Adaptive variability of blood-forming elements in the annual life cycle of ground squirrels Urocitellus undulatus

In this study, changes in all blood formed elements of long-tailed ground squirrel Urocitellus undulatus (n=100) during different periods of their life activity were investigated. The hematological analysis was performed on an automatic veterinary analyser: a indices of leukocytes, platelets and erythrocytes were measured in summer (normothermia, june-july), autumn (preparatory period, october), winter torpid (hypothermia, december-february) and winter active periods (IBA, euthermia, short awakenings between hypothermia stages, december-february). It was shown that the total counts of platelets and leukocytes of ground squirrel increased by ~40 % in autumn compared to summer. During the torpor period, thrombocytosis and leukocytosis were replaced by extreme thrombocytopenia (~90 %) and leukopenia (~80 %). On awakening, the indices reached “summer” values, except for a slightly increased mean platelets volume. In autumn, an insignificant erythrocytosis (~10 %) was observed, which, together with changes in other parameters, could indicate an unexpressed autumn hypoxia. In torpor and in winter euthermia, the erythrocyte indices were no difference with summer control values; however, the presence of atypical forms of erythrocytes was detected both in the autumn period of preparation for hibernation and during hibernation. The results are discussed in the context of the adaptation of the blood-forming elements of the ground squirrel to the extreme conditions of hibernation and are valuable for the study of the adaptive abilities of homoeothermic animals and humans.