Clonal Niche Structure in the Parthenogenetic Earthworm Octolasion tyrtaeum

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Abstract
Clones of parthenogenetic species provide an opportunity to study the niches of individual genotypes. O. tyrtaeum, a parthenogenetic earthworm, was collected in Tennessee, North Carolina and New York [USA] in a variety of habitat types differing in soil pH, soil texture and vegetation, which are important niche dimensions for earthworms. Eight genetically distinct clones were identified by starch-gel electrophoresis at 10 structural gene loci. Of these clones 6 were present in only a few collections, and information on their potential niches is limited. The other 2 clones, which were widespread and abundant, are broad-niched and apparently very similar ecologically. In fluctuating environments, selection favors general purpose genotypes, which are relatively insensitive to environmental changes, and which are probably ecologically similar. Because soil and vegetation types form a mosaic pattern, only broad-niched clones can be widespread if dispersal occurs actively through the habitat. If the 2 dominant clones of O. tyrtaeum are nearly identical ecologically, as they may be, competitive exclusion or clonal drift might be expected where they occur together; stable coexistence could result if they differ in their niches.