in this system.
Robert et al. (1992) show that the tuning characteristics of the fly’s hearing
match the spectral energy of the cricket’s call. Thus, there has been an evolutionary convergence between the fly’s hearing and the cricket’s call. The
hearing sensitivity of the parasitoid fly appears to be an evolutionarily
derived character that evolved because of the benefits derived by female
flies in locating a host for their larvae.
4.1.2. The Frog-Eating Bat and Calling Frogs
A vertebrate analog to the fly–cricket system is that of the frog-eating bat
and calling frogs. Trachops cirrhosus is a neotropical bat that feeds on a
variety of frogs and uses the frog’s advertisement call as a localization cue
(Fig. 5.4; Tuttle and Ryan 1981). As with the fly–cricket system, Trachops
has a number of effects on the communication system of frogs. Male túngara
frogs (Physalaemus pustulosus) produce a whine-like advertisement call
that is both necessary and sufficient to attract females. Males can add up to
six chucks to the call; chucks are short duration (35 msec), harmonically
rich (fundamental frequency of about 250 Hz, with up to 15 harmonics)
sounds. The addition of chucks increases the call’s attractiveness. Although
Trachops are attracted to and able to localize calls without chucks, when
given a choice they prefer calls with chucks. Thus, the interaction of sexual
selection for calls with more chucks and natural selection for calls with
fewer chucks seems to have resulted in the evolution of the túngara frog’s
advertisement call of facultatively varying complexity (Ryan et al. 1982).
Bat predation also influences how and when males call. Male túngara
frogs exhibit more evasive behavior, such as submerging under the water,
and are less likely to resume calling after the close approach of a bat (Tuttle
et al. 1982). Smilisca sila males produce calls that overlap in time with one
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M.J. Ryan and N.M. Kime
alternative mating strategies in which one type of male signals for mates
while the other does not and instead attempts to sneak copulations with
females (Cade 1981). In crickets, these differences among males are attributable to genetic differences. Cade’s studies of crickets are an illustration
of how the costs of acoustic signaling can result in the evolution of genetically influenced variation in male mating behavior.
Risk of parasitism and predation does not only vary with the amount of
signaling but with other environmental variables as well, and these are
taken into account by female crickets when responding to calls. Hedrick
and Dill (1993) showed that female response to attractive versus unattractive calls is influenced by the amount of cover in the environment. In situations that afford cover from parasites and predators, female crickets are
more likely to respond to attractive calls perceived to be farther away.When
the females are more exposed, they choose the closer, although what in
other circumstances would be less attractive, call.
There are also adaptations on the side of the eavesdropper in this system.
Robert et al. (1992) show that the tuning characteristics of the fly’s hearing
match the spectral energy of the cricket’s call. Thus, there has been an evolutionary convergence between the fly’s hearing and the cricket’s call. The
hearing sensitivity of the parasitoid fly appears to be an evolutionarily
derived character that evolved because of the benefits derived by female
flies in locating a host for their larvae.
4.1.2. The Frog-Eating Bat and Calling Frogs
A vertebrate analog to the fly–cricket system is that of the frog-eating bat
and calling frogs. Trachops cirrhosus is a neotropical bat that feeds on a
variety of frogs and uses the frog’s advertisement call as a localization cue
(Fig. 5.4; Tuttle and Ryan 1981). As with the fly–cricket system, Trachops
has a number of effects on the communication system of frogs. Male túngara
frogs (Physalaemus pustulosus) produce a whine-like advertisement call
that is both necessary and sufficient to attract females. Males can add up to
six chucks to the call; chucks are short duration (35 msec), harmonically
rich (fundamental frequency of about 250 Hz, with up to 15 harmonics)
sounds. The addition of chucks increases the call’s attractiveness. Although
Trachops are attracted to and able to localize calls without chucks, when
given a choice they prefer calls with chucks. Thus, the interaction of sexual
selection for calls with more chucks and natural selection for calls with
fewer chucks seems to have resulted in the evolution of the túngara frog’s
advertisement call of facultatively varying complexity (Ryan et al. 1982).
Bat predation also influences how and when males call. Male túngara
frogs exhibit more evasive behavior, such as submerging under the water,
and are less likely to resume calling after the close approach of a bat (Tuttle
et al. 1982). Smilisca sila males produce calls that overlap in time with one
240
M.J. Ryan and N.M. Kime