Abstract:
A survey of the major bodies of water, temporary and perennial,
in the region of Northern Utah revealed a limited distribution of
the Notostraca. Lepidurus (Linn.), the only representative
found, was restricted to a single temporary shallow lake. Dry Lake,
in the southern end of Cache County.
Dry Lake occupies a solution basin at 5,638 feet elevation, surrounded by mountains ranging from 6,500 to 7,900 feet in elevation.
The limnological succession of this lake during the tenure of
L. apus showed a high rate of variation and wide ranges in temperature
(-2°C to 31°C), dissolved oxygen (46% to 155% saturation),
conductivity (1100-3400 mho), turbidity, and pH.
Laboratory incubation of the eggs of L. apus under a total of
120 different combinations of temperature and moisture pre-incubation
treatments, disclosed the necessity of a pre-incubation freezing
treatment to induce hatching. A pre-incubation drying treatment was
not necessary for eggs incubated for 124 days but consistently
produced significantly higher percentages of hatching in those
hatches dried at 18°C and 26°C. Eggs remained viable with but
slight reduction in rate and percentage of hatching, even though
they had undergone -20°C (rapid cooling) and 26°C (drying) pre-incubation
treatments.
Pre-incubation freezing to -80°C, whether rapid or slow,
reduced the percent hatch to a maximum of 12%. The 45°C drying
for 48 hours permitted a maximum of 40% hatching and retarded
significantly the hatching rate.
Sun-dried and wet eggs were subjected to -2°C for periods
varying from 2 days to 37 days. One portion of these dried eggs
was frozen in a dry state and another portion in a wet condition.
Incubation of these eggs in pond water at 5°C, 10°C, 25°C, and
40°C produced hatching solely in the 10°C temperature among those
sun-dried and frozen wet only. A 14 day duration of continuous
cold was found to be a minimal requirement.
Eggs receiving the threshold duration of pre-incubation cold
treatment required 14 days subsequent incubation at 10°C for hatching.
Extension of the pre-incubation cold treatment up to 31 days resulted
in a consequent reduction (not linear, however) of incubation time
at 10°C from 14 to 7 days. Thirty-four and 37 days detention in the
cold (-2°C) showed an increase to 10 days incubation time.
The eggs of L. apus develop and hatch at -2°C, although at
a greatly reduced rate.
