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Geographic variation in energy storage and physiological responses to freezing in the gray treefrogs Hyla versicolor and H. chrysoscelis

Jason T. Irwin^1,* and Jr Richard E. Lee²

¹ Department of Biology, Bucknell University, Lewisburg, PA USA 17837, USA
² Department of Zoology, Miami University, Oxford, OH USA 45056, USA

View larger version (15K): [in a new window]   Fig. 1. Differences in standard body mass among the populations and species (both control and frozen frogs are included in each mean). Means not sharing a letter were significantly different (Bonferroni multiple comparison, =0.05). IN, Indiana; MN, Minnesota; MO, Missouri; Hc, H. chrysoscelis; Hv, H. versicolor.

View larger version (38K): [in a new window]   Fig. 2. Glucose (A,B), glycerol (C,D), and lactate (E,F) concentrations in the liver (A,C,E) and thigh muscle (B,D,F) of control (black bars) and frozen (white bars) frogs. Freezing significantly increased tissue glucose concentration (liver: F=719, P<0.001; thigh muscle: F=81.1, P<0.001) and lactate concentration (liver: F=17.9, P>0.001; thigh muscle: F=19.8, P<0.001). When letters are present, means not sharing a letter were significantly different. Abbreviations as in Fig. 1.

View larger version (21K): [in a new window]   Fig. 3. Liver (A) and thigh muscle (B) tissue water content of control (black bars) and frozen (white bars) frogs. Liver water content always fell significantly with freezing, but there were no differences between species or among the populations within the control or frozen groups. Abbreviations as in Fig. 1.

View larger version (17K): [in a new window]   Fig. 4. Liver (A) and thigh muscle (B) glycogen concentration (in glucose units) for control frogs of the various species and populations sampled. There were no significant differences among the control frogs in liver concentration but MN frogs had higher muscle concentration. Abbreviations as in Fig. 1.

View larger version (13K): [in a new window]   Fig. 5. (A) Total liver glycogen in control frogs estimated by multiplying liver glycogen concentration (µmol g–1 dry mass) by intact liver mass. (B) Total carcass lipid content. (C) Ratio of liver glycogen to carcass lipid content. In all cases means not sharing a letter were significantly different (Bonferroni multiple comparison, =0.05). IN, Indiana; MN, Minnesota; MO, Missouri.

View larger version (13K): [in a new window]   Fig. 6. The ice content of frogs from several populations/species after freezing to -2.5°C. Minnesota frogs accumulated more ice than the Indiana frogs. IN, Indiana; MN, Minnesota; MO, Missouri; Hc, H. chrysoscelis; Hv, H. versicolor.