HYBRIDIZATION OF CHROMOSOME-POLYMORPHIC POPULATIONS OF THE INQUILINE ANT, DORONOMYRMEX-KUTTERI (HYM, FORMICIDAE)

The workerless, inquiline ant, Doronomyrmex kutteri has isolated populations with a haploid chromosome number of n = 23 both in the Alps (Swiss and South Tyrolean Alps) and in Sweden, and a population with n = 25 in southern Germany. Crossbreeding of sexuals from all populations proved successful. Backcrosses of F 1-females with males from the parental populations produced F 2-females, and hybrid males with n = 23, 24, or 25 chromosomes. The chromosome polymorphism is not due to B-chromosomes. Probably the n = 25 karyotype originated from the n = 23 karyotype by two Robertsonian fissions (2 MBAR --> 4 ABAR), since the n = 25 karyotype was found in only one of the populations. Diploid males occurred frequently in colonies from four out of five sites investigated.