Genetic Structure of Populations of the Earthworm Aporrectodea tuberculata

Abstract

Electrophoresis of enzymes was employed to analyze the genetic structure of populations of the earthworm Aporrectodea tuberculata (Lumbricidae) in the vicinity of Rochester, New York, where 30 local collections were made in deciduous woods and fallow agricultural fields in five regions. Individual allozyme (electromorph) phenotypes at six polymorphic enzyme loci were scored, and F-statistics were used to estimate variances of allele frequencies associated with demes, habitats, and regions. Populations of A. tuberculata are highly polymorphic, the breeding system is amphimictic, and mating apparently is random within plots 10 m2 in area. Demes within habitats were mildly differentiated (mean standardized variance over loci, FDA, was 0.0268), and interhabitat differences within regions were only slightly larger (FHR = 0.0342). There was little geographic variation, FRT being only 0.0178. Much or all of the genetic differentiation within and between habitats in regions can be attributed to historical demographic processes, including founder effects and sampling drift in semi-isolated demes or as a consequence of isolation by distance. This interpretation is supported by the general homogeneity of variance estimates for the six loci, and by the absence of associations of allele frequencies with habitat types. Migration between the very large populations maintained by A. tuberculata apparently is sufficient to prevent the development of strong local and regional differentiation that might otherwise occur through genetic drift and selection.