Although common shrews in the winter decreases body weight in General and brain in particular, the speed of their metabolism, contrary to environmental regulations, not growing, reported in Royal Society Open Science. The smaller the organism, the faster in terms of per unit mass of the body it is cooled (and the more effort is necessary to maintain a constant temperature), but not for shrews in this pattern is not valid. Interestingly, from oxygen uptake by the brain the metabolic rate of shrews in this case is almost independent.
To maintain a constant body temperature, it is necessary to continuously produce heat, and this requires a lot there. In areas with seasonal climate, availability of food changes periodically, which is equally good to eat at different times of the year difficult or even impossible. Part of the warm-blooded animal solves this problem by reducing the level of activity, falling in a winter sleep or a deeper state of rest — hibernation. Someone makes the reserves in cold or dry periods.
None of these strategies do not adhere to small omnivorous mammals — common shrew (Sorex araneus). They are active in winter and summer, but don’t hoard food. The main seasonal changes in their bodies — reduced mass of individual organs and the whole body for the winter. Common shrews, which live just under two years, born in the summer, grow rapidly and quickly reach their maximum size (length 8 cm, weight 13 grams), and in autumn, their mass drops by about 20 percent. 17 percent decreases the volume of the cranium, and, as a result, shrinks the brain. In the spring of shrew are rising again.
Such paradoxical changes must have adaptive value, but what it is is not known for certain. Researchers from the Institute for the study of animal behavior, max Planck Society, which a few years ago confirmed the seasonal decrease of the brain in S. araneus, suggested that it in reducing oxygen consumption. The brain need more volume of this gas than other organs, so that its compression could save the shrews a lot of energy.
On the other hand, the smaller the volume of the body (assuming it is directly proportional to mass), the lower the surface area of the organism and the faster the animal must be cooled. This pattern is known as the ecological rules of Bergmann. Accordingly, when reducing bodies shrew needs to produce more heat to maintain its normal temperature. For this, they need to speed up the metabolism, although warm-blooded, on the contrary, usually have to slow it down for the winter.
German scientists have verified these theoretical calculations in practice: they caught common shrews in the local woods in January, April and June of 2016 and 2017. Immediately after the capture of zoologists has identified body weight and age of the animals. Then the animals (there were 29) for several days were kept in individual cages with food and water, emergency shelters, and wheels. Periodically, scientists measured the metabolic rate of shrews — the amount of consumed oxygen. The behavior of S. araneus were recorded on video to assess whether there are differences in their activity is seasonal.