Abstract
A total of 242 Cnemidophorus sexlineatus were collected in biweekly samples from east-central Alabama and west-central Georgia during the period May 1978 to September 1979. Blood, collected in the field, was returned to the lab and subjected to a radioimmunoassay for thyroxine (T 4). Mean biweekly plasma T 4 titers (ranging from 1.0 to 4.2 ng/ml) were plotted against the collection date. Analysis of these data indicated the presence of a significant ( P < 0.01) quadratic (curvilinear) response with lower titers during the summer months of activity and higher titers during other months, thus suggesting definite seasonal changes in plasma T 4 titers. These seasonal fluctuations could not be definitively explained in terms of changes in temperature, reproductive condition, or fat stores. Rather, these abrupt seasonal changes in plasma T 4 titers coincided best with the entry into and emergence from hibernation. Plasma T 4 titers of hibernating lizards were found to be significantly higher ( P < 0.05) than those of active lizards.
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