Temporal Allozyme Divergence in Infrapopulations of the Hemiurid Fluke Lecithochirium fusiforme

The effect of time on genetic differentiation was studied among infrapopulations of mature specimens of the hemiurid fluke, Lecithochirium fusiforme, a parasite of marine fishes. Genetic distances and genetic structure within and among different temporal samples of a geographical population were investigated using starch gel electrophoresis, by screening 6 polymorphic loci in 2 groups of infrapopulations corresponding to different sampling data, i.e., winter 1997–1998 and autumn 1998. The genetic distance among infrapopulations was low (D = 0.000–0.058 ± 0.041). However, genetic divergence among infrapopulations from the same geographic location was clearly lower within each temporal sample (G_ST = 0.021 and 0.034) than the corresponding value obtained for 12 infrapopulations sampled at different seasons of the year (G_ST = 0.067). These results suggest the existence of a relatively important temporal effect that accounts for the differences in genetic variability among adult infrapopulations of L. fusiforme. Therefore, a hypothetical temporal gene flow favored by the existence of persistent life-cycle stages of this species in paratenic hosts is not sufficient to mask the temporal differentiation caused by genetic drift.