THE MARINE SNAIL, CERITHIDEA-CALIFORNICA, MATURES AT SMALLER SIZES WERE PARASITISM IS HIGH

I investigated life-history and parasitism in the salt marsh snail, Ce rithidea californica Latitude and growing conditions were important fa ctors determining maturation size. After accounting for environmental variation, there was a negative association between the maturation siz e of snails and the prevalence of parasitic castration by larval trema todes. As predicted by life-history theory, this may represent an adap tation against parasitism that is similar to previous observations of life-history adaptations in species subject to predation or disturbanc e. However, it was unclear whether this adaptation was due to phenotyp ic plasticity or genetic differences among populations resulting from natural selection so I conducted a reciprocal transplant between sites with high and low prevalence and found source population differences in maturation size. It appears, therefore, that the life-history diffe rences between.these populations are at least partially genetic or may represent an adaptive developmental switch that was initiate prior to the transplant.