A HYBRID ZONE BETWEEN 2 CHROMOSOME RACES OF THE COMMON SHREW, SOREX-ARANEUS, IN EASTERN POLAND - PRELIMINARY-RESULTS

We established the location of the contact zone between the Drnholec ( diagnostic metacentrics hi, ko, gm, nr) and Bialowieza (hn, ik, gr, mp ) races of the common shrew in eastern Poland. The hybrids in this zon e form meiotic chain configurations consisting of a maximum of 10 elem ents. Moreover, we caught 13 different types of hybrids with shorter c hain complexes, resulting because of a polymorphism for metacentrics k o, nr, gr. The Drnholec/Bialowieza contact zone is stabilized on an en vironmental barrier (a railway embankment). The sharp change in freque ncies of diagnostic metacentrics across the railtrack showed that it w as a strong barrier to migration of the shrews. At present it is diffi cult to say whether there is any mechanism enhancing fertility in the hybrid populations.