LERISTA BOUGAINVILLII, A CASE-STUDY FOR THE EVOLUTION OF VIVIPARITY IN REPTILES

Many factors, both environmental and biotic, have been suggested to fa cilitate or hinder the evolution of viviparity (live-bearing) in repti les. Viviparity has evolved recently within the Australian scincid liz ard Lerista bougainvillii and the species includes oviparous, viviparo us, and reproductively intermediate (with prolonged egg retention) pop ulations; thus, it offers an exceptional opportunity to evaluate the v alidity of these hypotheses. We carried out such tests by (i) comparin g environmental conditions over the geographic ranges occupied by ovip arous, viviparous, and intermediate populations (to identify possible selective forces for the evolution of viviparity), and (ii) comparing morphological, reproductive and ecological traits of L. bougainvillii with those of other sympatric scincid species (to identify traits that may have predisposed this taxon to the evolution of viviparity). The areas occupied by viviparous L. bougainvillii are significantly colder than those occupied by both their intermediate and oviparous conspeci fics, in accord with the ''cold-climate'' hypothesis for reptilian viv iparity. Rainfall is similar over the ranges of the three forms. Clima tic unpredictability (as assessed by the magnitude of year-to-year the rmal variation) is lower for viviparous animals, in contradiction to p ublished speculations. Comparison with 31 sympatric scincid species sh owed that L. bougainvillii Is not atypical for most of the traits we m easured (e.g., body size, clutch size, thermal preferenda and toleranc es). However, oviparous L. bougainvillii do display several traits tha t have been suggested to facilitate the evolution of viviparity. For e xample, pregnancy does not reduce locomotor ability of females; the li zards are semi-fossorial; even the oviparous females produce only a si ngle clutch of eggs per year; and they ovulate relatively late in summ er, so that the time available for incubation is limited.