AN ECOLOGICAL COMPARISON BETWEEN STANDARD AND CHROMOSOMALLY DIVERGENTHOUSE MICE IN NORTHERN SCOTLAND

In western Europe there are populations of the house mouse that diverg e in karyotype from the standard 40-chromosome complement as a result of Robertsonian fusions between pairs of chromosomes. Very little is k nown about the ecology of such Robertsonian populations of the house m ouse. The present study focuses on the Robertsonian system of north ea st Scotland. We distinguish seven ''chromosomal zones'' along north-so uth and east-west transects (2 n = 32 in the extreme north east, 2 n = 34 S(outh), 2 n = 34 W(est), 2 n = 36 S, 2 n = 36 W, 2 n = 40 S, 2 n = 40 W). We describe and compare the different chromosomal zones in re lation to their habitat and population characteristics. The 2 n = 32 c hromosomal race is characterised by the lowest density as well as the lowest frequency of pregnant and lactating females. The highest densit ies are found in both the 2 n = 40 zones. Intermediate chromosomal zon es appear to be separated from each other by habitat where the house m ouse does not occur. Thus, passive transport may represent the only me ans by which mice could move between zones. Within the 32, 34 and 36 S zones movements of materials occur, while farmers from these areas ha ve few, if any, interactions with farmers in the other zones. This pat tern of agricultural contact would tend to facilitate chromosomal flow between the 32, 34 and 36 S chromosomal zones and isolate them from t he three other zones. Chromosomal flow between the 32 zone and adjacen t areas may threaten the low-density, low-fertility 32-chromosome race with extinction.