Selective phonotaxis by males in the Majorcan midwife toad.

Males are expected to exhibit mating preferences when there is high variance in the quality of females or when males are limited to a small number of matings. In the Majorcan midwife toad, Alytes muletensis, the male performs parental care by carrying the eggs wrapped in a string around his hind legs. Both sexes possess courtship vocalizations which they use to advertise receptivity. We looked for evidence of male mating preferences in a phonotaxis arena in which males were presented with two alternative synthetic female calls. We predicted that males should prefer to mate with large females because of maternal effects on egg size, and that this preference would be manifest by selective phonotaxis toward low frequency calls. We also predicted that males should prefer high intensity calls as indicators of the energetic or motivational state of the female. Contrary to our prediction, males did not exhibit a preference for low frequency calls. The results suggest that there is stabilizing selection on call frequency and directional selection on call intensity.