[Genetic heterogeneity in natural populations of Microphallus piriformes and M. pygmaeus parthenites (Trematoda: Microphallidae)].

The random amplified polymorphic DNA (RAPD) technique was applied for the studies of genetic heterogeny between several natural populations of trematodes belonging to the Microphallida family. Initially, the metacercariae from the daughter sporocysts infestating Littorina saxatilis and Littorina littorea periwinkles were used. Comparison of the banding patterns obtained for the different metacercariae within one sporocyst gave an unpredicted results. For two of three studied species (M. pygmaeus and M. pseudopygmaeus), the considerable differences in RAPD patterning was detected. According to the classical point of view, the process of cercariae (metacercariae in case of the "pygmaeus" group of microphallides) formation does not include DNA recombination. Because of that, all metacercariae within one single sporocyst should be genetically identical. However, data obtained clearly shows that at least in some cases it is not so. We can hardly believe that such result could be a methodological artifact, for not single difference in a RAPD patterns was recorded between the metacercariae within sporocysts of M. piriformes. Moreover, even the 100 fold dilution of the total DNA used for PCR amplification does not change the banding patterns. Hence, our results can not be explained by slight fluctuations in the DNA concentrations between the samples. The most evident conclusion is that we came across yet strange, but real phenomenon--some degree of genetic difference within the progeny of each of the sporocysts--metacercariae. However, the detailed study is needed to understand and interpret these observations correctly. Amplification of the total DNA extracted from the whole sporocysts (containing metacercariae) never showed any differences in RAPD patterns between the parasites been derived from one infestated snail (local parasite hemipopulation). That allowed us to compare different parasite populations referring the RAPD pattern of one sporocyst from a snail to as a representative of one local hemipopulation. Analysis of the RAPD-loci frequencies showed a considerable genetic differences between the subpopulations of M. piriformes, infestating different paraxenic intermediate hosts--L. saxatilis and L. obtusata. This phenomenon was statistically significant for 2 localities of 3 studied. No heterogeny within populations was recorded for M. pygmaeus. Both M. piriformes and M. pygmaeus are characterized by the genetic differentiation in the microgeographic scale (within the Chupa bay of the White sea, the longest distance between the analyzed localities is 20 km). According to the frequencies of the RAPD-loci, parasites from the sheltered locality differ significantly from the parasites of other two localities exposed to the open sea. For both species the degree of genetic similarity between the populations correlates positively with the distance between the localities. We can suppose that the population structure of microphallids depended mainly upon the population structures of their intermediate hosts, definitive hosts and geographical structure of the areal. However, taking into consideration the low motility of snails, we believe that the distribution, migration and species composition of the definitive hosts play the key role in the genetic structuring of M. pygmaeus and M. piriformes hemipopulations. As an addition, the RAPD analysis of the parasite populations from the Barents Sea (East cost of Murman peninsula) and North Sea (Western cost of Sweden) revealed no significant genetic differences between the worms from those places and from the White Sea. However in case of this macrogeographic comparison, insufficient number of samples does not allow us to draw any final conclusions.