Experimental studies of complex life cycles in plethodontid salamanders are reviewed and evaluated in the context of seven theoretical life-history models that focus on amphibians having biphasic life cycles. Such life cycles are found in the single species of the subfamily Hemidactylinae and in some members of the subfamily Spelerpinae and genus Desmognathus. In general, data on plethodontids provide only limited support for the predictions of the models. Given that the models have been formulated mainly for pond-breeding amphibians, several investigators have suggested that ancestral adaptation to streams in biphasic plethodontids have prescribed different evolutionary trajectories in the metamorphic response of these salamanders, in comparison with pond-breeding frogs and salamanders.
Larval and metamorphic characters tabulated for biphasic plethodontids show that there is considerable inter- and intraspecific variation in larval periods and sizes at metamorphosis. In all lineages, in most species, metamorphosis is concentrated in the late spring and summer. However, spelerpines and desmognathans differ markedly in the phenology of oviposition-nesting. Among spelerpine species, oviposition may occur in any season, whereas in desmognathans oviposition is usually restricted to late spring and summer. This represents another instance of life-history symmetry in desmognathans, and may reflect an effect of genetic and developmental constraints in this lineage.