LIFE-HISTORY VARIATION ACROSS A HYBRID ZONE IN GEOCRINIA EMBRYONIC-DEVELOPMENT AND LARVAL GROWTH (AMPHIBIA, ANURA, MYOBATRACHINAE)

Egg masses were collected at eleven sites across a hybrid zone between the Australian frog species Geocrinia laevis and Geocrinia victoriana . Spawning occurred over a period of several weeks in both species and in hybrid populations. Embryonic development was faster in G. victori ana, the species with the larger eggs, than in G. laevis. Embryonic mo rtality showed considerable variation, but was not elevated in the cen tre of the hybrid zone. Twenty tadpoles of each sibship were raised un der standardized conditions, to compare patterns of growth and develop ment. Larval survival was generally high. Growth rates, estimated from length increment during the first three weeks, were negatively correl ated with time of embryonic development (from stage 17 to 26), but sho wed no significant correlations with size at hatching, differentiation rate and time to metamorphosis. Growth rates were highest in genetica lly intermediate hybrids. Time to metamorphosis was negatively related to size at hatching, but positively correlated with body length and w ith an index of relative differentiation (SOKOL, 1984) at metamorphosi s. Geocrinia victoriana transformed earlier and at smaller sizes than G. laevis and hybrids genetically closer to the latter species.