260
L. Bargelloni and G. Lecointre
hemoglobins [4]. Among morphological modifications, certainly
remarkable is the evolution of neutral buoyancy, in the absence of a swim
bladder, as shown by some notothenioid species, which can be likely
considered an adaptation to the pelagic niche [5].
All these peculiar features as well as their ecological success make the
study of notothenioid evolution extremely interesting.
In recent years, the necessity of using phylogenetic trees in comparing
physiological, behavioral and ecological traits among different taxa has
become evident [6]. Hence, a solid knowledge ofnotothenioid systematics
is important not only for taxonomic purposes but also as an essential tool
for any evolutionary study on this group of organisms.
Until recently, reconstruction of notothenioid relationships has been
based on morphological characters, with "conservative" results. Iwami in
1985 [7] and Hastings in 1993 [8] produced notothenioid cladograms
where each notothenioid family appeared as monophyletic (except
bathydraconids which were paraphyletic in Hasting'S cladogram).
Since 1993 our two groups have undertaken a long-term project aimed
at reconstructing the phylogenetic relationships among and within
notothenioid families based on DNA sequence data. These studies have
been focused on two mitochondrial genes, respectively encoding for the
large (16S) and the small (12S) subunit of ribosomal RNA [9], as well as
on the nuclear gene for the 28S subunit of ribosomal RNA [10]. Sequence
information from these ribosomal genes, in fact, has proved to be very
useful in the reconstruction of the phylogenetic relationships in various
taxonomic groups.
In the present paper we summarize previous data on notothenioid
systematics, in the light of new results stemming from the analysis of a
larger number of taxa.
Phylogenetic Methods
Using a methodological approach already described [9], 33 notothenioid
species were examined as listed in Table 1. The zoarcids Lycodichthys
dearborni and Pachycara brachycephalum were included in the study as
outgroup. Phylogenetic analyses were performed by maximum parsimony
(MP), using the PAUP 3.1.1 computer program [11].
The reliability of the heuristic searches was improved by using the
option "random addition of taxa" with 100 replications in PAUP. Several
different character weighting schemes were used [9].
Statistical confidence ofMP trees was assessed using bootstrapping [12]
with 200 replications each. The obtained topology was also compared to
L. Bargelloni and G. Lecointre
hemoglobins [4]. Among morphological modifications, certainly
remarkable is the evolution of neutral buoyancy, in the absence of a swim
bladder, as shown by some notothenioid species, which can be likely
considered an adaptation to the pelagic niche [5].
All these peculiar features as well as their ecological success make the
study of notothenioid evolution extremely interesting.
In recent years, the necessity of using phylogenetic trees in comparing
physiological, behavioral and ecological traits among different taxa has
become evident [6]. Hence, a solid knowledge ofnotothenioid systematics
is important not only for taxonomic purposes but also as an essential tool
for any evolutionary study on this group of organisms.
Until recently, reconstruction of notothenioid relationships has been
based on morphological characters, with "conservative" results. Iwami in
1985 [7] and Hastings in 1993 [8] produced notothenioid cladograms
where each notothenioid family appeared as monophyletic (except
bathydraconids which were paraphyletic in Hasting'S cladogram).
Since 1993 our two groups have undertaken a long-term project aimed
at reconstructing the phylogenetic relationships among and within
notothenioid families based on DNA sequence data. These studies have
been focused on two mitochondrial genes, respectively encoding for the
large (16S) and the small (12S) subunit of ribosomal RNA [9], as well as
on the nuclear gene for the 28S subunit of ribosomal RNA [10]. Sequence
information from these ribosomal genes, in fact, has proved to be very
useful in the reconstruction of the phylogenetic relationships in various
taxonomic groups.
In the present paper we summarize previous data on notothenioid
systematics, in the light of new results stemming from the analysis of a
larger number of taxa.
Phylogenetic Methods
Using a methodological approach already described [9], 33 notothenioid
species were examined as listed in Table 1. The zoarcids Lycodichthys
dearborni and Pachycara brachycephalum were included in the study as
outgroup. Phylogenetic analyses were performed by maximum parsimony
(MP), using the PAUP 3.1.1 computer program [11].
The reliability of the heuristic searches was improved by using the
option "random addition of taxa" with 100 replications in PAUP. Several
different character weighting schemes were used [9].
Statistical confidence ofMP trees was assessed using bootstrapping [12]
with 200 replications each. The obtained topology was also compared to