GENETIC EGG AND CLUTCH SIZE VARIATIONS IN FRESH-WATER PRAWN POPULATIONS

I examined the genetic basis of different egg and clutch sizes in two populations of the freshwater prawn Macrobrachium nipponense inhabiting a single water system, by reciprocal crossings in the laboratory. The male and female intercrossed without any obstacle and produced viable F1 hybrids. The hybrids exhibited intermediate phenotype of egg and clutch sizes between the parental values, suggesting that these reproductive traits are controlled by a quantitative genetic system. The genetic control on egg size seemed to be strict, while that on clutch size was weak. Since viability and fertility did not decline in the F1 hybrids, it is unlikely that these post-mating factors operate as the major cause of reproductive isolation between the two groups of individuals in the field. I suggest that the variation in reproductive traits among local populations of this species is. despite the possibility of dispersal in pelagic larvae, principally enabled by the discontinuity of habitat.