Persisting clone pool differences in sexual/asexual Buchholzia appendiculata (Enchytraeidae, Oligochaeta) as revealed by genetic markers

Clonal variation in the diploid sexual/asexual Buchholzia appendiculata was studied in an isolated area of the bog Langstrup Mose, Northern Zealand. Based upon the electrophoretic variation offered by three di-allelic loci (GPI, MDH and PGM) the distribution of genetically distinct clones was followed from 1987 until 1998 in a Central area where 5-10 % of the individuals reproduced sexually in 1987 and 1988 and two opposing Marginal areas where sexually mature individuals were never observed indicating propagation exclusively through transverse fragmentation, which is the predominant mode of reproduction in this species. Clonal diversity as measured by Simpson's index was significantly higher in the Central area than in the two Marginal areas. This situation remained constant throughout the observational period and with no trend towards a more uniform distribution of clones. Similarly, three major clones present in all observations showed significant differences in mean frequencies between areas, and these differences also remained constant. Taking into account the short distances (5-10 m) between sampling areas and the long observational period this indicates a remarkably stable situation. The ultimate reason(s) for this stability remains unclarified but it may indicate either an extremely low dispersal rate in Buchholzsia appendiculata or perhaps differential mortality in a heterogenous environment.