Biology Reference
In-Depth Information
12.3.3 Case Study:
Undaria Pinnatifida
The brown seaweed
Undaria pinnatifida
, known as the edible
wakame
(Fig.
12.2b
),
was originally endemic to Japan, Korea, and China where it is industrially cultivated.
Firstly observed outside its native distribution range in the Mediterranean Sea (Etang
de Thau, French, 1970s) the species has in few years invaded many of the world's
oceans from Europe to North America, Australasia, and New Zealand; both by
accidental translocation via oyster farming from Japan and intentional introduction
for cultivation purposes (Voisin et al.
2005
). It was possible to explore and elucidate
the invasion history of this species by means of sequence analysis of the mitochon-
drial
atp
8-
trn
Sand
trn
W-
trn
I intergenic spacers, the partial
cox
3 gene and the
tatC-
tLeu
gene regions. The latter DNA loci revealed highly differentiated populations,
each characterized by low levels of haplotype diversity in the native geographical
range of the species (Voisin et al.
2005
). On the contrary, where
U. pinnatifida
has
been introduced, populations were found to be highly diverse. The so distributed
genetic diversity clearly indicated that introduced populations of
U. pinnatifida
are
the results of multiple introduction events from more than one native population.
Furthermore, the difference in haplotype diversity found in introduced populations
sampled from Europe and Australasia indicated differences in the dynamics of the
colonization process (Voisin et al.
2005
;Uwaietal.
2006a
,
b
).
12.3.4 Case Study:
Asparagopsis Armata
The red seaweed
Asparagopsis armata
Harvey (Fig.
12.3a
) is a genetically homoge-
neous species originally described from Southern Australia, Tasmania, and New
Zealand and first reported in the northern hemisphere from Algeria in 1925 (Horridge
1951
). Molecular phylogenies inferred from the D1, D2, and D3 hyper-variable
domains of the nuclear large subunit rDNA gene the plastid RUBISCO spacer and
the mitochondrial cox2-3 intergenic spacer indicated just a single plastid haplotype
distributed worldwide and a limited number of panmictic nuclear and mitochondrial
haplotypes in presumably native and introduced populations.
Asparagopsis armata
exhibits great dispersal potential due to a free-floating tetrasporophyte in its life cycle
(see below) and propagation via fragmentation and attachment to other floating
structures and has always been reported as a recently introduced, potentially invasive,
species from the Mediterranean Sea and western European coasts. Given the
complete absence of phylogeographic structuring on global and local scales and
the inadequate phylogenetic signal of nuclear, mitochondrial, and plastid markers,
only general assumptions on the origins of introduced populations and the
direction of the spread can be made. Furthermore, significant taxonomic confusion
surrounds this species and has been propagated since its first description. This
is because no diagnostic morphological characters are known to differentiate between
tetrasporophytes (the “
Falkenbergia
” stage, previously described as separate species)
