Temperature and Development of the Wood Frog, Rana Sylvatica, in Alaska

Wood frogs breed in a variety of ponds and lakes in central Alaska. Dates of first appearance of frogs ranged from 24 April to 22 May. Egg laying began 4—6 days later. Egg laying was completed in a pond 4—8 days after the first egg mass appeared. Wood frogs tend to lay their egg masses at the same spot. The average number of eggs per mass was 778 with an egg diameter of 1.6 mm. Development of eggs was directly related to water temperature and occured at the same rate as that shown for wood frogs from New York. Temperature limits that permit at least 50% survival of eggs through hatching were 6°—24°C. Temperature tolerance of eggs and tadpoles varied with age and acclimatization. Temperature preference of tadpoles followed a normal curve and ranged from 9° to 29°C. Development in the field varied among different ponds and different years. Rapid growth occured once the larvae were free swimming. Average maximum weight ranged from 2.15 to 2.85 g; maximum length varied from 5.5 to 6.0 cm. Time to metamorephosis ranged from 53 to 78 days. Two periods of development are distinguished: In period I, fertilization to free—living stage, growth rate is determined by water temperature. This period occupies one—third of the development time but has a higher mortality rate than period II. The later period includes the free—swimming stage until climax metamorphosis, and development rate is determined by environmental factors such as food and population density, as well as temperature.