Blackburn, D.G. (1999a). Are viviparity and egg-guarding evolutionarily labile in squamates? Herpetologica 55: 576-573.

Abstract: Although viviparity is widely considered to evolve irreversibly from oviparity, an analysis of squamates by de Fraipont, Clobert, and Barbault in 1996 presented evidence to the contrary; it also argued that oviparous egg-guarding evolves from viviparity. The response by Shine and Lee in 1999 offers significant criticisms of this analysis and challenges its conclusions. My paper shows that the analysis by de Fraipont et al. exhibits several methodological shortcomings: use of outdated taxonomy and non-monophyletic groups, questionable codification of character states, focus on a very limited data base, analysis of taxonomic categories that are unnecessarily inclusive, and reliance on an invalid correlation between reproductive mode and body size. In comparison to the present analysis (in which 102-115 potential origins of viviparity are defined), de Fraipont et al. have focused on a small number of evolutionary transitions and have generated multiple, conflicting hypotheses about each; the result is highly inflated estimates of heterodox transformations that mainly reflect discrepant phylogenetic interpretations. I therefore support and expand upon Shine and Lee's conclusions. A reversion from viviparity to oviparity cannot be ruled out on theoretical grounds, but evidence for its occurrence among squamates thus far remains exceedingly weak.

Reprints: daniel.blackburn@mail.trincoll.edu