The 'multitasking hypothesis' for complex signal function predicts performance trade-offs between signal components that negatively covary (e.g. due to energetic or mechanical constraints) and receiver preferences for more extreme values of the negatively covarying components that are difficult to produce simultaneously. We tested these two predictions in Cope's grey treefrogs, Hyla chrysoscelis. In a field study, we recorded and analysed 1000 advertisement calls from males calling in breeding choruses to test the prediction that two signal components important in female mating decisions (call rate and call duration) negatively covary under natural conditions. In a laboratory study, we conducted phonotaxis tests with female subjects to test the prediction that females prefer calls with higher overall 'call efforts' (the product of call rate. × call duration). Consistent with predictions of the multitasking hypothesis, call rate and call duration were significantly negatively related and females preferred calls produced with higher call efforts, manifested through preferences for greater values of both call rate and call duration. We conducted an additional playback experiment to test the hypothesis that males increase their call effort in competitive situations to maximize their attractiveness to females. Compared to quiet conditions, male subjects increased their call duration and decreased their call rate, but did not alter call effort, in response to a simulated calling neighbour or broadcasts of chorus noise. Together our data have implications for understanding the function of multicomponent signals when signallers must balance performance trade-offs in mate attraction with dynamic signal modifications in other social contexts.
Bibliographical noteFunding Information:
We are grateful to all members of the lab, especially Sandra Tekmen, for their assistance with collecting frogs and running trials. We are also grateful to Josh Schwartz for comments on an earlier version of the manuscript. This research was supported by a National Science Foundation (NSF) grant ( IOS 0842759 ) to M.A.B. and an NSF Graduate Research Fellowship to E.K.L. All experimental procedures were approved by the University of Minnesota Institutional Animal Care and Use Committee (number 0809A46721, number 1202A10178).
Copyright 2013 Elsevier B.V., All rights reserved.
- Condition dependent
- Female preference
- Gray treefrog
- Hyla versicolor
- Multicomponent signal
- Performance trade-off