Phylogeny of the Channichthyidae (Notothenioidei, Teleostei)
293
Secondly, looking at the distances used and her conclusions, Cryodraco
is actually the most extreme taxon, i.e. it has the slowest rate of
osteological development, as concluded in her abstract. However, the fact
that the rerooted tree of Voskoboinikova is the same as ours is an
interesting point.
This shows that the slowdown of the rate of the osteological development
regularly follows the successive cladogeneses within the family without
detectable homoplastic alterations of this rate. In other words, the most
derived channichthyids are the most pedomorphic.
Cladogenetic Features
The examination of lifestyle, bathymetric distribution and geographic
distribution of each species and mapping these three parameters on our tree
(Fig. 1) provide an interesting outcome. We have first to remember some
methodological aspects. A cladogram is neither an evolutionary story, nor a
scenario. It is just a distribution of characters among taxa. Therefore, a
node is not the direct reflection of a speciation leading to two species. The
dichotomic nature of the node is simply due to the fact that the cladogram
has reached its maximum explanatory power, in other words corresponds
to the maximum resolution in the tree. To a single cladogram correspond
many possible scenarios where nodes are speciation events [18-20]. Most
of the time, a cladogram does not allow us to exhaust all the descriptive
and/or causal elements that can be assumed to describe or explain
speciations. For this reason, mapping the three above features has poor
chance to explain something. However, in the present case, the striking
conclusion of such a mapping is that each c1adogenesis of Fig. 1
corresponds to the differentiation of one of these three parameters (Fig. 4),
what was initially rather unexpected. We would rather expect that at least
some nodes would not differentiate anything at all. Figure 4 shows that
each node (particularly the most terminal ones E, F, H, I, J, G, K, L) can be
correlated to a difference in distribution, depth or lifestyle, in such a way
that each node can be correlated to a hypothetical sympatric speciation
(when the lifestyles of two sister-groups differ, see nodes K, G, Fig. 4) or
hypothetical allopatric speclatIons (when the geographic and/or
bathymetric distributions of two sister-groups differ, see nodes E, F, J, H, I,
J, L, Fig. 4). One must keep in mind that these correlations have no power
to establish causalities; they are just elements for further research. Indeed,
more complex events than described here might have occurred during the
evolution of the family.
293
Secondly, looking at the distances used and her conclusions, Cryodraco
is actually the most extreme taxon, i.e. it has the slowest rate of
osteological development, as concluded in her abstract. However, the fact
that the rerooted tree of Voskoboinikova is the same as ours is an
interesting point.
This shows that the slowdown of the rate of the osteological development
regularly follows the successive cladogeneses within the family without
detectable homoplastic alterations of this rate. In other words, the most
derived channichthyids are the most pedomorphic.
Cladogenetic Features
The examination of lifestyle, bathymetric distribution and geographic
distribution of each species and mapping these three parameters on our tree
(Fig. 1) provide an interesting outcome. We have first to remember some
methodological aspects. A cladogram is neither an evolutionary story, nor a
scenario. It is just a distribution of characters among taxa. Therefore, a
node is not the direct reflection of a speciation leading to two species. The
dichotomic nature of the node is simply due to the fact that the cladogram
has reached its maximum explanatory power, in other words corresponds
to the maximum resolution in the tree. To a single cladogram correspond
many possible scenarios where nodes are speciation events [18-20]. Most
of the time, a cladogram does not allow us to exhaust all the descriptive
and/or causal elements that can be assumed to describe or explain
speciations. For this reason, mapping the three above features has poor
chance to explain something. However, in the present case, the striking
conclusion of such a mapping is that each c1adogenesis of Fig. 1
corresponds to the differentiation of one of these three parameters (Fig. 4),
what was initially rather unexpected. We would rather expect that at least
some nodes would not differentiate anything at all. Figure 4 shows that
each node (particularly the most terminal ones E, F, H, I, J, G, K, L) can be
correlated to a difference in distribution, depth or lifestyle, in such a way
that each node can be correlated to a hypothetical sympatric speciation
(when the lifestyles of two sister-groups differ, see nodes K, G, Fig. 4) or
hypothetical allopatric speclatIons (when the geographic and/or
bathymetric distributions of two sister-groups differ, see nodes E, F, J, H, I,
J, L, Fig. 4). One must keep in mind that these correlations have no power
to establish causalities; they are just elements for further research. Indeed,
more complex events than described here might have occurred during the
evolution of the family.