McNab’s “Resource Rule” and adaptive changes in the skull of the common shrew (Sorex araneus L., Eulipotyphla, Soricidae) from different ecosystems

Adaptive features of the skull were compared with the resource of soil macrofauna in populations of three monomorphic chromosomal races of the common shrew from different ecosystems. In the severe climatic conditions of the shrubby tundra of the Vorkuta area (67°29ʹ N), with extremely low abundance of large oligochaetes (earthworms), the population of the Serov race is characterized by small sizes of the skull and brain capsule, a relatively short arm of the temporal muscle strength, a weak jaw compression force therefore being likely. In the tundra ecosystem, McNab’s “resource rule” is confirmed while Bergman’s rule (optimization of metabolism by a relative reduction of the body surface area) is violated. In the severe climatic conditions of the mountainous areas of the northern taiga in the northern Urals (62°05ʹ N, 520– 650 m above sea level), with high numbers of earthworms, the Serov race is characterized by large sizes of both skull and brain capsule, a lengthened temporal muscle force arm, therefore, increased temporal muscle mass and jaw compression force thus being likely and corresponding to McNab’s “resource rule” and Bergman’s rule. In spruce-broadleaved forests between the Upper Volga River area and Oka River (55°44ʹ N) with high abundance of earthworms, small sizes of the skull and brain capsule are characteristic of the Moscow race, the force of jaw compression being increased by an increase in the arm of temporal muscle strength. Under the best climatic conditions, a decreased size of the Moscow race is consistent with Bergman’s rule and violates McNabb’s “resource rule”. The results of the study show that climatic conditions are capable of directly affecting the body size of shrews, not only indirectly through the productivity of the environment, thus confirming Bergman’s rule.