The relative value of call embellishment in túngara frogs
- 115 Downloads
Facultative traits that have evolved under sexual selection, such as the acoustic ornaments present in the advertisement signals of male túngara frogs (Physalaemus pustulosus), offer a unique opportunity to examine selection for trait exaggeration with a focus on individual differences amongst signalers. By contrast, many studies of mate choice use experimental designs that obscure the inter-individual variation amongst signalers available for selection to act on—through the use of “typical” or average signals from the population. Here, we use dichotomous female phonotaxis choice tests to determine how the value of male call embellishment varies across 20 individual males frogs recorded from the wild—a sample which captures the acoustic diversity present in the population. We tested 20 females for each male call pair (i.e., 400 females). The results show widespread preference amongst females for ornamented calls (“whine–chucks”) over simple calls (“whines”), yet also demonstrate substantial variation in the relative benefits for individual male frogs—some males enjoy appreciable benefits by using ornaments while others (30% of males in this study) do not. We also show that the relative amplitude of the chuck to the whine correlates positively with the value of call elaborations across these 20 males. Finally, by manipulating the relative amplitude of whines and chucks using both natural and synthetic calls, we demonstrate directly that this single call parameter is key to determining the relative value of call elaborations across males.
KeywordsAdvertisement calls Individual differences Mate choice Phonotaxis Physalaemus Sexual selection
We thank X. Bernal, A. Lea, L. Ziegler, A. Dapper, and N. Lessios for assistance with data collection and the staff at the Smithsonian Tropical Research Institute for logistical support. The suggestions of two anonymous reviewers significantly improved this manuscript. Autoridad Nacional del Ambiente approved scientific permits in the Republic of Panamá. Animal use was approved by the IACUC (#06041701) at The University of Texas at Austin. This work was supported by the National Science Foundation (grant number IOB 0544096 to M. Ryan). The Homer Lindsay Bruce Endowed Fellowship supported A. Baugh.
- Andersson M (1994) Sexual selection. Princeton University Press, PrincetonGoogle Scholar
- Dale J (2006) Intraspecific variation in coloration. In: Hill GE, McGraw KJ (eds) Bird coloration: volume 2, function and evolution. Harvard University Press, Cambridge, pp 36–86Google Scholar
- Darwin C (1871) The descent of man, and selection in relation to sex. Murray, LondonGoogle Scholar
- Espmark Y (1995) Individual and local variations in the song of the snow bunting Plectrophenax nivalis on Spitzbergen. Bioacoustics 6:117–134Google Scholar
- Gerhardt HC, Schwartz JJ (2001) Auditory tuning and frequency preferences in anurans. In: Ryan MJ (ed) Anuran communication. Smithsonian, Washington, D.C., pp 73–85Google Scholar
- Rand AS, Ryan MJ, Wilczynski W (1992) Signal redundancy and receiver permissiveness in acoustic mate recognition by the túngara frog, Physalaemus pustulosus. Am Zool 32:15–17Google Scholar
- Ryan MJ (1985) The túngara frog: a study in sexual selection and communication. University of Chicago Press, ChicagoGoogle Scholar
- Ryan MJ, Rand AS (2001) Feature weighting in signal recognition and discrimination by túngara frogs. In: Ryan MJ (ed) Anuran communication. Smithsonian Institution, Washington, D.C., pp 86–101Google Scholar