Biology Reference
In-Depth Information
14.3.1 Cold-Temperate Kelps as Biogeographical Models
The large “bull kelp”
Durvillaea
has proved to be an interesting model for seaweed
biogeography. This genus has five recognized species: one (
D. antarctica
)is
buoyant and with circumpolar distribution, while other four are nonbuoyant and
with restricted distribution (
D. willana
present in southern New Zealand,
D. potatorum
in southern Australia and Tasmania,
D. chathamensis
in Chatham
Islands, an undescribed species
Durvillaea
sp. in Antipodes Islands) (Cheshire et al.
1995
) (Fig.
14.3
). Recently, a phylogeographic circum-sub-Antarctic study
provided evidence of recent (postglacial) recolonization by
D. antarctica
, most
probably by transoceanic rafting of adult specimens (see also Chap.
17
by
Rothausler et al.). This is supported by high genetic homogeneity over vast geo-
graphic distances in sub-Antarctic latitudes, while along the coasts of New Zealand
and Chile, substantial genetic differentiation was detected over relatively small
geographic distances (e.g., tens of kilometers) (Fraser et al.
2009b
).
In the coast of Chile, two different lineages of
D. antarctica
with a biogeo-
graphic break at 44-49
S have recently been revealed. Interestingly, populations
from southern Patagonia (49-56
S) were found to be genetically homogenous and
identical to a haplotype found throughout the sub-Antarctic region, pointing to the
transoceanic ancestry and a relative recent recolonization (since the Last Glacial
Maximum) (Fraser et al.
2010a
). Similarly, genetically distinct species have been
postulated for two populations of
D. antarctica
in New Zealand (Fraser et al.
2009c
). Under a phylogenetic species concept, the genus
Durvillaea
has been
recently interpreted as a complex of nine distinct evolutionary lineages, only one
of which has an intercontinental distribution (Fraser et al.
2010b
).
The most widely distributed kelp,
Macrocystis
(Fig.
14.3
), displays an amphi-
equatorial distribution. Four species (
M. pyrifera
,
M., integrifolia
,
M. angustifolia,
and
M. laevis
) are currently recognized, however, increasing evidence strongly
suggests the existence of a single morphologically plastic species (reviewed by
Graham et al.
2007
; Demes et al.
2009
). Phylogenetic analyses by Coyer et al.
(
2001
) point to a very recent (0.01-3 Ma) dispersal of
Macrocystis
from the
northern to the southern hemisphere. This direction of the dispersal was supported
by the greater genetic diversity of the individuals of the northern hemisphere,
displaying paraphyletic clades, while the southern individuals formed monophy-
letic clades and showed little genetic differentiation across a wide southern geo-
graphic range, which refers to a recent dispersal.
Unlike the floating
D. antarctica
, the species of the genus
Lessonia
show a
disperse distribution along the southern hemisphere (Fig.
14.3
) characterized by a
remarkable regional endemism (Searles
1978
). The only intertidal species,
L. nigrescens
, extends from 17
Sto56
S and is the dominant organism at the
infralittoral zone of the wave exposed locations of Chile and Peru (Santelices
1989
). The subtidal
L. trabeculata
has a distribution range from 12 to 41
S in the
eastern Pacific coast (from Peru to Chilo´ Island) (Villouta and Santelices
1986
).
Populations of
L. vadosa
are found in the southern South America (47-56
S) in the
