RECONSTRUCTING ANCESTRAL REACTION NORMS - AN EXAMPLE USING THE EVOLUTION OF REPTILIAN VIVIPARITY

1. There is increasing acceptance of the ideas that tests of adaptatio nist hypotheses should consider the importance of phenotypic plasticit y for the traits involved, and explicitly incorporate the phylogeny of the organisms in question. 2. However, it is difficult to combine the se two concepts. For many cases of major Life-history shifts, transiti onal forms displaying intermediate character states no longer exist, a nd thus their reaction norms cannot be measured directly. None the les s, indirect tests may be done by using extant taxa on either side of t he relevant transition. 3. This paper provides an example of such a te st on a reproductively bimodal lizard species (Lerista bougainvillii, Gray 1839) to infer phenotypic responses to incubation temperature in the putative intermediate form between oviparity and viviparity. 4. By virtue of this tight taxonomic focus and parallel experimental manipu lations of extant taxa, predictions of alternative adaptationist hypot heses on the selective forces responsible for this evolutionary transi tion, from incubation in the nest to incubation in utero, are tested. 5. By examining the responses of offspring phenotypes to experimental manipulation of incubation conditions in the extant oviparous and vivi parous forms, it was possible to 'reconstruct' those of the now extinc t transitional form. 6. The data on phenotypically plastic responses o btained here suggest that the phylogenetic shift from oviparity to viv iparity would have induced changes in hatching times, as well as in ha tchling morphology and behaviour, in the transitional form.