Long-term isozyme variation in parthenogenetic polyploid forms of Lumbricillus lineatus (Enchytraeidae, Oligochaeta) in recently established environments

Abstract

Polymorphism in the phosphoglucomutase and phosphoglucose isomerase loci was studied throughout several generations in parthenogenetic tri-, tetra- and pentaploid forms of Lumbricillus lineatus, occurring in the littoral zone along two canals connecting brackish fjords with the saline North Sea. Tetra- and pentaploids have not been found outside these restricted localities which are characterized by strong variations in salinity. It is supposed that spermatozoa produced by the tetra- and pentaploids activate the parthenogenetic eggs of all three biotypes. Restoration in the parthenogenetic eggs is of the ameiotic type. In spite of that only a moderate degree of heterozygosity was observed. More than one genetic variant were constantly present among tri- and tetraploids. A heterogeneous niche is proposed to account for the polymorphism observed. Both seasonal variations and long-term changes in the frequency of genotypes indicate a certain degree of evolutionary flexibility in these parthenogenetic organisms.