GENETIC-DIVERGENCE BETWEEN THE SIBLING SPECIES OF RIVER-SCULPIN, COTTUS-AMBLYSTOMOPSIS AND COTTUS-NOZAWAE, WITH SPECIAL REFERENCE TO SPECIATION

Polypatric speciation from an amphidromous ancestor has been suggested for a fluvial goby Rhinogobius flumineus; a similar history may explain life-history and genetic variation in Cottus species. We used starch-gel electrophoresis to examine intra- and interspecific genetic differentiation of two sibling Cottus species, amphidromous C. amblystomopsis and fluvial C. nozawae, which are presumed to be in an ancestor-descendant phyletic relationship. Genetic differentiation was markedly less within C. amblystomopsis, than in C. nozawae. One group of C. nozawae populations was closer to C. amblystomopsis (by Nei's genetic distance) than it was to other populations of C. nozawae. This suggests that the differentiation of presently identifiable groups of C. nozawae populations might have occurred polypatrically from an amphidromous ancestral population at different times. The two groups are presumed to be different species in spite of their quite similar morphological and ecological characteristics: we propose to call this type of speciation 'Polypatric and parallel speciation'. This model of 'Polypatric and parallel speciation' might be generalized to explain evolution of amphidromous or anadromous species to fluvial or lacustrine land-locked species. © 1990 Kluwer Academic Publishers.