462
JAMES E. DEACON AND W. L. MINCKLEY
isolated populations of desert fishes may result from independent differentiation of the stocks. The general reality of such correlation in fishes of
more continuous distribution, i.e., in freshwaters of more mesic zones or
in the sea, suggests the requisite of gene flow if such a pattern is to be
maintained. More broadly stated, genetic continuity permits expression of
environmental influences while isolation may obscure such effects.
Notwithstanding such complications, there appears a direct tendency
for greater numbers of scales in western American pupfishes inhabiting
more saline waters. In most instances there seems an inverse relationship
between number of fin rays and salinity (Miller, 1948, 1950b; LaBounty,
1968; LaBounty and Deacon, 1971). A direct relationship between
salinity and number of rays on the second dorsal fin and anal fin
was recently demonstrated for two populations of an Australian atherinid
(Taeniomembras sp.) (Lee and Williams, 1970). Other features appear
in warm-spring fishes, viz., the dorsal fin seems to be farther back on the
body; the head, eye, and anterior part of the body is greater in size (perhaps relating in part to greater gill area (Section III,B,3); the fins are
often more expansive and the body sizes tend to be smaller (Hubbs and
Kuehne, 1937; Miller, 1948, 1950b). In many respects these features indicate neoteny, and the last characteristics to appear during ontogeny are
most labile (Barlow, 1961c).
Sweet and Kinne (1964) have done some of the most thorough studies
presently available on fish body shape as influenced by temperature, salinity, and a combination of those factors. At 35 gm/liter salinity, the level
at which all eggs were laid, relative body shape of desert pupfish at hatching remained isometric under all experimental incubation temperatures.
However, eggs transferred either to higher or lower salinities after deposition showed thermal responses in body shape. Body depth and width at
hatching were greater at lower salinities (which produced a rounder fish
with a smaller surface area to volume ratio), and all body dimensions were
smaller when development proceeded at higher salinities. Body lengths at
hatching in fresh water were greatest at 32°-33°C, and decreased when development was at either higher or lower temperatures. In water of
35 gm/liter salinity, body length was less at hatching at each successively
higher temperature (tests were not made at lower than 28°C). Blaxter
(1969) suggested that the preceding data probably reflect existence of temperature (and salinity?) optima for yolk utilization by the embryos. It
should be noted that while length at hatching of desert pupfish at 31.8°C
was maximal in fresh water, and decreased with increasing salinities
(Kinne and Kinne, 1962a), final sizes in the salinity ranges from fresh
to 35 gm/liter were not significantly different, at least at the moderate temperature of about 25°C (Kinne, 1965).
JAMES E. DEACON AND W. L. MINCKLEY
isolated populations of desert fishes may result from independent differentiation of the stocks. The general reality of such correlation in fishes of
more continuous distribution, i.e., in freshwaters of more mesic zones or
in the sea, suggests the requisite of gene flow if such a pattern is to be
maintained. More broadly stated, genetic continuity permits expression of
environmental influences while isolation may obscure such effects.
Notwithstanding such complications, there appears a direct tendency
for greater numbers of scales in western American pupfishes inhabiting
more saline waters. In most instances there seems an inverse relationship
between number of fin rays and salinity (Miller, 1948, 1950b; LaBounty,
1968; LaBounty and Deacon, 1971). A direct relationship between
salinity and number of rays on the second dorsal fin and anal fin
was recently demonstrated for two populations of an Australian atherinid
(Taeniomembras sp.) (Lee and Williams, 1970). Other features appear
in warm-spring fishes, viz., the dorsal fin seems to be farther back on the
body; the head, eye, and anterior part of the body is greater in size (perhaps relating in part to greater gill area (Section III,B,3); the fins are
often more expansive and the body sizes tend to be smaller (Hubbs and
Kuehne, 1937; Miller, 1948, 1950b). In many respects these features indicate neoteny, and the last characteristics to appear during ontogeny are
most labile (Barlow, 1961c).
Sweet and Kinne (1964) have done some of the most thorough studies
presently available on fish body shape as influenced by temperature, salinity, and a combination of those factors. At 35 gm/liter salinity, the level
at which all eggs were laid, relative body shape of desert pupfish at hatching remained isometric under all experimental incubation temperatures.
However, eggs transferred either to higher or lower salinities after deposition showed thermal responses in body shape. Body depth and width at
hatching were greater at lower salinities (which produced a rounder fish
with a smaller surface area to volume ratio), and all body dimensions were
smaller when development proceeded at higher salinities. Body lengths at
hatching in fresh water were greatest at 32°-33°C, and decreased when development was at either higher or lower temperatures. In water of
35 gm/liter salinity, body length was less at hatching at each successively
higher temperature (tests were not made at lower than 28°C). Blaxter
(1969) suggested that the preceding data probably reflect existence of temperature (and salinity?) optima for yolk utilization by the embryos. It
should be noted that while length at hatching of desert pupfish at 31.8°C
was maximal in fresh water, and decreased with increasing salinities
(Kinne and Kinne, 1962a), final sizes in the salinity ranges from fresh
to 35 gm/liter were not significantly different, at least at the moderate temperature of about 25°C (Kinne, 1965).