Four Years in Notothenioid Systematics: A Molecular Perspective
267
[9,16] with high bootstrap proportions. In each of these data sets, no
mutational saturation was detectable among members of the ingroup, and
no significant deviation of base composition shared by some taxa and the
outgroup could be suspected to provoke a false grouping of these taxa
closer to the outgroups. Last but not least, retention indices were rather
good (0.73 in [16]; 0.704 within the ingroup for Lecointre et al. [10]),
showing that homoplasy was not predominant in these diverse data.
The mitochondrial and nuclear sequence data for notothenioids therefore
reliably demonstrate the paraphyly of bovichtids and the paraphyly of
nototheniids. These basal paraphylies are not artefactual and one can
notice that, in the mtDNA tree, a symmetric topology appears relatively
early in the topology because of the numerous members of the genus
Trematomus clustered with Pagothenia. Once these paraphylies are
technically demonstrated, the epistemological causes can be raised. Most
authors will readily admit that bovichtids and nototheniids are
paraphyletic: these families were morphologically very poorly defined or
were defined on the basis of symplesiomorphies (i.e. shared primitive
characters [1,8,10]). This feature is very common in the history of
systematics. Whatever the characters phylogenies are based on, a cladistic
procedure will more often demonstrate the paraphyly of a group
previously considered as monophyletic (in the sense of Mayr [24]) or
merely justified as useful (prokaryotes, bryophytes, pterydophytes,
invertebrates, agnathans, fishes, reptiles, pro simians, etc.) rather than
establishing the monophyly of previously unclassified or dispersed
lineages (Otocephala, Archonta). This is only due to the fact that, between
Darwin and Hennig, we have spent a century to define groups on
diagnoses made of a mixture of shared primitive characters (characters too
general for the scope of the study, i.e. already present in outgroups) and
shared derived characters or, more trivially, diagnoses based on global
similarity from which finalism and anthropocentrism were not excluded
[25]. Defining a group on the basis of shared primitive characters is surely
making a grade, i.e. a paraphyletic unit [26]. A technical consequence of
this is that, since a method, cladistics, proposes that the only way to create
strictly monophyletic groups (holophyletic groups of Mayr) is to define
them exclusively on the basis of common derived characters (i.e.
synapomorphies), the destiny of a huge number of taxa is to explode into a
Hennig's comb. It was the case, for instance in actinopterygian phylogeny,
for paleoniscides, holosteans, protacanthopterygians, malacopterygians,
etc. This is also true at lower taxonomic levels and also true when
revealed by molecular studies: only two out of six notothenioid families
remained monophyletic; and only one out of seven to eight cyprinid
subfamilies remained monophyletic [27].
267
[9,16] with high bootstrap proportions. In each of these data sets, no
mutational saturation was detectable among members of the ingroup, and
no significant deviation of base composition shared by some taxa and the
outgroup could be suspected to provoke a false grouping of these taxa
closer to the outgroups. Last but not least, retention indices were rather
good (0.73 in [16]; 0.704 within the ingroup for Lecointre et al. [10]),
showing that homoplasy was not predominant in these diverse data.
The mitochondrial and nuclear sequence data for notothenioids therefore
reliably demonstrate the paraphyly of bovichtids and the paraphyly of
nototheniids. These basal paraphylies are not artefactual and one can
notice that, in the mtDNA tree, a symmetric topology appears relatively
early in the topology because of the numerous members of the genus
Trematomus clustered with Pagothenia. Once these paraphylies are
technically demonstrated, the epistemological causes can be raised. Most
authors will readily admit that bovichtids and nototheniids are
paraphyletic: these families were morphologically very poorly defined or
were defined on the basis of symplesiomorphies (i.e. shared primitive
characters [1,8,10]). This feature is very common in the history of
systematics. Whatever the characters phylogenies are based on, a cladistic
procedure will more often demonstrate the paraphyly of a group
previously considered as monophyletic (in the sense of Mayr [24]) or
merely justified as useful (prokaryotes, bryophytes, pterydophytes,
invertebrates, agnathans, fishes, reptiles, pro simians, etc.) rather than
establishing the monophyly of previously unclassified or dispersed
lineages (Otocephala, Archonta). This is only due to the fact that, between
Darwin and Hennig, we have spent a century to define groups on
diagnoses made of a mixture of shared primitive characters (characters too
general for the scope of the study, i.e. already present in outgroups) and
shared derived characters or, more trivially, diagnoses based on global
similarity from which finalism and anthropocentrism were not excluded
[25]. Defining a group on the basis of shared primitive characters is surely
making a grade, i.e. a paraphyletic unit [26]. A technical consequence of
this is that, since a method, cladistics, proposes that the only way to create
strictly monophyletic groups (holophyletic groups of Mayr) is to define
them exclusively on the basis of common derived characters (i.e.
synapomorphies), the destiny of a huge number of taxa is to explode into a
Hennig's comb. It was the case, for instance in actinopterygian phylogeny,
for paleoniscides, holosteans, protacanthopterygians, malacopterygians,
etc. This is also true at lower taxonomic levels and also true when
revealed by molecular studies: only two out of six notothenioid families
remained monophyletic; and only one out of seven to eight cyprinid
subfamilies remained monophyletic [27].