Induction of summer hibernation in the 13-lined ground squirrel shown by comparative serum transfusions from arctic mammals.

A “trigger” substance was again indicated to be present in sera of hibernating animals. Sera from the hibernating 13-lined ground squirrel, hibernating woodchuck, hibernating Arctic ground squirrel, and hibernating Arctic marmot were all capable of inducing the 13-lined ground squirrel to hibernate in the summer, a season when that species would normally be active. The hibernation trigger is thus not species specific. It is effective whether drawn from these two Arctic species of hibernators or drawn from these two species of hibernators from the midwestern states. The normothermic Arctic marmot appears to have an “anti-trigger” substance in its serum in the summer, which impedes fall hibernation in the transfused 13-lined ground squirrel. This is similar to the anti-trigger observed in the summer serum of active 13-lined ground squirrels and active woodchucks. With respect to hypothermia, it was induced in Artic marmots and in Arctic foxes at Point Barrow, Alaska, in summer. Though in such cases body temperatures fell significantly (as in hibernation), no trigger was recovered from their hypothermic sera that could be shown to be capable of inducing summer hibernation in the ground squirrel. Neither was anti-trigger found in the serum of hypothermic experimentals. These latter experiments thus suggest that the release of trigger into the blood during hibernation is dependent on a mechanism more complex than simply lowering body temperature.