Dyctiota

J. Phycol. 46, ***–*** (2010)
Ó 2010 Phycological Society of America
DOI: 10.1111/j.1529-8817.2010.00908.x

S PECIES DELIMITATION, TAXONOMY, AND BIOGEOGRAPHY OF DICTYOTA
IN EUROPE (DICTYOTALES, PHAEOPHYCEAE) 1
Ana Tronholm2
Departamento de Biologıa Vegetal (Botanica), Universidad de La Laguna,
´
´
38271 La Laguna, Canary Islands, Spain

Frederique Steen, Lennert Tyberghein, FrederikLeliaert, Heroen Verbruggen
Phycology Research Group and Centre for Molecular Phylogenetics and Evolution, Ghent University,
Krijgslaan 281, Building S8, 9000 Ghent, Belgium

M. Antonia Ribera Siguan
Unitat de Botanica, Facultat de Farmacia, Universitat de Barcelona, Joan XXIII s ⁄ n,
`
`
08032 Barcelona, Spain

and Olivier De Clerck
Phycology Research Group and Centre for MolecularPhylogenetics and Evolution,
Ghent University, Krijgslaan 281, Building S8, 9000 Ghent, Belgium

Taxonomy of the brown algal genus Dictyota has a
long and troubled history. Our inability to distinguish morphological plasticity from fixed diagnostic
traits that separate the various species has severely
confounded species delineation. From continental
Europe, more than 60 species and intraspecifictaxa
have been described over the last two centuries.
Using a molecular approach, we addressed the
diversity of the genus in European waters and made
necessary taxonomic changes. A densely sampled
DNA data set demonstrated the presence of six evolutionarily significant units (ESUs): Dictyota dichotoma
(Huds.) J. V. Lamour., D. fasciola (Roth) J. V.
Lamour., D. implexa J. V. Lamour., D.mediterranea
(Schiffn.) G. Furnari, D. spiralis Mont., and the
newly described D. cyanoloma sp. nov., which was
previously reported as D. ciliolata from the Mediterranean Sea. Species distributions, based on
DNA-confirmed occurrence records, indicate that all
species are geographically confined to the NE
Atlantic Ocean with the exception of D. dichotoma
and D. implexa, which also occur in SouthAfrica
and Bermuda, respectively. To investigate potential
hybridization between D. dichotoma and D. implexa,
which were previously shown to be sexually compatible in culture, we compiled and analyzed sets of
mitochondrial, plastid, and nuclear markers to
detect putative hybrids or introgression in natural
populations. Failure to detect natural hybrids indicates that effective pre- andpostzygotic isolation
mechanisms are at play in natural populations and

supports the by-product hypothesis of reproductive
isolation.
Key index words: biogeography; Dictyota ; Dictyotales;
diversity; molecular phylogenetics; taxonomy
Abbreviations: AIC, Akaike information criterion;
BI, Bayesian inference; BIC, Bayesian information
criterion; GTR, general time reversible; ML,
maximumlikelihood

Species of the genus Dictyota J. V. Lamour., along
with other Dictyotales, are key components of many
coastal ecosystems (Luning 1990). Due to their efެ
cient chemical defense systems, which involve
various diterpenes as well as gaseous volatiles (Hay
et al. 1987, Wiesemeier et al. 2007), and their ability
to propagate successfully by fragmentation (Herren
et al. 2006), the speciesare able to maintain a significant biomass under high grazing pressure and
therefore have an important role in the structuring
of benthic communities in tropical and temperate
ecosystems. Despite their prevalence and ecological
importance, species-level taxonomy is long and troubled.
Species are routinely used as fundamental units
of ecological surveys, conservation biology, biogeography, andmacroevolution, yet the empirical delimitation of species can pose serious difficulties (Wiens
1999, Agapow et al. 2004, Sites and Marshall 2004).
Defining species boundaries is inherently linked to
the species concept applied. Despite extensive disputes over species concepts, most biologists agree
that species are lineages, and what previous authors

1

Received 13 January 2010. Accepted...