Vocal Repertoire and Extreme Sexual Size Dimorphism in the Fijian Ground Frog Cornufer vitianus (Anura, Ceratobatrachidae)1

Abstract

The vocal repertoire of males of Cornufer vitianus from the lowland mangrove forests of Viwa Island, off the coast of Viti Levu, Fiji is described. All calls were placed into two categories: those with a high fundamental frequency, and those with a low fundamental frequency. Within each category, there is relatively high call variation. Individual males are capable of producing both the low- and high-frequency calls; some males produce predominantly the high-frequency call, others are low-frequency callers, and others alternate between the two forms. C. vitianus is among the most sexually size dimorphic amphibians known. Females were conspicuously and significantly larger than males, and we found the ratio of the mean female-to-male snout–vent lengths of 2.22. Extreme sexual size dimorphism (SSD) is a trait rare among anurans as a whole, yet is most often seen among species of the genera Cornufer and Platymantis of the western Pacific. A hypothesis is put forward relating call variability and SSD in C. vitianus.