8
J.T. Eastman and A. Clarke
diversity [31]. The family includes about 200 species living from the
intertidal zone to depths of 7000 m [4,21,32]. Liparids probably originated
and radiated in the North Pacific Region with subsequent dispersal
southward along the western coast of the Americas [33,34]. In the deep
waters of the Antarctic Region liparids underwent a secondary radiation
complementing the shallow water radiation of perciform notothenioids. All
known species are members of deep-water genera [35]; most are epibenthic
at depths of 200-2000 m [4]. As the sea below 200 m is the largest living
space on earth, it is reasonable to expect that it would be subject, with
some constraints, to the same evolutionary processes occurring in other
aquatic environments.
Although phyletically diverse, many Antarctic liparids are known from
only a few specimens. They are taxonomically dominant in waters over
500-600 m deep, but may not be represented by large populations and
biomass [4]. Liparids lack a swim bladder and phyletic ally primitive
species are inshore benthic fish [36], but the liparid radiation in the
Antarctic Region has centered on diversification into the water column,
especially epibenthic niches. The amount of morphological divergence
relative to lineage splitting reflects the degree of macroevolution and, if
families are compared, this has been considerably less in liparids than in
nototheniids.
Since they are few in number, deep-living and difficult to maintain in
aquaria, we know little of the biology of Antarctic liparids. The sole
exception is Paraliparis devriesi which lives at 500-650 m in McMurdo
Sound. Although lacking a swim bladder, this species is neutrally buoyant
through the combined effects of reduced skeletal ossification and
expansion of a watery gelatinous subdermal extracellular matrix consisting
of glycosaminoglycans. This matrix serves as a low density buoyancy
agent comprising about one-third of the body weight, the largest known
proportion of any adult fish [37]. At nearly 78°S the population of P.
devriesi in McMurdo Sound has the most southerly distribution of any
known liparid, living in water with a temperature of about -1.9 °C and little
seasonal variation. However only small amounts of antifreeze compounds
have been inferred from the melting point-freezing point behavior of body
fluids. Freezing avoidance in P. devriesi may therefore be the result of the
combined effects of modest concentrations of a noncolligative antifreeze
and elevated osmolality of body fluids [38].
The Environmental Background to the Evolution of the
Antarctic Continental Shelf Fauna
The evolution of the Antarctic fish fauna can only be understood in relation
J.T. Eastman and A. Clarke
diversity [31]. The family includes about 200 species living from the
intertidal zone to depths of 7000 m [4,21,32]. Liparids probably originated
and radiated in the North Pacific Region with subsequent dispersal
southward along the western coast of the Americas [33,34]. In the deep
waters of the Antarctic Region liparids underwent a secondary radiation
complementing the shallow water radiation of perciform notothenioids. All
known species are members of deep-water genera [35]; most are epibenthic
at depths of 200-2000 m [4]. As the sea below 200 m is the largest living
space on earth, it is reasonable to expect that it would be subject, with
some constraints, to the same evolutionary processes occurring in other
aquatic environments.
Although phyletically diverse, many Antarctic liparids are known from
only a few specimens. They are taxonomically dominant in waters over
500-600 m deep, but may not be represented by large populations and
biomass [4]. Liparids lack a swim bladder and phyletic ally primitive
species are inshore benthic fish [36], but the liparid radiation in the
Antarctic Region has centered on diversification into the water column,
especially epibenthic niches. The amount of morphological divergence
relative to lineage splitting reflects the degree of macroevolution and, if
families are compared, this has been considerably less in liparids than in
nototheniids.
Since they are few in number, deep-living and difficult to maintain in
aquaria, we know little of the biology of Antarctic liparids. The sole
exception is Paraliparis devriesi which lives at 500-650 m in McMurdo
Sound. Although lacking a swim bladder, this species is neutrally buoyant
through the combined effects of reduced skeletal ossification and
expansion of a watery gelatinous subdermal extracellular matrix consisting
of glycosaminoglycans. This matrix serves as a low density buoyancy
agent comprising about one-third of the body weight, the largest known
proportion of any adult fish [37]. At nearly 78°S the population of P.
devriesi in McMurdo Sound has the most southerly distribution of any
known liparid, living in water with a temperature of about -1.9 °C and little
seasonal variation. However only small amounts of antifreeze compounds
have been inferred from the melting point-freezing point behavior of body
fluids. Freezing avoidance in P. devriesi may therefore be the result of the
combined effects of modest concentrations of a noncolligative antifreeze
and elevated osmolality of body fluids [38].
The Environmental Background to the Evolution of the
Antarctic Continental Shelf Fauna
The evolution of the Antarctic fish fauna can only be understood in relation