LATITUDINAL EFFECTS ON METABOLIC RATES IN THE CRICKET FROG, ACRIS CREPITANS: ACUTELY MEASURED RATES IN SUMMER FROGS

¹ Department of Biology, University of South Dakota, Vermillion, South Dakota

Samples of cricket frogs were collected in Texas and in South Dakota in July and acclimated for 5-7days at 15 and 25° C. Routine metabolic rates were determined at 5, 10, 15, 20, 25, 30, and 35° C for samples from both localities acclimated at both temperatures. Sets of data from samples determined at each of the seven determination temperatures were subjected to a 2 x 2 analysis of covariance.

For both localities, warm acclimated (25° C) frogs had higher metabolic rates than cool acclimated (15° C) frogs at determination temperatures below 20° C (Texas) or below 25° C (South Dakota). At determination temperatures from 25 to 35° C (South Dakota) and 20 to 30° C (Texas), acclimation effects were not significant. At 35° C, Texas frogs acclimated at 15° C had a higher metabolic rate than those acclimated at 25° C.

Frogs acclimated at 15° C showed no significant locality effects when determined at 5, 10, 15, 25, and 35° C. At 20° C, the Texas frogs acclimated at 15° C had a significantly higher rate than the corresponding South Dakota frogs, while at 30° C, the South Dakota frogs had the higher rate. When both were acclimated at 25° C, the South Dakota frogs had a significantly higher rate than those from Texas at determination temperatures of 10, 15, 30, and 35° C. At 5, 20, and 25° C, however, no significant locality effects were apparent.

On the acutely measured R-T curves of cricket frogs acclimated at 25° C, there is a region of pronounced metabolic insensitivity to temperature in which region the Q₁₀ approximates 1.0. The region lies between determination temperatures of 15-25° C for the South Dakota frogs and between 20-30° C for the Texas animals. Frogs from both localities acclimated at 15° C have a low Q₁₀ value between 10-15° C and the Texas frogs have another one between 20 and 30° C. The differences noted above between the warm acclimated R-T curves of the northern and southern populations, taken in conjunction with published data on body temperature-environmental temperature relationships in Acris and with published climatological data, are consistent with the hypothesis of the role of metabolic patterns in the maintenance of metabolic stability in a varying thermal environment.