Early limb patterning in the direct-developing salamander Plethodon cinereus revealed by sox9 and col2a1.

Direct-developing amphibians form limbs during early embryonic stages, as opposed to the later, often postembryonic limb formation of metamorphosing species. Limb patterning is dramatically altered in direct-developing frogs, but little attention has been given to direct-developing salamanders. We use expression patterns of two genes, sox9 and col2a1, to assess skeletal patterning during embryonic limb development in the direct-developing salamander Plethodon cinereus.

Cartilage on the move: cartilage lineage tracing during tadpole metamorphosis.

The reorganization of cranial cartilages during tadpole metamorphosis is a set of complex processes. The fates of larval cartilage-forming cells (chondrocytes) and sources of adult chondrocytes are largely unknown. Individual larval cranial cartilages may either degenerate or remodel, while many adult cartilages appear to form de novo during metamorphosis.

Do larval traits re-evolve? Evidence from the embryogenesis of a direct-developing salamander, Plethodon cinereus.

Recent molecular phylogenies suggest the surprising reacquisition of posthatching metamorphosis within an otherwise direct-developing clade of lungless salamanders (family Plethodontidae). Metamorphosis was long regarded as plesiomorphic for plethodontids, yet the genus Desmognathus, which primarily includes metamorphosing species, is now nested within a much larger clade of direct-developing species. The extent to which the putative reacquisition of metamorphosis in Desmognathus represents a true evolutionary reversal is contingent upon the extent to which both larva-specific features and metamorphosis were actually lost during the evolution of direct development.