[Helminth fauna and steroid hormones concentration of wild rodents]

Fragmentation of the environment by natural barriers (lakes, mountain ranges) and human activities (towns, major roads, agriculture) can lead to isolate subpopulations of hosts. The study was based in Mazury lake district in north-eastern Poland, the region rich in forests, lakes, rivers and canals, which can create impassable barriers. Population of bank voles (Clethrionomys glareolus)--dominant woodland rodent--showed local differences in helminth communities in fragmented forest habitat. The sites were chosen on the basis of the similarity of their habitat structure and type, and isolation from one another. There are evidences that steroids hormones associated with stress and reproduction may mediate trade-offs between physiology and immune function.