Genetic variation within and among infrapopulations of the marine digenetic trematode Lecithochirium fusiforme

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Abstract
Allozyme markers were used to study genetic variation in Lecithochirium fusiforme within a natural population of Conger conger. Six of 16 enzyme-coding loci studied were found to be polymorphic. These loci were surveyed in 12 infrapopulations of adult flukes. High levels of genetic variation were detected (P=0·375); Ho=0·048; He=0·085). However, the population did not conform to Hardy-Weinberg expectations, as it showed a significant deficit of heterozygotes. L. fusiforme also exhibited low differentiation between infrapopulations (FST=0·064). Despite significant linkage disequilibrium at Pgm-1 and Pgm-2 (PFIS and FST statistics suggests the existence of the Wahlund effect. However, all infrapopulations showed a strong deficit of heterozygotes for most polymorphic loci (FIS=0·409). Detection of significant genetic differentiation among temporal samples and the existence of paratenic hosts in the life-cycle suggests the Wahlund effect, caused by the mixture of genetically distinct temporal samples in the infrapopulations. Occasional temporal gene flow also might explain the high estimated genetic polymorphism.

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