Call Rate Variability and Female Choice in the African Frog, Hyperolius Marmoratus

Abstract

1. Two-choice phonotaxis experiments were used to investigate female responses to short-term variation in call timing in the African painted reed frog, Hyperolius marmoratus. The number of calls produced per stimulus in each choice test were equalised over either 10 or 20 seconds. 2. All alternative stimuli were tested against a regular stimulus with an invariant inter-call interval (ICI = duration between the onset of successive calls). There were three categories of alternative call timing; bouts of rapid calling (short ICI) where the period of silence between bouts was shorter than the bouts of calling; bouts of rapid calling where the period of silence between bouts was longer than the bout of calling; and irregular calling (variable ICI) without prolonged periods of silence. 3. The only stimuli females discriminated against were rapid bouts of calling with prolonged periods of silence. Females showed significant differences in the number of responses when presented with two stimuli that differed in call timing over as short a period as 10 seconds. 4. We also calculated variability in the ICI of 25 males in the field. There was a significant negative relationship between mean call rate (calls/min) and variability in the ICI. Faster callers showed lower variability in ICI. 5. The phonotaxis experiments did not show a female preference for regular versus irregular call timing. So female mate choice of males with higher call rates in the field is not due to a preferencc for males with less variability in ICI.