The Herpetological Journal

pp.35-42

Authors: J. R. Downie

Abstract: At 28°C, isolated Physalaemus pusrulosus eggs hatch after approximately 40 hours incubation. However. few tadpoles emerge from foam nests at this time. From nests incubated so that the foam remains moist. emergence occurs progressively over the next day. If the foam is allowed to dry on top, complete emergence takes even longer. Manipulation of the incubation environment shows that emergence is not stimulated by dark or light, nor does it occur at a particular time of day. Since hatching occurs at Gosner stage 21 and the last tadpoles to emerge from foam have reached Gosner stage 23-24, it is suggested that late emergence allows hatchlings to continue development to a more advanced stage in a protected environment: the foam acts as a post-hatching refuge. However, it is also shown that tadpoles emerging early are able to grow to Gosner stage 25 by the time the last tadpoles leave the nest: remaining in the nest therefore bears a cost. In addition. part of the delay in emergence may simply result from the time small tadpoles take to wriggle free from a large mass of cohesive foam.