Chromosome and Enzyme Variation of Hydrotaea Irritans (Fallen) (Diptera: Muscidae)

Abstract

The analysis of metaphases from the brain of third instar larvae from flies caught in the Netherlands revealed numbers of chromosomes ranging from 12 to 15. Of these, five pairs of large metacentric and submetacentric chromosomes were common to all individuals, so the number of supernumerous chromosomes varied from 2 to 5. In an ongoing study of variation in chromosome number of flies caught in Denmark, we found two common types each with 12 and one rare type with 11 chromosomes in forest flies. In the majority of flies from nearby pastures, we counted 13 or 14 chromosomes, but larvae with 12 or 11 chromosomes were also found.

Variation in isozyme frequencies was investigated by electrophoresis in populations from several locations in Jutland (Denmark). Each locality was represented by a sample from a forest area and a nearby pasture. The data revealed a peculiar banding pattern at four enzyme loci.The occurrence of certain presumed heteroxygous bands at one of these loci was linked to the occurrence of certain other presumed heterozygous bands at the other three loci. Despite rather high frequencies of such “heterotypes”, at least in some samples, one of the corresponding homozygote types was never observed. The banding pattern at another polymorphic locus was independent of the occurrence of “heterotypes”.

Possible hypotheses to explain the observed pattern of variation are discussed.