Viviparity has evolved many times within squamate reptiles, mostly in cool climates, but the selective advantages of uterine retention of eggs remain obscure. Previous analyses have assumed that intrauterine incubation enhances offspring survival because of early hatching or protection of the young in utero. I suggest instead that prolonged uterine retention directly enhances hatchling viability, because eggs incubated at maternal body temperatures produce "better" hatchlings than do eggs incubated at normal nest temperatures. To test this idea, I incubated eggs of two species of montane scincid lizards from southeastern Australia (Bassiana duperreyi and Nannoscincus maccoyi) under thermal regimes designed to simulate temperatures in nests and maternal oviducts. Hatchling phenotypes were substantially affected by incubation temperatures. The variables affected by incubation at maternal versus nest thermal regimes include the hatchling's morphology (body size, relative tail length), running speed in a labo...

https://www.jstor.org/stable/info/2463002

A new hypothesis for the evolution of viviparity in reptiles

Traditional comparative studies examine evolutionary associations of traits by comparing different species, regardless of their phylogenetic relationships. A problem with such an approach is that trait values for each species are not statistically independent. This is so because species partially share evolutionary histories (Felsenstein, 1985). Another problem is that \"equilibrium\" patterns seen among extant (or tip) species may not be reflective ofpreceding evolutionary \"transformations\" (Lauder, 1981). To help circumvent these difficulties, two of us (Huey and Bennett, 1987) developed a method to analyze the correlated evolution of continuous traits within an explicitly phylogenetic context. This method was developed specifically to examine \"coadaptation\" ofphysiological and behavioral traits relating to the thermal biology ofa group ofAustralian scincid lizards. Subsequently, Martins and Garland (1991) have used computer simulation to compare the statistical properties ofthe Huey/Bennett approach, and some improvements thereof, with those of traditional non phylogenetic analyses, and of the independent contrasts method of Felsenstein (1985). In addition, new information on the relationships and divergence times of the Australian lizards in our original study has become available. We have therefore reanalyzed our data according to this new information. Most ofthe previously significant correlations between traits have been altered, with implications not only for our own study but also for the design and interpretation of comparative studies in general. Our reanalysis is timely, because interest in phylogenetically based methods for analyzing comparative data has expanded rapidly since 1987 (e.g., Felsenstein, 1988; Bell, 1989; Burt, 1989; Donoghue, 1989; Grafen, 1989; Lauder and Liem, 1989; Gittleman and Kot, 1990; Maddison, 1990, 1991; Harvey and Pagel, 1991; Lynch, 1991). Huey and Bennett (1987) examined the hypothesis that evolutionary changes in preferred body temperature (Tp ) (determined in a laboratory thermal gradient) should be positively associated (\"coadapted\") with evolutionary changes in functional thermal limits and the thermal sensitivity of sprint running speed. To index the latter, we estimated the optimal temperature for sprinting (To) (the body temperature at which animals can run fastest) for 12 species ofAustralian skinks. These values were compared to previously published determinations for lower (CTMin) and upper (CTMax) critical temperatures for the species (Bennett and JohnAlder, 1986). We applied two different analytical methods. First, following suggestions by Clutton-Brock and Harvey (1984), we tested for correlations using generic averages of traits (N = 6), because a nested ANOVA by taxonomic level indicated that 91% of the variance in T; occurred among genera. Second, to examine coadaptation in an historical framework, we developed a phylogenetic approach, overlaying the thermal data on a phylogeny of the six genera and applying a \"minimum evolution\" algorithm to estimate ancestral values at nodes. Coadaptation was again suggested by significant regressions involving inferred changes (most recent nodes to generic tips, N = 6) in To vs. T; and in CTMax vs. Tp • Because both tests indicated significant positive correlations between thermal preferences and measures of thermal sensitivity, we concluded that thermoregulatory behavior and physiology were at least partially coadapted. This conclusion appeared robust because both tests appeared conservative: although 12 species were measured, only six generic averages or inferred changes (hence 4 degrees offreedom instead of 10) were used for significance tests. However, new phylogenetic information (Baverstock and Donnellan, 1990; Greer, 1990, pers. comm.; Hutchinson et aI., 1991; S. C. Donnellan, pers. comm.) suggests that there are closer to three statistically independent taxa, not six (Fig. I). Moreover, new phylogenetic methods enable us to calculate more accurate significance tests and better estimates ofevolutionary correlations (Felsenstein, 1985, 1988; Grafen, 1989; Martins and Garland, 1991). We apply three new analytical techniques: (1) simple correlation analysis of species values, using empirical null distributions derived from computer simulation for significance testing (Martins and Garland, 1991), rather than probabilities derived from conventional tests of correlation coefficients (e.g., Zar, 1984); (2) revised minimum evolution analyses that estimate

Phylogeny and coadaptation of thermal physiology in lizards: a reanalysis.

