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ABSTRACT.-Male giant bullfrogs Pyxicephalus adspersus exhibit paternal care through construction of channels that guide tadpoles to larger bodies of water. We found the following. These channels (which may exceed 15 m in length) make available cooler water to broods in the rapidly drying breeding puddles that frequently reach critically high temperatures. Eggs of P adspersus exposed to temperatures above 38*C died, a temperature reached in a third of the puddles measured. In contrast, tadpoles readily survived temperatures above 38 deg C, and experiments showed that tadpoles can survive the highest temperatures recorded at the puddles. Males actively defended their offspring against predators and were sometimes killed while performing this behavior. Survival of eggs and larvae in territorial broods was roughly twice that of broods in nonterritorial breeding arenas. The large cost of paternal care in the giant bullfrog is therefore offset by strong fitness gains. We suggest that channel construction and predator defence, crucial for tadpole survival, can be performed most efficiently by large-bodied parents, explaining why males (not the smaller females) perform parental care.
Parental care has been reported in a number of frogs (Townsend, 1986; Summers, 1989; Kok et al., 1989), most of these from terrestrial breeders in the tropics (Wells, 1981). Either males or females can perform parental care. Paternal care is more likely in frogs than in other vertebrates because the cost of paternal care is usually low (Wells, 1981). This is exemplified in territorial species where eggs or tadpoles are deposited...