Water balance of terrestrial anuran (Eleutherodactylus Coqui) eggs: importance of parental care

Abstract

The terrestrial eggs of the coqui of Puerto Rico are brooded almost continuously by the male parent from the time of oviposition until the fully metamorphosed hatchlings emerge from the eggs 15-20 d later. The gelatinous layer surrounding each egg offers no resistance to the exchange of water by the egg, and rates of exchange are determined by microclimatic conditions, structural characteristics of the nest, and the behavior of the male frog . During development in natural nests, the eggs experience a three- to fourfold increase in mass. Laboratory experiments coupled with field observations indicate that this increase is the result of the transfer of liquid water from the incubating male to his eggs. The transfer is driven by a difference in water potential between the eggs and the body fluids of the male frog that is nearly constant throughout incubation, despite an increase in egg mass. Eggs must take up water during incubation. Eggs that do not experience an increase in mass during development either die or produce small hatchlings. A water uptake that doubles the initial mass of the egg is necessary to produce a full-size hatchling with normal tissue water content.