Biology Reference
In-Depth Information
coasts of Chile and Argentina as well as in the Falkland Islands (Searles
1978
;
Scrosati
1991
).
L. flavicans
has also been described for South Georgia (John et al.
1994
).
L. variegata
is endemic to New Zealand region including the mainland
(Schwarz et al.
2006
) and some adjacent islands (Chatham, Auckland, and
Macquarie) (Kenny and Haysom
1962
; Hay
1981
). Other species show restricted
distribution in this region,
L. tholiformis
being
e
ndemic to Chatham Island (Hay
1989
),
L. brevifolia
present in Auckland, Campbell, Antipodes, and Bounty Islands
(Hay
1981
,
1987
),
L. adamsiae
in Snares Islands (Hay
1987
), and
L. corrugata
in
Tasmania (Lane et al.
2006
) (Fig.
14.3
).
Recent phylogeographic analyses indicated the presence of two main divergent
lineages, possibly two cryptic species, within
L. nigrescens
of the coast of Chile
(Tellier et al.
2009
), which matches the biogeographical transition zone around
30
S. In this species complex, a very limited dispersal has been reported (Faugeron
et al.
2005
; Tellier et al.
2009
), confirming the marked endemism in many regions.
Apparently, environmental factors (e.g., temperature) and anthropogenic activities
can reduce gene flow between populations of
L. nigrescens
(Faugeron et al.
2005
;
Oppliger et al.
2011
). Despite some molecular analyses (Lane et al.
2006
), the
origin of the genus
Lessonia
still remains unclear. Interestingly, within
Lessoniaceae, it is the only genus not present in the northern hemisphere, and
furthermore, it does not appear to be closely related to the other genera of this
family (Bolton
2010
).
14.4 Major Differences with Cold Temperate Regions
of the Northern Hemisphere
Cold-adapted seaweeds are believed to have developed during the Tertiary decline
of seawater temperature in temperate and polar regions. A permanent separation of
the southern and northern hemisphere cold-water flora was produced by the forma-
tion of the pan-tropical Tethys Sea during the Mezozoic era (251-65 Ma). The
presence of amphi-equatorial species with cold-temperate characteristics might be
the result of processes such as paleoclimatic vicariance during the Miocene when
intrusion of glacial water masses allowed many species crossing the equator
(L
uning
1990
; see also Chap.
18
by Bartsch et al.). However, some evidence
indicates that disjunctions for some species are of a recent origin, e.g., during the
last Pleistocene glacial maximum (18,000 years ago) (van Oppen et al.
1994
). In the
genus
Macrocystis
, phylogenetic analyses point to a very recent (0.01-3 Ma)
dispersal from the northern to the southern hemisphere (Coyer et al.
2001
). These
transequatorial migrations took place at the east side of the oceans where the
tropical regions are compressed. Crossing the equator was facilitated by “stepping
stones,” as well as by further constriction of the tropical regions during the
Pleistocene and by glacial temperature drops as high as 8
C (reviewed by L
€
uning
€
1990
; see also Chap.
18
by Bartsch et al.).
