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Preferences for Call Spectral Properties in Hyla intermedia


Sergio Castellano, Dipartimento di Biologia Animale e dell'Uomo, Via Accademia Albertina, 13, 10123 Torino, Italy. E-mail:


We studied the pattern of variation in the spectral properties of male advertisement calls and female preference functions for these same properties in the Italian treefrog (Hyla intermedia). The call spectral properties (fundamental and dominant frequencies) were highly negatively correlated with body size, they showed low within-individual variation, and, at the population level, they were found to be under weak stabilizing selection. In two-choice discrimination tests, females did not show preferences between calls with fundamental and dominant frequencies within two standard deviations from the population mean, whereas females significantly discriminated against calls when their frequencies were three (or more) standard deviations above or below the population mean. Consistent with the observed permissiveness in female preference over the call spectral structure, in the natural population, we found no evidence either of directional selection on male body size or of a size-assortative mating pattern. The pattern of preferences observed at the population level did not mirror the preferences of individual females. In fact, in a multi-trial discrimination experiment, females showed significant differences in their choice between the average frequency call and a two standard deviation lower than average frequency alternative, for which no significant preferences were observed at the population level. Variations in preference were not found to correlate with female body size.