306
o. Clement et aI.
The neighbour - joining tree and the Dollo parsimony trees are
congruent, though the maximum parsimony trees do not solve the
relations between the taxa Chionodraco hamatus, Chionodraco
rastrospinosus and Chaenodraco wilsoni.
The most important results, in agreement in the two kinds of trees, are
(1) the basal topology (Champsocephalus (Neopagetopsis (Pagetopsis, the
rest))) found by the two methods; (2) the paraphyly of the genus
Chionodraco and (3) the terminal clade (Channichthys (Chaenocephalus,
Cryodraco )).
Discussion and Conclusions
Long Distance Differentiation
Based on the significant Fst, two species present a pattern of isolation by
distance. Chionodraco myersi and Neopagetopsis ionah are the two first
Antarctic species showing genetic divergence between two geographic
areas, the Weddell Sea and Prydz Bay. Even if the observation is limited
to two sites, it is new. Mitochondrial DNA analyses [15] and allozymic
surveys [6] did not give such results.
One can notice that the significant long distance divergence was
observed only in those species with good sample size. It is probable that if
all species analyzed here had been represented by larger samples, more
than two cases of differentiation would be described. On the other hand,
Champsocephalus gunnari was not structured with sufficiently large
samples in the three populations analyzed [6]. It is possible that Antarctic
species are more structured due to local isolation than subAntarctic
species as observed from chromosomal data (unpublished).
Structure of Chionodraco myersi populations in the Weddell Sea
Among the four populations considered, three are located in Weddell Sea.
Among them, two (no. 6 and 8) are precisely located near Norvegia Cape,
and the other in Halley Bay. The population 7 remains different from the
two others. The physicochemical characteristics of that station [16] cannot
explain the structure. Nevertheless, the Norvegia Cape, at the level of the
slope break in the continental sh~lf, presents a rapid geotrophic stream
running to the South (20 cm sec ). That peculiarity could provoke the
isolation from the population 7. Thus there could not be any larval
mixture due to the pelagic fry often permitting gene flow.
o. Clement et aI.
The neighbour - joining tree and the Dollo parsimony trees are
congruent, though the maximum parsimony trees do not solve the
relations between the taxa Chionodraco hamatus, Chionodraco
rastrospinosus and Chaenodraco wilsoni.
The most important results, in agreement in the two kinds of trees, are
(1) the basal topology (Champsocephalus (Neopagetopsis (Pagetopsis, the
rest))) found by the two methods; (2) the paraphyly of the genus
Chionodraco and (3) the terminal clade (Channichthys (Chaenocephalus,
Cryodraco )).
Discussion and Conclusions
Long Distance Differentiation
Based on the significant Fst, two species present a pattern of isolation by
distance. Chionodraco myersi and Neopagetopsis ionah are the two first
Antarctic species showing genetic divergence between two geographic
areas, the Weddell Sea and Prydz Bay. Even if the observation is limited
to two sites, it is new. Mitochondrial DNA analyses [15] and allozymic
surveys [6] did not give such results.
One can notice that the significant long distance divergence was
observed only in those species with good sample size. It is probable that if
all species analyzed here had been represented by larger samples, more
than two cases of differentiation would be described. On the other hand,
Champsocephalus gunnari was not structured with sufficiently large
samples in the three populations analyzed [6]. It is possible that Antarctic
species are more structured due to local isolation than subAntarctic
species as observed from chromosomal data (unpublished).
Structure of Chionodraco myersi populations in the Weddell Sea
Among the four populations considered, three are located in Weddell Sea.
Among them, two (no. 6 and 8) are precisely located near Norvegia Cape,
and the other in Halley Bay. The population 7 remains different from the
two others. The physicochemical characteristics of that station [16] cannot
explain the structure. Nevertheless, the Norvegia Cape, at the level of the
slope break in the continental sh~lf, presents a rapid geotrophic stream
running to the South (20 cm sec ). That peculiarity could provoke the
isolation from the population 7. Thus there could not be any larval
mixture due to the pelagic fry often permitting gene flow.