VII. DESERT FISHES
461
ecology of these critical life-history stages scarcely exists, except as scattered bits in works dealing with other aspects of biology of various species.
We have included such data in other sections, where appropriate, and include this brief statement to emphasize the need for research. Other than
for salmonids, pelagic marine clupeoids, and a few other groups mostly
of commercial importance, this field remains essentially untapped.
3. Environmental Influences on Morphology
Influence of environment on morphology of fishes has long been of interest to ichthyologists. Jordan (1891) established the general principle that
numbers of vertebrae, and therefore body segments, increase as average
temperature decreases. This principle has been further examined and expanded to include other meristic features and body proportions relative
to temperature and other environmental factors (Hubbs, 1922, Tâning,
1952; Itazawa, 1959; Barlow, 1961c; Sweet and Kinne, 1964). Variability
of some desert fish habitats markedly contrasts with constancy of others.
Superimposed on this is the isolation in some, versus lack of isolation
in other, habitats. These factors, of major importance in the biology of
desert fishes, are especially well illustrated in a consideration of the influence of environment on morphology.
Miller (1948) found no consistent correlation between environmental
temperatures and meristics among several subspecies of Cyprinodon nevadensis. In general, populations living in warmer waters collectively averaged lower numbers of meristic features than those living in cooler waters.
These populations were, however, isolated from each other, and considerable variation occurred from spring to spring. Comparisons within the various isolated stocks indicated headspring fish of each subspecies examined
had lower numbers of segmental features than did fish from the outflows
(which averaged cooler). The various populations of pupfishes also maintained considerable stability in meristic phenotype through time, regardless
of whether they lived under constant or variable habitat conditions.
Morphology of each pupfish population presumably responded to environmental influences within the limits of genetic plasticity of the stock,
and local environment comprised a complex of factors to which the genetic
materials available responded in an average manner. Similar data have
been compiled for various populations of Cyprinodon bifasciatus in the
Cuatro Ciénegas basin (Minckley et al, 1971). It is notable here that remarkable stability in morphology has also been detected in stream-fish
populations that have been subjected to marked environmental change in
the past few years (Rinne, 1969), and even in subpopulations of a hybrid
swarm of pupfishes (Minckley, 1969b, and unpublished data).
A lack of expected correlation between meristics and temperature in
461
ecology of these critical life-history stages scarcely exists, except as scattered bits in works dealing with other aspects of biology of various species.
We have included such data in other sections, where appropriate, and include this brief statement to emphasize the need for research. Other than
for salmonids, pelagic marine clupeoids, and a few other groups mostly
of commercial importance, this field remains essentially untapped.
3. Environmental Influences on Morphology
Influence of environment on morphology of fishes has long been of interest to ichthyologists. Jordan (1891) established the general principle that
numbers of vertebrae, and therefore body segments, increase as average
temperature decreases. This principle has been further examined and expanded to include other meristic features and body proportions relative
to temperature and other environmental factors (Hubbs, 1922, Tâning,
1952; Itazawa, 1959; Barlow, 1961c; Sweet and Kinne, 1964). Variability
of some desert fish habitats markedly contrasts with constancy of others.
Superimposed on this is the isolation in some, versus lack of isolation
in other, habitats. These factors, of major importance in the biology of
desert fishes, are especially well illustrated in a consideration of the influence of environment on morphology.
Miller (1948) found no consistent correlation between environmental
temperatures and meristics among several subspecies of Cyprinodon nevadensis. In general, populations living in warmer waters collectively averaged lower numbers of meristic features than those living in cooler waters.
These populations were, however, isolated from each other, and considerable variation occurred from spring to spring. Comparisons within the various isolated stocks indicated headspring fish of each subspecies examined
had lower numbers of segmental features than did fish from the outflows
(which averaged cooler). The various populations of pupfishes also maintained considerable stability in meristic phenotype through time, regardless
of whether they lived under constant or variable habitat conditions.
Morphology of each pupfish population presumably responded to environmental influences within the limits of genetic plasticity of the stock,
and local environment comprised a complex of factors to which the genetic
materials available responded in an average manner. Similar data have
been compiled for various populations of Cyprinodon bifasciatus in the
Cuatro Ciénegas basin (Minckley et al, 1971). It is notable here that remarkable stability in morphology has also been detected in stream-fish
populations that have been subjected to marked environmental change in
the past few years (Rinne, 1969), and even in subpopulations of a hybrid
swarm of pupfishes (Minckley, 1969b, and unpublished data).
A lack of expected correlation between meristics and temperature in