A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...

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CHAPTER TEN
DISCUSSION
10.1 SPECIATION
~~ree
of the four. DurviZlaea species are endemic to either
Soutlleast Australia, New Zealand or Chatham and Antipodes Islands,
suggesting that speciation is centred in the e~treme southwest
Pacific region. These three: D. potatorum, D. wiUana and D.
chathamica are probably the result of allopatric speciation. With noobuoyant
blades they cannot drift across the Tasman Sea or between New
Zealand and the Chatham-Antipodes region, and are therefore geographically
isolated. D. antaY'ctica, the only species with buoyant
blades, is capable of drifting vast distances and is distributed around
the southern hemisphere.
Many D. anta:rotica populations are widely separated, either by
sea or by long expanses of beach. Although plants drift vast
distances (see Appendix 4) it is unlikely that the gene pools of
widely separated populations are completely integrated. Slight
morphological differences between populations are to be expected.
This explains why the stipes of D. antarctica in the southern half of
the South Island often branch distally (Fig, 5.l1a,b) whereas this
feature is absent in Northland populations, and why only D. antarctica
from the isolated Chatham Islands have lateral thongs growing from
their stipes (Fig_ S.lle-f). Closer investigation of D. ~~tarctioa
populations on southern islands will undoubtedly reveal minor
morphological features peculiar to individual island populations.
It is interesting to speculate what the evolutiDnary history of
the four DurviZlaea species may have been. The genus contains a
mixture of fucalean and laminarian features, and it is possible that
it evolved from a stock
of: plants similar to that of thG
antarctic kelp Ascoseira miY'abiZis Skottsbg. which superficially
resembles a small D. m~tarctica or D. ohabhamioa plant. According to
Skottsberg (1921:50) it has asol:id hoof-like holdfast, a short stout
stipe and a variably divided blade with conceptacles 0)1 both surfaces"
It differs from Durvillaea in that its conceptacles contain chains of
r-eproductive Ol':gans each containing eight reprodu.ctive cells (spores?)