Download Physalaemus pustulosus

Physalaemus pustulosus –
The Tungara Frog
• Ranges from tropical Mexico to northern South America
• Averages about 35 mm in snout-vent length
• Breeds in temporary bodies of water – even hoof prints
Males produce an advertisement call to which females
respond. The call consists of two components. One is a
frequency-modulated downward sweep (the “whine”
component).
Whine
When several males are calling simultaneously, they
may increase the complexity of their call by adding
one or more “chuck” components.
Chuck
Playback experiments
have shown that females
respond preferentially to
the calls that have the
most chuck components,
that is, to the most
complex calls.
Why then don’t all males always produce the most
complex calls possible, if females “prefer” the more
complex calls?
The Tungara Frog, among
others, is preyed upon by a
species of bat, Trachops
cirrhosus. In near total
darkness, the bat locates the
frog on the basis of the frog’s
advertisement call. The whine
component is difficult to
localize, but the source of the
chuck component is much
more easily located.
The complexity of male
advertisement calls is therefore a
compromise between sexual
selection, operating as female
choice to favor more complex
calls, and natural selection in the
form of predation by the bat,
favoring simple calls that are
difficult for predators to locate.
Thus, when few males are calling
and there is little competition for
females, frogs emit relatively
simple calls. Only when malemale competition is intense does
it “pay” males to emit the risky
complex calls that females favor.