EVOLUTION OF THE FUCACEAE (PHAEOPHYCEAE) INFERRED FROM nrDNA‐ITS

Abstract

Sequences of the internal transcribed spacer region (ITS-1, 5.8S, and ITS-2) of nuclear ribosomal DNA were obtained from 16 species representing all six genera of Fucaceae (Ascophyllum, Fucus, Hesperophycus, Pelvetia, Pelvetiopsis, and Xiphophora) plus one outgroup (Hormosira). Parsimony analysis indicated that the family Fucaceae is monophyletic and that the northern hemisphere taxa are highly divergent from the only southern hemisphere genus, Xiphophora. The genus Pelvetia is not monophyletic because the European P. canaliculata is more closely related to Fucus, Hesperophycus, and Pelvetiopsis than to other Pelvetia species. We establish Silvetia, gen. nov. and transfer the 3 Pacific species of Pelvetia to the new genus. Fucus is monophyletic and not ancestral in the Fucaceae. The ITS sequences identified two strongly supported lineages within Fucus, one with F. serratus sister to the clade containing F. gardneri, F. distichus, and F. evanescens and a second including F. vesiculosus, F. spiralis, F. ceranoides, and F. virsoides. The ITS was not useful for resolving relationships within each of these clusters and between populations of F. vesiculosus. Within-individual variation in ITS sequences is high in Fucus, a derived genus, compared to Ascophyllum, a more ancestral genus. Mapping of the two characters that form the basis of Powell's model for speciation in the Fucaceae showed that 1) number of eggs per oogonium has not followed a gradual reduction and that 2) monoecy/dioecy has changed several times during evolution of this family.

Evolution and diversification within the intertidal brown macroalgae Fucus spiralis/F. vesiculosus species complex in the North Atlantic

“…The presence of a unique haplotype in the single Pacific population that was shared with Atlantic populations supports the hypothesis of a recent introduction of the Pacific by F. spiralis (see also Lüning, 1990;Serrão et al, 1999;Coyer et al, 2006a). The restriction of populations to the Washington State (USA)-British Columbia (Canada) border (as opposed to distribution throughout the North Pacific) further supports the introduction hypothesis (see Coyer et al, 2006a, and references therein).…”

“…It is likely that the Fucus lineage comprised of these species (Lineage 2) (Serrão et al, 1999;Coyer et al, 2006a) arose and diverged in the North Atlantic, rather than the North Pacific where none of the species occurs naturally (F. spiralis is an introduction, see below).…”

“…Lineage 1 consists of Fucus serratus and Fucus distichus sensu lato and Lineage 2 of Fucus vesiculosus, Fucus spiralis, F. radicans, Fucus ceranoides, and Fucus virsoides (Serrão et al, 1999;Coyer et al, 2006a). From a morphological standpoint, over 125 intraspecific taxa have been described for the nine most common species (Guiry and Guiry, 2010).…”

Fucus vesiculosus and spiralis species complex: a nested model of local adaptation at the shore level

“…In this section, we discuss whether the shared genetic variation between the different Fucus clusters is simply a remnant of ancestral variation or if it is due to gene exchange after the populations started to separate. It is now widely accepted that species in the Fucus genus experienced recent radiation (Leclerc et al 1998, Serrão et al 1999, Coyer et al 2006. In recent studies, authors have tried to date these splitting events; by inferring a molecular clock, Hoarau et al (2007) recently suggested a divergence time of 10 to 16 million yr between Fucus and Ascophyllum nodosum and of 2.3 to 5.5 million yr within Fucus and Muhlin & Brawley (2009), using the same molecular clock, dated the divergence between haplotypes of F. vesiculosus between 35 000 and 65 000 yr ago, while with microsatellites, Pereyra et al (2009) estimated the time since divergence of F. radicans and F. vesiculosus around 400 yr ago (125 to 2475 yr ago) using a coalescent approach.…”

“…Fucus species are genetically very closely related, and all phylogenetic studies (Leclerc et al 1998, Serrão et al 1999, Coyer et al 2006) suggest a recent and rapid radiation. The genus Fucus consists of 2 clades, the first containing F. vesiculosus and F. spiralis, and a second that includes F. serratus, which are the dominant Fucus species found on open-coast rocky shores of the European eastern Atlantic.…”