1. There is increasing acceptance of the ideas that tests of adaptationist hypotheses should consider the importance of phenotypic plasticity for the traits involved, and explicitly incorporate the phylogeny of the organisms in question.
2. However, it is difficult to combine these two concepts. For many cases of major life-history shifts, transitional forms displaying intermediate character states no longer exist, and thus their reaction norms cannot be measured directly. None the less, indirect tests may be done by using extant taxa on either side of the relevant transition.
3. This paper provides an example of such a test 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 manipulations of extant taxa, predictions of alternative adaptationist hypotheses on the selective forces responsible for this evolutionary transition, 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 viviparous forms, it was possible to 'reconstruct' those of the now extinct transitional form.
6. The data on phenotypically plastic responses obtained here suggest that the phylogenetic shift from oviparity to viviparity would have induced changes in hatching times, as well as in hatchling morphology and behaviour, in the transitional form.
- evolution of viviparity
- Lerista bougainvillii