A Comparison of Adaptive Radiations of Antarctic Fish with those of NonAntarctic Fish
7
Notothenioids
The percifonn suborder Notothenioidei includes eight families and 121
species. All but 26 of these species are confined to the Antarctic Region. In
the entire Southern Ocean, about 35% of species are notothenioids; in
subzero shelf and slope waters 46% are notothenioids (Table 1). Here they
occupy virtually all benthic and water column habitats, accounting for 9095% of the biomass [26, 27]. In the eastern and southern Weddell Sea, for
example, 94% of the specimens captured are members of the family
Nototheniidae [28]. This exceptional degree of habitat saturation by a
single taxonomic group is attributable to the fact that notothenioids occupy
niches filled by taxonomically diverse groups of fishes in temperate and
tropical oceans.
A simple count of taxa does not begin to adequately describe the nature
of the notothenioid radiation. In addition to phyletic diversification, and
unlike most other fish groups including some lacustrine radiations [29,30],
notothenioids have also experienced substantial morphological and
ecological diversification in that there are a number of distinct life history
or ecological types. Notothenioids underwent a depth-related
diversification centered on the evolutionary alteration of buoyancy and the
morphology associated with swimming and feeding in the water column.
Although lacking swim bladders, some notothenioids diversified away
from the ancestral benthic habitat toward pelagic or partially pelagic
zooplanktivory and piscivory. Within the family Nototheniidae, for
example, about 50% of the Antarctic species are pelagic, semipelagic,
cryopelagic or epibenthic rather than benthic, the presumed ancestral type
[1]. Referred to as pelagization, this ecomorphological trend toward life in
the water column has arisen independently in at least two different
nototheniid clades, although phylogenetically related species are not
necessarily morphologically and ecologically similar [3].
Liparids
With the recent description of dozens of new species [4], it appears that a
radiation of snailfishes of the scorpaenifonn family Liparidae inhabits the
deep shelf and upper slope of the Antarctic Region. The 64 liparid species
from the Antarctic Region, mostly members of the genera Paraliparis and
Careproctus [4], represent 31 % of the 208 species of benthic fishes from
the continental shelf and upper slope (Table 2). The Liparidae has
surpassed the Nototheniidae as the most speciose fish family in the
Southern Ocean.
Unlike notothenioids, liparids have a worldwide distribution and are one
of the few fish families having both boreal and austral centers of species
7
Notothenioids
The percifonn suborder Notothenioidei includes eight families and 121
species. All but 26 of these species are confined to the Antarctic Region. In
the entire Southern Ocean, about 35% of species are notothenioids; in
subzero shelf and slope waters 46% are notothenioids (Table 1). Here they
occupy virtually all benthic and water column habitats, accounting for 9095% of the biomass [26, 27]. In the eastern and southern Weddell Sea, for
example, 94% of the specimens captured are members of the family
Nototheniidae [28]. This exceptional degree of habitat saturation by a
single taxonomic group is attributable to the fact that notothenioids occupy
niches filled by taxonomically diverse groups of fishes in temperate and
tropical oceans.
A simple count of taxa does not begin to adequately describe the nature
of the notothenioid radiation. In addition to phyletic diversification, and
unlike most other fish groups including some lacustrine radiations [29,30],
notothenioids have also experienced substantial morphological and
ecological diversification in that there are a number of distinct life history
or ecological types. Notothenioids underwent a depth-related
diversification centered on the evolutionary alteration of buoyancy and the
morphology associated with swimming and feeding in the water column.
Although lacking swim bladders, some notothenioids diversified away
from the ancestral benthic habitat toward pelagic or partially pelagic
zooplanktivory and piscivory. Within the family Nototheniidae, for
example, about 50% of the Antarctic species are pelagic, semipelagic,
cryopelagic or epibenthic rather than benthic, the presumed ancestral type
[1]. Referred to as pelagization, this ecomorphological trend toward life in
the water column has arisen independently in at least two different
nototheniid clades, although phylogenetically related species are not
necessarily morphologically and ecologically similar [3].
Liparids
With the recent description of dozens of new species [4], it appears that a
radiation of snailfishes of the scorpaenifonn family Liparidae inhabits the
deep shelf and upper slope of the Antarctic Region. The 64 liparid species
from the Antarctic Region, mostly members of the genera Paraliparis and
Careproctus [4], represent 31 % of the 208 species of benthic fishes from
the continental shelf and upper slope (Table 2). The Liparidae has
surpassed the Nototheniidae as the most speciose fish family in the
Southern Ocean.
Unlike notothenioids, liparids have a worldwide distribution and are one
of the few fish families having both boreal and austral centers of species