Large Genetic Distances Associated with Little Morphological Variation in Polycelis coronata and Dugesia tigrina (Planaria)

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Abstract
Genetic similarities among 22 populations of P. coronata and 1 population of D. tigrina (Planaria) were determined from electrophoretically obtained protein data. Similarity values between populations of Polycelis were lower than expected, being significantly below values reported for many vertebrate and invertebrate species. This difference is partially explained by various ecological and behavioral isolating mechanisms. Lack of morphological variation between populations which does not correspond with the biochemical divergence may imply different rates of evolution at these 2 levels. Evolutionary divergence times based on the protein data are used as possible indices of the migratory pattern of Polycelis in the Pacific Northwest and correlate with the theory of land bridges between North America and Asia.