MOLECULAR PHYLOGENETICS OF SEXUAL AND PARTHENOGENETIC TIMEMA WALKING-STICKS

We inferred a phylogeny for the walking-stick genus Timema (Insecta: P hasmatoptera) using mitochondrial DNA sequence, and we used the phylog eny to infer temporal patterns of speciation and the evolutionary hist ory of parthenogenesis. Maximum parsimony, neighbour-joining and maxim um-likelihood analyses of 660 base pairs (bp) of cytochrome oxidase I (COT) yielded phylogenies that were well resolved and topologically id entical or very similar. Application of an insect molecular clock for COI suggests that the genus originated in southern California, norther n Mexico or Arizona about 20 million years ago and underwent a burst o f speciation 1.5-3 million years ago during the uplifts of the Sierra Nevada, Coast, and Transverse Ranges. The phylogeny indicates that the three parthenogenetic lineages of Timema have arisen independently an d are each closely related to morphologically indistinguishable or sim ilar sexual species. Each of the three lineages exhibits an allopatric or parapatric, and more northerly, distribution with regard to their closest sexual relative. COI divergence levels between each of the thr ee parthenogens and their closest sexual relative suggest ancient orig ins of parthenogenesis, 1.5-3 million years ago, that may coincide wit h the extensive glaciation that formed the North American ice sheets.