Physiological indices of the even-toothed shrew (Sorex isodon, Eulipotyphla) during short-term exposure to cold water
Authors:   Institute of the Biological Problems of the North, Far-East Branch of the Russian Academy of Science, Kiselev Sergey V. 
Published: October 2024

The physiological indices of small mammals caught in the natural environment are used to assess their living conditions, analyze the impact of various factors on populations, identify the mechanisms of animal adaptation to these factors, and for other purposes. At the same time, pitfall traps with water are often used to capture animals, especially shrews. The water temperature in such traps is characterized by rather low values. Even a relatively short stay of animals in cold water can lead to changes in their physiological parameters, which must be taken into account. The aim of this study was to evaluate such changes in shrews, on example of Sorex isodon. The variability of the physiological parameters of shrews during immersion in cold water is also of interest from the point of view of their physiology of thermoregulation. Shrews are among the smallest mammals, and therefore are characterized by high rates of heat loss. At the same time, these animals are active all year round and are widely distributed in the northern regions, where they are often exposed to acute cold exposure. The physiological mechanisms of adaptation of shrews to such conditions are still insufficiently studied. The study was conducted in late July-August 2016 on immature young-of-the-year even-toothed shrews (Sorex isodon Turov, 1924). The capture of shrews was carried out in the vicinity of Magadan (Russia). Before the start of the experiment, the caught animals had been kept individually for 2 days in plastic containers (37x26x26 cm) at room temperature with the provision of water and food ad libitum. Control animals were decapitated under ether anesthesia after keeping. The experimental animals were placed in a container with water preliminarily cooled to 4.5-9°C (6.5°C on average). After the swimming intensity of the shrews significantly decreased, they were also subjected to anesthesia and decapitation. The experimental group consisted of 22, and the control group consisted of 21 animals. The following physiological indices were determined in the shrews: blood glucose level, glycogen and lipid content in the liver, mass of internal organs and fat reserves, and the number of bone marrow cells in the femur. For statistical analyses, the Mann-Whitney U-test was used. The average swimming time of S. isodon in the experiment was 5.8 minutes. A relatively short immersion in cold water led to a significant change in the values of some physiological parameters in S. isodon. The indices of energy metabolism showed greatest differences between the control and experimental groups of animals. The level of blood glucose in S. isodon in the test group was significantly higher (See Fig. 1). On the contrary, the liver glycogen content in shrews sharply decreased after the experimental treatment. The level of this carbohydrate in the experimental group was 80% less than in the control. Acute cold exposure also provoked a fairly rapid change in the mass of fat reserves in S. isodon. The absolute and relative mass of the interscapular adipose tissue of S. isodon decreased by 11.9% and 10.7%, respectively, and that of the inguinal adipose tissue, by 20.9% and 18.8%, respectively (See Table 1). Differences in the mass of some shrew organs were also significant. The absolute and relative weight of the spleen was higher in the experimental animals. After exposure to cold water, S. isodon also had a higher relative heart mass than controls, although the differences in the absolute mass of this organ were insignificant. On the contrary, the absolute mass of shrew kidneys decreased after immersion in cold water. All other physiological indices showed no significant differences between the groups of control and experimental S. isodon. Thus, a relatively short stay of shrews in cold water provokes a significant change in the mass of their adipose tissue and some organs. High demand for glucose during acute cold stress leads to rapid depletion of liver glycogen. The rate of reduction of fat reserves in shrews under cold exposure is also quite high and exceeds that of most other mammals. It is known that in regions characterized by severe climatic conditions, the rate of reserve fat mobilization is of great importance for the survival of small mammals. The ability to quickly store and spend fat reserves, therefore, seems to be an important adaptation of shrews to living in cold climates.