Reconstruction of family-level phylogenetic relationships within Demospongiae (Porifera) using nuclear encoded housekeeping genes.
BACKGROUND
Demosponges are challenging for phylogenetic systematics because of their plastic and relatively simple morphologies and many deep divergences between major clades. To improve understanding of the phylogenetic relationships within Demospongiae, we sequenced and analyzed seven nuclear housekeeping genes involved in a variety of cellular functions from a diverse group of sponges.


RESULTS
We generated data from each of the four sponge classes (i.e., Calcarea, Demospongiae, Hexactinellida, and Homoscleromorpha), but focused on family-level relationships within demosponges. With data for 21 newly sampled families, our Maximum Likelihood and Bayesian-based approaches recovered previously phylogenetically defined taxa: Keratosa(p), Myxospongiae(p), Spongillida(p), Haploscleromorpha(p) (the marine haplosclerids) and Democlavia(p). We found conflicting results concerning the relationships of Keratosa(p) and Myxospongiae(p) to the remaining demosponges, but our results strongly supported a clade of Haploscleromorpha(p)+Spongillida(p)+Democlavia(p). In contrast to hypotheses based on mitochondrial genome and ribosomal data, nuclear housekeeping gene data suggested that freshwater sponges (Spongillida(p)) are sister to Haploscleromorpha(p) rather than part of Democlavia(p). Within Keratosa(p), we found equivocal results as to the monophyly of Dictyoceratida. Within Myxospongiae(p), Chondrosida and Verongida were monophyletic. A well-supported clade within Democlavia(p), Tetractinellida(p), composed of all sampled members of Astrophorina and Spirophorina (including the only lithistid in our analysis), was consistently revealed as the sister group to all other members of Democlavia(p). Within Tetractinellida(p), we did not recover monophyletic Astrophorina or Spirophorina. Our results also reaffirmed the monophyly of order Poecilosclerida (excluding Desmacellidae and Raspailiidae), and polyphyly of Hadromerida and Halichondrida.


CONCLUSIONS
These results, using an independent nuclear gene set, confirmed many hypotheses based on ribosomal and/or mitochondrial genes, and they also identified clades with low statistical support or clades that conflicted with traditional morphological classification. Our results will serve as a basis for future exploration of these outstanding questions using more taxon- and gene-rich datasets.
Gottwald Science Center, University of Richmond, Richmond, Virginia, United States of America.
Malcolm S
MS
Hill
April L
AL
Hill
Jose
J
Lopez
Kevin J
KJ
Peterson
Shirley
S
Pomponi
Maria C
MC
Diaz
Robert W
RW
Thacker
Maja
M
Adamska
Nicole
N
Boury-Esnault
Paco
P
Cárdenas
Andia
A
Chaves-Fonnegra
Elizabeth
E
Danka
Bre-Onna
BO
De Laine
Dawn
D
Formica
Eduardo
E
Hajdu
Gisele
G
Lobo-Hajdu
Sarah
S
Klontz
Christine C
CC
Morrow
Jignasa
J
Patel
Bernard
B
Picton
Davide
D
Pisani
Deborah
D
Pohlmann
Niamh E
NE
Redmond
John
J
Reed
Stacy
S
Richey
Ana
A
Riesgo
Ewelina
E
Rubin
Zach
Z
Russell
Klaus
K
Rützler
Erik A
EA
Sperling
Michael
M
di Stefano
James E
JE
Tarver
Allen G
AG
Collins
D000818:Animals; D002467:Cell Nucleus / Q000737:chemistry / Q000235:genetics*; D004275:DNA, Ribosomal / Q000145:classification / Q000235:genetics; D019143:Evolution, Molecular; D020043:Genes, Essential; D050259:Genes, Mitochondrial; D008957:Models, Genetic; D010802:Phylogeny; D011161:Porifera / Q000145:classification* / Q000235:genetics*; D017422:Sequence Analysis, DNA
D004275:DNA, Ribosomal