Why is double clutching rare in the Majorcan midwife toad?

Abstract

In species with male parental care, multiple clutching is the provisioning of care to the eggs or offspring of two or more females simultaneously. Multiple clutching represents a strategy by which males reduce the reproductive costs associated with male parental care relative to the reproductive gains. Although multiple clutching is common in two species of midwife toads ( Alytes obstetricansand A. cisternasii), double clutching in the Majorcan midwife toad, A. muletensis, is rare and triple clutching has never been observed. In this paper, the reasons for the low frequency of double clutching in A. muletensisrelative to the other species are examined. Two hypotheses were experimentally disproved: double clutching is not limited to particularly large males, and females do not prefer to mate with non-brooding than brooding males. The low incidence of double clutching in A. muletensisappears to result from a time constraint on males. Males only advertise for second clutches within 3 days of the first. This time limit may have evolved as a result of energetic constraints on either the duration of the brooding period of males, or the developmental plasticity of larvae. A model was constructed which illustrates that if females mate randomly with respect to the brooding status of males, the time limit for obtaining a second clutch partially explains the differences in frequencies of double clutching observed between A. muletensisand the other species of midwife toads. The female inter-clutch interval and the male brooding period are also likely to contribute significantly to the rate of double clutching in a population.