Molecular phylogenies confirm the presence of two cryptic Hemimycale species in the Mediterranean and reveal the polyphyly of the genera Crella and Hemimycale (Demospongiae: Poecilosclerida)
Este artículo contiene 24 páginas, 4 figuras, 3 tablas.Background: Sponges are particularly prone to hiding cryptic species as their
paradigmatic plasticity often favors species phenotypic convergence as a result of
adaptation to similar habitat conditions. Hemimycale is a sponge genus (Family
Hymedesmiidae, Order Poecilosclerida) with four formally described species, from
which only Hemimycale columella has been recorded in the Atlanto-Mediterranean
basin, on shallow to 80 m deep bottoms. Contrasting biological features between
shallow and deep individuals of Hemimycale columella suggested larger genetic
differences than those expected between sponge populations. To assess whether
shallow and deep populations indeed belong to different species, we performed a
phylogenetic study of Hemimycale columella across the Mediterranean. We
also included other Hemimycale and Crella species from the Red Sea, with the
additional aim of clarifying the relationships of the genus Hemimycale.
Methods: Hemimycale columella was sampled across the Mediterranean, and
Adriatic Seas. Hemimycale arabica and Crella cyathophora were collected from
the Red Sea and Pacific. From two to three specimens per species and locality
were extracted, amplified for Cytochrome C Oxidase I (COI) (M1–M6 partition),
18S rRNA, and 28S (D3–D5 partition) and sequenced. Sequences were aligned using
Clustal W v.1.81. Phylogenetic trees were constructed under neighbor joining (NJ),
Bayesian inference (BI), and maximum likelihood (ML) criteria as implemented in
Geneious software 9.01. Moreover, spicules of the target species were observed
through a Scanning Electron microscope.
Results: The several phylogenetic reconstructions retrieved both Crella and
Hemimycale polyphyletic. Strong differences in COI sequences indicated that
C. cyathophora from the Red Sea might belong in a different genus, closer to
Hemimycale arabica than to the Atlanto-Mediterranean Crella spp. Molecular and
external morphological differences between Hemimycale arabica and the Atlanto-
Mediterranean Hemimycale also suggest that Hemimycale arabica fit in a separate
genus. On the other hand, the Atlanto-Mediterranean Crellidae appeared in 18S
and 28S phylogenies as a sister group of the Atlanto-Mediterranean Hemimycale.
Moreover, what was known up to now as Hemimycale columella, is formed by two cryptic species with contrasting bathymetric distributions. Some small
but consistent morphological differences allow species distinction.
Conclusions: A new family (Hemimycalidae) including the genus Hemimycale and
the two purported new genera receiving C. cyathophora and Hemimycale arabica
might be proposed according to our phylogenetic results. However, the inclusion
of additional Operational Taxonomic Unit (OTUs) appears convenient before taking
definite taxonomical decisions. A new cryptic species (Hemimycale mediterranea
sp. nov.) is described. Morphologically undifferentiated species with contrasting
biological traits, as those here reported, confirm that unidentified cryptic species
may confound ecological studies.The research has been funded by MARSYMBIOMICS project (Spanish MINECO,
CTM2013-43287-P), BluePharmTrain (FP7 People-INT, Ref. 2013-667786), and Grup
Consolidat SGR-120, to Maria J. Uriz. Leire Garate benefited from a fellowship within
the Benthomics project (Spanish MICINN, CTM-2010-22218-C02-01).Peer reviewe