BRANCHIOPOD PHYLOGENETIC RECONSTRUCTION FROM 12S RDNA SEQUENCE DATA

Nucleotide sequences from mitochondrial 12S ribosomal DNA are determin ed for 7 species of branchiopod crustaceans: 2 from the order Anostrac a (Streptocephalus texanus and Linderiella santarosae), 2 from the ord er Conchostraca (Cyzicus mexicanus and Eulimnadia texana), 2 from the order Notostraca (Triops longicaudatus and Lepidurus bilobatus), and o ne from the order Cladocera (Moina brachycephala). They are compared t o other branchiopod (Anostraca: Artemia franciscana, Cladocera: Daphni a pulex), and maxillopod (Branchiura: Savignium crenatum) sequences fr om the literature. The total set of nucleotides analyzed consists of s equences ranging in length from 250-267 bases. Multiple sequence align ments are generated and compared to assess the effects of alignment am biguity on phylogenetic inference. Comparison of sequences among taxa revealed that (1) there is sufficient variation for phylogenetic analy sis, (2) the variation is phylogenetically informative within and betw een some branchiopod orders, and (3) deep-branch phylogenetic resoluti on is limited by saturation effects. Phylogenetic relationships are in ferred by parsimony analysis treating gaps as characters, confidence l imits are estimated by both bootstrapping and the decay index. With a maxillopod sequence (Savignium crenatum) designated as an outgroup, th e following results are obtained: branchiopod orders are monophyletic as sampled in this survey, with the orders Conchostraca and Notostraca clustering as sister taxa. Evidence for lineage specific rate heterog eneity of molecular evolution is discussed.