In organisms that have complex life cycles, factors in the larval environment may affect both larval and adult traits. For amphibians, the postmetamorphic transition from the aquatic environment to terrestrial habitat may be a period of high juvenile mortality. We hypothesized that lipid stores at metamorphosis may affect an animal's success during this critical transition period. We examined variation in total lipid levels among years and sites in recently metamorphosed individuals of two pond-breeding salamander species, the marbled salamander (Ambystoma opacum) and the mole salamander (A. talpoideum), with limited data for one anuran species (southern leopard frog, Rana sphenocephala). Lipid levels were allometrically related to body size and ranged from 1.9 to 23.8% of body dry mass. The two salamander species differed in lipid allocation patterns, with A. opacum apportioning a higher percentage of total lipid reserves into fat bodies than A. talpoideum. Species differences in lipid allocation patterns may primarily reflect that large metamorphs will mature as one-year olds, and, regardless of species, will alter lipid compartmentalization accordingly. We used mark-recapture data obtained at drift fences encircling breeding ponds for 13 A. opacum cohorts to estimate the proportion of postmetamorphic individuals that survived to breed (age 1-4) and the mean age at first reproduction. Regression models indicated that size-corrected lipid level at metamorphosis (i.e., lipid residuals), and to a lesser extent rainfall following metamorphosis, was positively related to adult survival. Snout-vent length at metamorphosis was negatively related to age at first reproduction. We suggest that lipid stores at metamorphosis are vital to juvenile survival in the months following the transition from aquatic to terrestrial habitat, and that a trade-off shaped by postmetamorphic selection in the terrestrial habitat exists between allocation to energy stores versus structural growth in the larval environment.

Most phylogeographic studies of species from the southeastern United States have shown a simple east-west division of mtDNA variation. However, a study of the salamander Ambystoma maculatum resulted in a more complex pattern that includes a close affinity between populations from the Central Highlands of Missouri and Arkansas and the Coastal Plain separated by a genetically distinct central group of populations. We test the generality of this observation by surveying mitochondrial DNA (mtDNA) variation in the closely related species A. talpoideum. An Ambystoma-specific intergenic spacer was amplified and sequenced. The 26 resulting haplotypes varied from 380 to 800 base pairs, and alignments, including the outgroup, required 101 insertions/deletions. Sequence divergence among haplotypes ranged from 0.001 to 0.758. Population subdivision was extensive (theta = 0.64). Phylogenetic analysis of A. talpoideum mtDNA sequence reveals a close relationship between the populations from the Central Highlands and the Coastal Plain. This result is similar to that obtained for A. maculatum, although the A. talpoideum clade is not as well differentiated from its sister clades. We discuss the differences and similarities between the two Ambystoma species and previous studies and call for increased focus on multiple species with similar ecologies as a way to detect subtle biogeographic events.

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