Phylogenetic relationships of extant echinoderm classes1
نویسنده
چکیده
A well-supported phylogeny of echinoderm classes has eluded morphological, embryological, molecular, and combined analyses. From this body of work it is apparent that (i) echinoids (sea urchins) and holothuroids (sea cucumbers) are related, and (ii) crinoids (sea lilies) are the sister taxon to extant eleutherozoan classes (asteroids, ophiuroids, echinoids, and holothuroids). However, the relationships of asteroids and ophiuroids to other echinoderm classes have been difficult to recover. To address relationships between the asteroids and ophiuroids and other echinoderms, I have sequenced additional nuclear loci and taxa and used novel computational approaches for co-optimizing morphological with molecular evidence at the level of sequence alignment. Support for the monophyly of each class is strong. Support for a monophyletic Asteroidea + Xyloplax is as strong as for Asteroidea. Support for Asterozoa (Asteroidea + Ophiuroidea) is apparent, albeit not as strong as for other clades (e.g., Echinozoa, Eleutherozoa, and Echinodermata). I also present detailed sensitivity analyses to provide (i) a test of the monophyly of groups under a variety of evolutionary models and (ii) a statement of the evidential value of various character systems. Résumé : Les analyses morphologiques, embryologiques, moléculaires et combinée n’ont pas encore permis d’établir une phylogénie solide des classes d’échinodermes. D’après le bilan de ces travaux, il est évident que (i) les échinoïdes (oursins de mer) et les holothuroïdes (concombres de mer) sont des groupes apparentés et (ii) que les crinoïdes (lys de mer) forment le taxon soeur des classes d’éleuthérozoaires actuels (astéroïdes, ophuroïdes, échinoïdes et holothuroïdes). Cependant, la relation entre les astéroïdes et les ophiuroïdes et les autres classes d’échinodermes est difficile à établir. Pour examiner cette relation, j’ai procédé au séquençage de nouveaux locus nucléaires et examiné d’autres taxons et j’ai utilisé de nouvelles approches informatiques pour cooptimiser les données morphologiques et moléculaires à l’alignement des séquences. Tous les indices appuient l’hypothèse du monophylétisme de chacune des classes. Le monophylétisme des Asteroidea + Xyloplax est aussi corroboré que celui des Asteroidea. L’appuie en faveur des Asterozoa (Asteroidea + Ophiuroidea) est également corroboré, mais pas aussi fortement que pour les autres clades (p. ex., Echinozoa, Eleutherozoa et Echinodermata). Je présente également ici des analyses détaillées de sensibilité : (i) un test du monophylétisme des groupes à la lumière de plusieurs modèles évolutifs et (ii) un jugement sur la valeur indicatrice de différents systèmes de caractères. [Traduit par la Rédaction] Reviews / Synthèses 1250
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