Addition of Darwin's third dimension to phyletic trees.

A three-dimensional (3D) approach for visualizing the phyletic relationship of living animals is proposed and developed as an alternative to current two-dimensional (2D) evolutionary trees. The 3D tree enhances visualization and qualitative analysis since it simultaneously provides topological (tree-structure) and spatial information (based upon genetically measured distances). However, the meaning of the third dimension, particularly its relationship to temporal processes, and further quantitative analyses emerge as open questions. Our method consists of two phases. First, a 3D representation of the genetic relationships of a related group of extant animals is produced using an optimization algorithm developed here. Second, linear connections are added to suggest a visual representation of the differing evolutionary trajectories of the organisms involved on the basis of a 2D tree algorithm. The method is applied to a set of distantly related Caenophidian snakes, and the resulting relationships are analysed. The discussions here are meant to stimulate the generation of 3D trees in the goal of complementing standard 2D views and, perhaps ultimately, improving our classification of evolutionary relationships.

Higher-level snake phylogeny inferred from mitochondrial DNA sequences of 12S rRNA and 16S rRNA genes.

Portions of two mitochondrial genes (12S and 16S ribosomal RNA) were sequenced to determine the phylogenetic relationships among the major clades of snakes. Thirty-six species, representing nearly all extant families, were examined and compared with sequences of a tuatara and three families of lizards. Snakes were found to constitute a monophyletic group (confidence probability [CP] = 96%), with the scolecophidians (blind snakes) as the most basal lineages (CP = 99%). This finding supports the hypothesis that snakes underwent a subterranean period early in their evolution. Caenophidians (advanced snakes), excluding Acrochordus, were found to be monophyletic (CP = 99%). Among the caenophidians, viperids were monophyletic (CP = 98%) and formed the sister group to the elapids plus colubrids (CP = 94%). Within the viperids, two monophyletic groups were identified: true vipers (CP = 98%) and pit vipers plus Azemiops (CP = 99%). The elapids plus Atractaspis formed a monophyletic clade (CP = 99%). Within the paraphyletic Colubridae, the largely Holarctic Colubrinae was found to be a monophyletic assemblage (CP = 98%), and the Xenodontinae was found to be polyphyletic (CP = 91%). Monophyly of the henophidians (primitive snakes) was neither supported nor rejected because of the weak resolution of relationships among those taxa, except for the clustering of Calabaria with a uropeltid, Rhinophis (CP = 94%).

Thermoregulation in a brooding female Indian python, Python molurus bivittatus.

At varying environmental temperatures, measurements of body temperatures and gas exchange of a female Indian python (Python molurus bivittatus) show that during the brooding period this animal can regulate its body temperature by physiological means analogous to those in endotherms. Ambient temperatures below 33 degrees C result in spasmodic contractions of the body musculature with a consequent increase in metabolism and body temperature.