Genetic Variation of Two Freshwater Snails, Semisulcospira libertina and S. reiniana and Their Presumed Hybrid, in Iga Basin, Mie Prefecture

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  • 三重県伊賀地方でみられるカワニナとチリメンカワニナの酵素多型と雑種型個体
  • ミエケン イガ チホウ デ ミラレル カワニナ ト チリメンカワニナ ノ コウ

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Morphological features of adult and embryo shell and genetic variations of Semisulcospira libertina and S. reiniana were examined from 14 locations in Iga Basin. Two species were detected in 5 populations and only either one species in other 9 populations. In the populations which composed of either single species, adult shells were smooth in S. libertina, and usually ribbed in S. reiniana. The mother snails (25-30 mm in shell height) of S. libertina have 300-700 embryos per individual in winter and the embryo shells were mostly smooth and ranging 1.0-1.8 mm in maximum shell height. In S. reiniana, number of embryos per mother (25-30 mm in shell height) were 170 in winter. Embryo shells were mostly ribbed and larger than in S. libertina, ranging 2.3 mm in maximum shell height. To evaluate genetic variability between populations of these two closely related snail species, two allozymes were examined by starch gel electrophoresis. Marked difference in allele frequencies between the two species was observed at the MPI locus (Mannose phosphate isomerase). Three alleles were estimated at the Mpi^* locus. Those of S. libertina were fixed for the alleles ^*a and ^*a', while that of S. reiniana was for ^*b. The alleles at the locus of Pgm-1^* (Phosphoglucomutase) were highly variable in S. libertina, but less in those of S. reiniana. Population divergency in shell character in two species was correlated to genetic divergency in allopatric populations. By using MPI zymogram pattern, we could identify individuals of two species S. libertina, S. reiniana and their presumed hybrid in the Shourenji and Murou River where those had been difficult to be discriminated from each other by morphological character of adult or embryo shells. In the Tsuchiyahara population which composed of both species and hybrid type, adult snails have mostly smooth shells. Embryo characters exhibited an intermediate feature in MPI type of S. reiniana and MPI hybrid types, but, MPI type of S. libertina had the same embryo character as the allopatric population. While, the hybrid type was not observed in other two sympatric populations. In the Inagu population which included two species but not hybrid, most adult snails had smooth shells, but, embryos showed characters of respective species.

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