Genetic variation in coexisting sexual diploid and parthenogenetic triploid Trichoniscus pusillus (Isopoda, Crustacea)

In an area where sexual diploid and parthenogenetic triploid forms of Trichoniscus pusillus coexist in varying proportions, the populations were studied for eight different loci. Four loci were monomorphic and identical, one was monomorphic but differed in the two forms, three were polymorphic and, at the same time, without alleles common to the two forms. In one of the latter loci (Pgm) both diploid and triploid populations showed constant differential distributions of genotypes within the area studied. Comparisons of coexisting populations in 13 stations revealed parallel trends in the distribution of Pgm genotypes in diploids and triploids. This indicates that the variation is adaptive within both forms. There is, however, no correlation between the adaptive variation within diploids and triploids and the environmental factor(s) underlying the distribution of the two forms. This is taken to indicate an uncoupling of micro- and macroevolutionary processes.