Aspects of the ecology and breeding biology of the African bullfrog, pyxicephalus adspersus

Abstract

The African Bullfrog, Pyxicephalus adspersus, is highly sexually dimorphic with adult males exceeding 1 kg in body mass and females rarely exceeding 200g. Bullfrogs are extreme explosive breeders completing mate acquisition, amplexus, and oviposition within 48 hours. Territorial males then remain with their tadpoles until metamorphosis 32-37 days later. I observed mating behaviour and parental care in two marked populations of bullfrogs over three breeding events during the 1992-93 and 1993-94 wet seasons (October-January). Adult males exhibit three distinct size-related mating tactics namely territorial, non-territorial and satellite behaviour. Here I consider variation in mating success between these three categories of males. Territorial frogs were the largest, most aggressive males and showed intolerance to any intruding conspecific males. Non-territorial frogs gathered in large groups in certain areas of the pan and compete to mate with females that did not mate with territorial males. Competitive interactions between these males were characterised by numerous attempts at amplexus displacement. Satellite frogs were the smallest adult males who adopted concealed non-calling, non-aggressive positions close to territorial males. Satellites attempted to intercept females attracted to territory residents. Only territorial males remain behind and defend their tadpoles against predators. The presence of territorial males has a positive effect on tadpole survival. Territorial males also construct channels between their tadpole 'nurseries' and the main body of water. These channels function as a means of tadpole movement and also a mechanism whereby males regulate water depth in the nursery to provide optimal conditions for larval development. Bullfrog offspring are adapted for survival in their unpredictable ephemeral breeding habitats by having two different tadpole morphs. A large, rapidly developing carnivorous tadpole which completes its larval development in 19-21 days and a normal developing, omnivorous tadpole which complete metamorphosis after 31-3 5 days. Tadpoles are also able to survive extreme temperatures of up to 3 9°C in their shallow temporary ponds.