Comparison of articulate brachiopod nuclear and mitochondrial gene trees leads to a clade–based redefinition of protostomes (Protostomozoa) and deuterostomes (Deuterostomozoa)

Abstract

Nuclear and mtDNA sequences from selected short-looped terebratuloid (terebratulacean) articulate brachiopods yield congruent and genetically independent phylogenetic reconstructions by parsimony, neighbour-joining and maximum likelihood methods, suggesting that both sources of data are reliable guides to brachiopod species phylogeny. The present-day genealogical relationships and geographical distributions of the tested terebratuloid brachiopods are consistent with a tethyan dispersal and subsequent radiation. Concordance of nuclear and mitochondrial gene phylogenies reinforces previous indications that articulate brachiopods, inarticulate brachiopods, phoronids and ectoprocts cluster with other organisms generally regarded as protostomes. Since ontogeny and morphology in brachiopods, ectoprocts and phoronids depart in important respects from those features supposedly diagnostic of protostomes, this demonstrates that the operational de¢nition of protostomy by the usual ontological characters must be misleading or unreliable. New, molecular, operational de¢nitions are proposed to replace the traditional criteria for the recognition of protostomes and deuterostomes, and the clade-based terms Protostomozoa' and`Deuterostomozoa' are proposed to replace the existing terms`Protostomia' and Deuterostomia'.

DNA sequence evidence for speciation, paraphyly and a Mesozoic dispersal of cancellothyridid articulate brachiopods

“…16S rates are ~1.4 times 12S rates). Thus, both comparisons indicate that the brachiopod sequences described here may evolve slowly, in keeping with the unusually deep phylogenetic resolution obtained from brachiopod 12S sequences (Cohen et al 1998c). …”

“…In other previous work, analyses of an alignment of 12S rDNAs from a wide taxonomic range of shortlooped brachiopods including cancellothyridids gave evidence of strong phylogenetic signal and stationary base composition (Cohen et al 1998c). In the new 12S alignment described here, phylogenetic signal was high (g1 from 10,000 random trees and 80 informative characters = -0.86, P < 0.01, Hillis and Huelsenbeck 1992) and base composition again showed no heterogeneity (P = 1.00, 84 d. f.).…”

“…The starting-point for the present work was an earlier 12S alignment (EMBL DS32096, Cohen et al 1998c) To this were added a sequence from Terebratulina crossei and 19 more sequences from North Atlantic Terebratulina spp., whilst sequences of all other taxa except the short-looped brachiopods Liothyrella spp. were removed.…”

“…Some members of this family fall into a wellsupported molecular clade (Cohen et al 1998a;Cohen et al 1998c;Cohen 2001). …”

The evolution of the serotonergic nervous system

“…However, there are other signi¢cant di¡er-ences between phoronids, brachiopods and the spiralian protostome phyla based on the structure of the larval serotonergic nervous system. The type 5 system de¢nes a pattern which obviously groups the phoronids and brachiopods with the deuterostomes and is thus just one more character where anatomical data di¡er from 18S rDNA sequence data (Nielsen 1995;Cohen et al 1998). Recently, Zrzavy et al (1998) concluded that the a¤lia-tion of the brachiopods and phoronids to the spiralian phyla based on rDNA sequences is an out-group artefact and may not re£ect a real relationship.…”