We tested for predator-induced plasticity in development and growth of embryos and young tadpoles of green frogs (Rana clamitans). We expected to observe developmental plasticity in response to the leech, Macrobdella decora, because the leech represents a high, but unpredictable, risk of mortality. Embryos raised with a leech tended to delay hatching and hatched at larger size. Young tadpoles raised with a leech grew more slowly than tadpoles raised without a leech. Such changes should enhance survival of green frogs faced with the threat of leech predation.
MATERIALS AND METHODS Study species.-We collected frogs and leeches from ponds near the Queen's University Biological Station (45'34'N, 76013'W), in eastern Ontario, Canada. Green frogs breed from late May to early August in eastern Ontario. Clutches of 3500 to 4000 eggs are distributed in shallow water around the margin of permanent water bod- ies (Wright, 1914). After 3-5 days of development, embryos begin to secrete hatch enzymes and move vigorously within the egg membrane to hatch (Wright, 1914; Duellman and Trueb, 1986). Although new hatchlings are capable of swimming, they generally remain immobile.
Macrobdella decora is a large leech (up to 15 cm extended length) that is present in ponds and lakes throughout North America (Klemm, 1990). This species preys on amphibian embryos and young tadpoles and also feeds on vertebrate blood (Pennak, 1953; Howard, 1978). Frog embryos are eaten after a leech grasps the egg (or jelly surrounding the egg) with the an- terior sucker, slices through the jelly and egg membrane with its teeth, and gains access to the embryo within (GS, pers. obs.). Hatchlings are eaten whole.