A Comparison of the Life Histories of Coastal and Montane Populations of Ambystoma macrodactylum in California

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Abstract
The disjunct, coastal endemic Ambystoma macrodactylum croceum was compared with 2 populations of A. m. sigillatum (1980 and 2450 m) from the Sierra Nevada of California. A. m. croceum and A. m. sigillatum 1980 in breed in temporary ponds, but A. m. sigillatum at 2450 m requires permanent ponds. The last has a 14-month larval period with a 2-3 month overlap of larval age classes, whereas the others have a short (3-4 months) larval period. A. m. croceum breeds in January and February, A. m. sigillatum from late May (1980 m) through June (2450 m). In all areas climatic conditions control the primary activities. Rainfall is the only important governing factor for A. m. croceum. It controls the breeding migration, dispersal of juveniles, time of breeding, and (because it determines the length of time the ponds persist) determines size attained at metamorphosis. For A. m. sigillatum the most important factor is temperature, determining the time of breeding (thaw) and the larval and adult growth rates. A. m. croceum deposits eggs singly on vegetation near the surface in shallow water. In A. m. sigillatum eggs are clustered under logs and bark near the bottom in the deeper portions of the ponds. Size at metamorphosis is approximately the same in A. m. croceum (37.5 mm S-V) and A. M. sigillatum from 2450 m (37.8) but the former attains this size in 90-140 days whereas the latter requires 14 months. The A. m. sigillatum from 1980 m metamorphose after 80-90 days, at 25.0 mm S-V, approximately the size reached by the 2450 m population after the first growing season. Metamorphosis seems to be triggered by intrinsic factors in A. m. sigillatum at 2450 m but by extrinsic factors (drying of the ponds) in the others. The larvae of A. m. croceum are secretive at all stages but their behavior varies and has been generally correlated with stage of development. Larval A. m. sigillatum (2450 m) are secretive in hatchling and metamorphic stages but active in open, illuminated portions of the ponds otherwise. The breeding migration of A. m. croceum is stimulated by heavy rainfall and takes place only on rainy nights. The migration of A. m. sigillatum was not observed but occurs while snow and some ice are present. Sexual maturity is reached during the second year of life in A. m. croceum, during the third year in A. m. sigillatum from 2450 m. Both A. m. croceum and the Sierran A. m. sigillatum are derived from ancestral populations to the north. The isolated A. m. croceum shows the greatest divergence in life history compared to present-day northern populations.