Premating and Postmating Isolation among Local Populations of Freshwater Shrimp Palaemon paucidens in Japan

The levels of reproductive isolation between the local populations of the freshwater shrimp Palaemon paucidens in Japan, were estimated on the basis of mating experiments. Postmating isolation has been clearly observed between the A- and B-types which are genetically differentiated based on isozymic analysis. A higher level of premating isolation has been observed between local populations within the A-type, inhabiting ponds and upperstream of rivers. No premating isolation has been observed among different local populations in the B-type, inhabiting downstream or estuarine area. The levels of reproductive isolation are related to the level of genetic differentiation obtained from the different genetic distances.