Research Summary: Molecular Phylogeny of the Astrophorida (Porifera, Demospongiaep) Reveals an Unexpected High Level of Spicule Homoplasy

ABSTRACT

Background

The Astrophorida (Porifera, Demospongiaep) is
geographically and bathymetrically widely distributed. Systema
Porifera
currently includes five families in this order:
Ancorinidae, Calthropellidae, Geodiidae, Pachastrellidae and Thrombidae. To
date, molecular phylogenetic studies including Astrophorida species are
scarce and offer limited sampling. Phylogenetic relationships within this
order are therefore for the most part unknown and hypotheses based on
morphology largely untested. Astrophorida taxa have very diverse spicule
sets that make them a model of choice to investigate spicule evolution.


Methodology/Principal Findings

With a sampling of 153 specimens (9 families, 29 genera, 89 species) covering
the deep- and shallow-waters worldwide, this work presents the first
comprehensive molecular phylogeny of the Astrophorida, using a cytochrome
c oxidase subunit I (COI) gene partial sequence and the
5′ end terminal part of the 28S rDNA gene (C1-D2 domains). The
resulting tree suggested that i) the Astrophorida included some lithistid
families and some Alectonidae species, ii) the sub-orders Euastrophorida and
Streptosclerophorida were both polyphyletic, iii) the Geodiidae, the
Ancorinidae and the Pachastrellidae were not monophyletic, iv) the
Calthropellidae was part of the Geodiidae clade
(Calthropella at least), and finally that v) many
genera were polyphyletic (Ecionemia,
Erylus, Poecillastra,
Penares, Rhabdastrella,
Stelletta and Vulcanella).


Conclusion

The Astrophorida is a larger order than previously considered, comprising ca.
820 species. Based on these results, we propose new classifications for the
Astrophorida using both the classical rank-based nomenclature (i.e.,
Linnaean classification) and the phylogenetic nomenclature following the
PhyloCode, independent of taxonomic rank. A key to the
Astrophorida families, sub-families and genera incertae
sedis
is also included. Incongruences between our molecular
tree and the current classification can be explained by the banality of
convergent evolution and secondary loss in spicule evolution. These
processes have taken place many times, in all the major clades, for
megascleres and microscleres.

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Publisher: Public Library of Science

Date Published: 8-April-2011

Author(s): Cárdenas P., Xavier J., Reveillaud J., Schander C., Rapp H.

Link: https://doi.org/10.1371/journal.pone.0018318

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