Molecular data suggest a hybrid origin for the invasiveCaulerpa racemosa(Caulerpales, Chlorophyta) in the Mediterranean Sea

Abstract

Morphological data has provided a basis for the hypothesis that three taxa belonging to the Caulerpa racemosa complex occur in the Mediterranean Sea: var. turbinata–uvifera, var. lamourouxi, and the `invasive variety'. In order to test this hypothesis and to determine the origin of the `invasive variety', the transcribed spacer ITS1–ITS2 and an 18S ribosomal DNA (rDNA) intron were analysed from 16 isolates of Caulerpa racemosa. The `invasive variety' shows intraindividual polymorphism for both types of sequences. The ITS1–ITS2 data confirm that the three morphological varieties of C. racemosa from the Mediterranean Sea are distinct taxonomic units. The 18S intron data suggest that the new `invasive variety' could be a recent hybrid between var. turbinata–uvifera and an unknown tropical strain. Incongruence between the phylogenetic tree computed from ITS1–ITS2 regions and the 18S intron indicates that homogenization processes of concerted evolution have run at different rates.

Molecular systematics, historical ecology, and phylogeography of Halimeda (Bryopsidales)

“…The identical location of the SSU insert in all tested representatives across Halimedineae and Caulerpaceae (this study, Durand et al, 2002;Hillis et al, 1998;Kooistra, 2002;Kooistra et al, 1999) indicates its conserved existence. Its relatively slow substitution rate in comparison to the ITS regions, conserved length, similar secondary structure, and high CG% in Halimeda suggest functionality in the mature ribosome and the existence of a novel conserved region in the SSU.…”

“…Therefore, we could combine the various nrDNA regions in a single phylogenetic analysis. Such is not always appropriate, e.g., when different sequence regions produce conflicting phylogenies (Durand et al, 2002). In Caulerpa racemosa, Fama a et al (2000) and Durand et al (2002) revealed considerable intra-individual ITS sequence variation and the latter authors also showed conflict between trees inferred from the insert and ones from the ITS regions, all suggestive of hybridization events.…”

“…Such is not always appropriate, e.g., when different sequence regions produce conflicting phylogenies (Durand et al, 2002). In Caulerpa racemosa, Fama a et al (2000) and Durand et al (2002) revealed considerable intra-individual ITS sequence variation and the latter authors also showed conflict between trees inferred from the insert and ones from the ITS regions, all suggestive of hybridization events. Ribosomal RNA coding regions are particularly prone to introgression (Nichols, 2001;Riseberg and Wendel, 1993;Sang et al, 1995;Wendel et al, 1995) because of their multi-copy nature (Jorgensen and Cluster, 1988).…”

“…Many authors have used nuclear rDNA (nrDNA) sequences for phylogenetic inferences in green algae (Bakker et al, 1994(Bakker et al, , 1995a(Bakker et al, , 1995bColeman and Mai, 1997;Durand et al, 2002;Fama a et al, 2000;Jousson et al, 1998;Nakayama et al, 1998;Olsen et al, 1994Olsen et al, , 1998. Different mutation rates among nrDNA regions permit phylogenetic resolution at several taxonomic levels (Jorgensen and Cluster, 1988).…”

A multi-locus time-calibrated phylogeny of the siphonous green algae

“…Alignment of 18S rDNA sequences followed an analogous procedure. The insert near the 3 0 terminus of the 18S gene of certain Bryopsidales (Durand et al, 2002;Hillis et al, 1998;Kooistra et al, 1999) was removed because it was not present in all taxa and virtually impossible to align among genera. After removal of this region, sequences were aligned with Muscle v. 3.6 and stripped of their ambiguous regions.…”