On the Question of Hybridization and Variation in the Oligochaete Genus Limnodrilus

Abstract

Variant forms of Limnodrilus are common in many ecosystems in North America. The question of whether these variant forms are ecomorphs or hybrids of two local species has not been substantiated. In an attempt to determine the relationship of variant Limnodrilus to typical species, the length of the penis tube, minimum diameter of the shaft, and maximum diameter of the shaft were measured on numerous individuals of L. hoffmeisteri, L. claparedeianus, L. spiralis, and L. hoffmeisteri (variant) from several geographical areas in North America. The Limnodrilus were collected from Lake Okanagan, Lake Winnipeg, Lake Superior, Lake Huron, Lake Ontario, and the Potomac River. These measurements were used to develop frequency histograms and bivariate scatter plots to illustrate the relationship of the selected species of Limnodrilus. Multivariate discriminant analysis was also used to further test the separation of L. spiralis and L. hoffmeisteri (variant) from the typical forms. Results indicate that L. hoffmeisteri (variant) is indeed an ecomorph of L. hoffmeisteri, and L. spiralis exhibits characteristics of both L. hoffmeisteri and L. claparedeianus but is also most likely an ecomorph of L. hoffmeisteri.