The changeable relations of the arthropods

A new study comparing the sequences of ADN of 62 genes of 75 species of arthropods (41.000 ADN bases for every species) has revealed several surprises in his familiar tree.

In a work that has extended throughout ten years and with which skills have been refined to extract ADN of the nuclei of the cells, the group of Jerry Regier in the University of Maryland has managed to reconstruct the relations between the arthropods with a grade of detail not known up to the date. Till now, the molecular arthropods filogenia was basing on the comparison of sequences of a few genes nuclerares, mitocondriales and of ARN ribosómico (like, for example, the filogenias of Davide Pisani y Björn M. von Reumont and collaborators of those that I have spoken in Origin and evolution of the artópodos and The origin of the insects or when the crustaceans conquered the ground, but Regier and collaborators have analyzed 41.000 bases of 62 genes in 75 arthropods species, what supposes an enormous work of accused and data analysis.

A new familiar tree. The filogenia of Regier and collaborators confirms that the hexápodos are the terrestrial branch of the crustaceans, places again to the centipedes next to the crustaceans and the hexápodos (Mandibulados) and refines the classification of the crustaceans in three groups: Oligostráceos, Vericrustáceos and Xenocáridos.

To big features, the results can be summed up in the following points:

Pancrustáceos

There is confirmed the crustacean origin of the hexápodos (insects, colémbolos, proturos and dipluros), something at that other molecular filogenias had aimed. Let's remember that that of Pisani was suggesting that the branquiópodos (water fleas, artemias and triops) and the hexápodos were sharing a common ancestor and that of von Reumont was pointing at the common origin of the copépodos and the hexápodos. In case of the filogenia of Regier and collaborators, the hexápodos would share a common origin with the xenocáridos or strange scampi (remípedos and cefalocáridos), group of open crustaceans approximately thirty years ago about which little is known from the genetic point of view and about the development, forming the group Miracrustáceos (surprising crustaceans).

Relations between the crustaceans

Apart from confirming that the crustaceans are not a group monofilético (they do not descend from a common ancestor), they can split into three big groups that comprise a big variety of morphologic features: Oligostracáceos (ostrácodos, mistacocáridos, branquiuros and pentastómidos), Vericrustáceos or real crustaceans (malacostráceos, tecostráceos, copépodos and branquiópodos) and his group I join, Miracrustáceos (xenocáridos and hexápodos).

Mandibulados

The filogenia of Regier and collaborators recovers the subknife-edge Mandibulados (Pancrustáceos and Centipedes), more according to the morphology (crustaceans, hexápodos and centipedes have jaws). The molecular filogenia mitocondrial had suggested, for morfólogos surprise, that the centipedes were closer to the quelicerados (forming the group Paradoxópodos or Mirioquelados).

Paradoxópodos (Mirioquelados) and Mandibulados. Models of the relations between the groups of current arthropods.

Centipedes

According to the Regier filogenia, the centipedes and the pancrustáceos would have a common origin and the relations between the centipedes would not differ much of the filogenias based in morphologic features.

Family portrait. Relation between the centipedes based on morphologic evidences. Adapted of Gregory D. Edgecombe and Gonzalo Giribet, Myriapod Phylogeny and the Relationships of Chilopoda, J. weep to you for Bousquets and J.J. (Eds) Morrone, Biodiversity, Taxonomy and Biogeography of Arthropods of Mexico: Towards a Synthesis of his Knowledge, volume III. Presses of Sciences, Autonomous National University of Mexico (2002), pp. 143-168.

Quelicerados

The quelicerados are a group that it includes to the picnogónidos (chandeliers of sea) and to the euquelicerados (crabs horseshoe and arachnids). The filogenia of Regier and collaborators leaves this group a little in failure, although he confirms that crabs horseshoe and arachnids descend from a common forefather.

Nuclear Arthropod relationships revealed by phylogenomic analysis of protein-coding sequences Jerome C. Regier, Jeffrey W. Shultz, Andreas Zwick, April Hussey, Bernard Ball, Regina Wetzer, Joel W. Martin and Clifford W. Cunningham. 2010. Nature 463, pp. 1079-1083. Regier, J., Shultz, J., Zwick, A., Hussey, A., Ball, B., Wetzer, R., Martin, J., and Cunningham, C. (2010). Nuclear Arthropod relationships revealed by phylogenomic analysis of protein-coding sequences Nature, 463 (7284), 1079-1083 DOI: 10.1038/nature08742 Torrent Brothers & Sisters S04E17 Freeluc.com online