GENETIC VARIATION IN POPULATIONS OF THE HERMAPHRODITIC FLATWORM MESOSTOMA LINGUA (TURBELLARIA, RHABDOCOELA)

¹ Biology Department, University of Windsor, Windsor, Ontario, Canada N9B 3P4

Populations of the rhabdocoel Mesostoma lingua at a site in the Canadian arctic were polymorphic at two often allozyme loci. Phenotypic frequencies were determined in more than 1500 individuals from 35 populations at the polymorphic loci phosphoglucomutase and mannose-6-phosphate isomerase. Considerable gene frequency divergence was noted between populations only a few meters apart indicating that gene flow is low. Inbreeding coefficients due to population subdivision averaged 0.15, suggesting that existing populations receive an average of only one new migrant per generation. Genotypic frequencies in individual populations were ordinarily in good agreement with Hardy-Weinberg expectations, revealing that this hermaphroditic organism does not engage in self-fertilization.