Graduate Thesis Or Dissertation
 

The ecology of Lepidurus apus in northern Utah and some limnological requirements for hatching

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  • 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.
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