Squamate reptiles are uniquely suited to study of evolution of reproductive mode and pattern of embryonic nutrition. Viviparous species have evolved from oviparous ancestors on numerous occasions, patterns of nutritional provision to embryos range widely from lecithotrophy, at one end of a continuum, to placentotrophy at the other, and structure and function of the maternal–embryonic relationship is highly constrained resulting in parallel evolutionary trajectories among taxa. Embryos of oviparous species primarily receive nourishment from yolk, but also mobilize a significant quantity of calcium from the eggshell. Most viviparous species also are predominantly lecithotrophic, yet all viviparous species are placentotrophic to some degree. Similarities in embryonic development and nutritional pattern between oviparous species and most viviparous species suggest that the pattern of nutrition of oviparous squamates is an exaptation for the evolution of viviparity and that placentotrophy and viviparity evolve concomitantly. The few species of squamates that rely substantially on placentotrophy have structural modifications of the interface between the embryo and mother that are interpreted as adaptations to enhance nutritional exchange. Recent studies have extended understanding of the diversity of embryonic nutrition and placental structure and have resulted in hypotheses for transitions in the evolution of placentotrophy, yet data are available for few species. Indirect tests of these hypotheses, by comparison of structural–functional relationships among clades in which viviparity has evolved, awaits further study of the reproductive biology of squamates.

Evolution of placentation among squamate reptiles: recent research and future directions.

The infrageneric phylogenetic position of the Brazilian skink Mabuya atlantica was inferred from 859 bp of the mitochondrial 16S and 12S rRNA genes. It could be shown that M. atlantica belongs to the Afro-Malagasy rather than to the South American Mabuya radiation. Mabuya atlantica probably represents an independent transmarine colonization directly from the coast of Southwest Africa, thus representing another example of the extraordinary dispersal abilities of members of this group. Moreover, the present analysis revealed that intercontinental relationships within the genus Mabuya are far more complex than previously thought. The molecular analysis suggests that Mabuya consists of several long-separated evolutionary lineages, representing distinct and well-supported monophyletic radiations. To reflect the independent origins of the South American, Asian, Afro-Malagasy and Cape Verdian groups we partition the genus Mabuya into four genera.

Phylogenetic Affinities of Mabuya atlantica Schmidt, 1945, Endemic to the Atlantic Ocean Archipelago of Fernando de Noronha (Brazil): Necessity of Partitioning the Genus Mabuya Fitzinger, 1826 (Scincidae: Lygosominae)

Molecular phylogeny of the scincid lizards of New Caledonia and adjacent areas: evidence for a single origin of the endemic skinks of Tasmantis.

The phylogenetic relationships of the Australian scincid lizards currently assigned to the genus Leiolopisma have been examined by quantitative micro-complement fixation (MC'F) comparisons of serum albumin. The results of these comparisons do not support the monophyly implicit in these species' current congeneric status, but suggest instead that the Australian species of Leiolopisma belong to several distinct phyletic lineages within the Eugongylus group. These findings are supported by several sets of non-biochemical characters, including features of scalation, osteology and karyotype. None of the Australian species shares a close relationship with the type-species of Leiolopisrna (L. telfairii), and so a new taxonomic arrangement is proposed which distributes them among the following genera: Bartleia, gen. nov. (jigurru); Bassiana, gen. nov. (duperreyi, platynotum and trilineata); Cautula, gen. nov. (zia); Niveoscincus, gen. nov. (coventryi, greeni, metallicus, microlepidotus, ocellatus, orocryptus, palfreymani and pretiosus); and Pseudemoia Fuhn, 1967 (baudini, entrecasteauxii Group 1; entrecasteauxii Group 2, rawlinsoni and spenceri). Preliminary comparisons suggest that other Leiolopisma species, from New Caledonia, Lord Howe I. and New Zealand, belong to phyletic lineages which are distinct from any of the Australian 'Leiolopisma' and from the type-species.

S Simms

Papers

Immunological Relationships and Generic Revision of the Australian Lizards Assigned to the Genus Leiolopisma (Scincidae, Lygosominae)