A paper appeared recently in Evolution (R.R Kerney et al., 2011 check out the link) pertaining to Dollo’s law and the re-evolution of larval characteristics in salamanders. Dollo’s law basically states that a complex phenotype once lost is unlikely to be regained. One example of a violation of this law is the development in the salamander family Plethodontidae. Salamanders either undergo metamorphosis or direct development, but the ancestral state is metamorphosis. Members of the recently derived family, Plethodontidae have for the most part direct development which is to say they pop out as mini forms of their adult counterparts. The exception to this trend is the genus Desmognathus which is nested all up in the family, but the majority of their species metamorphose. Basically you have one genus of metamorphosing species inside a massive clade with a totally different life history employing direct development. Moreover, the earliest branching lineages are direct developers. This would point to the larval characters and metamorphosis of later Desmognathus sp. as a re-evolved state.
Is this a violation of Dollo’s law?
Basically the authors examined skeletal characters from an embryo of a direct developing representative (Plethodon cinereus). Interestingly, the authors chose P. cinereus instead of comparing one of the direct developing species in Desmognathus or comparing all three.
One would expect that if these traits had re-evolved one would not see evidence of the similarity of characters in a direct developing embryo when compared to a metamorphosing specimen. Evidence was found to the contrary, and the larval characteristics were found in the developing embryo of P. cinereus. The character analysis of the hyobranchial skeleton is all very technical, but the remodeling that occurs during both embryonic development of P. cinereus is much like that of development during metamorphosis within the genus Desmognathus. The authors posit this study as “a cautionary tale” in evaluating Dollo’s law. I would agree and add this study provides evidence to suggest rethinking the way in which life-history traits are given weight in evaluating phylogeny.
Fingers-crossed for a follow-up paper that evaluates the plasticity of development and environmental pressures and interactions.
Chippindale, P.T., R.M. Bonnet, A.S. Baldwin, and J.J. Wiens. 2004. Phylogenetic evidence for a major reversal of life-history evolution in plethodontid salamanders. Evolution 58: 2809-2822.
Dollo, L., 1893. Les lois de l’evolution. Bull. Soc. Belge. Geol. Pal. Hydr. 7: 164-166.
Kerney, R.R., D.C. Blackburn, H. Muller, and J. Hanken. 2011. Do larval traits re-evolve? Evidence from the embryogenesis of a direct-developing salamander, Plethodon cinereus. Evolution 66-1: 252-262.
Titus, T., and A. Larson. 1996. Molecular phylogenetics of desmognathine salamanders (Caudata: Plethodontidae): a reevalutation of evolution in ecology, life history, and morphology. Syst. Biol. 45:451-472.