CLIMATIC CORRELATES OF CHROMOSOMAL VARIATION IN THE AFRICAN VLEI RAT,OTOMYS-IRRORATUS

The distribution of four chromosomal races of vlei rats Otomys irrorat us in South Africa was found to be significantly correlated with clima te. Cytotype distributions corresponded closely with recognised climat ic regions. In particular, the distribution of a reproductively-isolat ed chromosomal race bearing a tandem fusion rearrangement corresponded with the limits of the Drakensberg Mountain Range. A multivariate ana lysis of 13 climatic variables in 17 populations of known karyotype wa s undertaken. Principal component analysis failed to group cytotypes a ccording to climate; however, complete climatic separation of populati on into cytotype groups was achieved using discriminant analysis. Vari ables describing climatic extremes were more important in discriminati ng between cytotypes than variables describing mean values. Cytotypes varied mainly in the number of heterochromatic arms. There was a posit ive correlation between the relative amount of heterochromatin in the karyotype and climatic aridity/unpredictability. The role of the amoun t and genomic location of heterochromatin in increasing variation of g ene regulation in heterogeneous environments was discussed.