Female preference in complex acoustical environments in the midwife toads Alytes obstetricans and Alytes cisternasii

Gravid females of Alytes obstetricans and Alytes cisternasii were tested with synthetic calls in seven-speaker playback tests. A first, "mean-centered" test presented calls with frequencies representing an array of different calls spanning over the range of the population (+/-2.25 SD). In this test, Females of both species approached a synthetic call that was lower than the average call frequency of the male population although the difference was significant only for A. obstetricans. The regression between female weight and size and preferred frequency was not significant in either species. These results confirm the reported trends of females preferring lower frequency calls (corresponding to larger males) based on two-speaker playback tests for A. obstetricans. For A. cisternasii, the lack of significance of the seven-speaker test suggests that the preference trend previously found in two-speaker tests may be obscured in more complex acoustical environments. A second "supernormal stimulus" test presented females with calls ranging from the lowest frequency values of the male population (-2.25 SD) and lower, up to -6.75 SD beyond the range. In both species females preferentially approached calls higher than the mean frequency of the stimulus presented. This result suggests that in both cases selection for low frequencies is not open ended, and that the preferred Frequency is within the range of the male population.