HETEROGENEOUS POPULATION-GROWTH, PARENTAL EFFECTS AND GENOTYPE-ENVIRONMENT INTERACTIONS OF A MARINE OLIGOCHAETE

Cultures of asexually reproducing populations of the oligochaete Paran ais litoralis (Muller) collected from six different patches (3 to 50 m apart) on an intertidal mud flat in Flax Pond, New York, on two occas ions, June and October 1993, showed significant differences among line s in life span, number of offspring produced, and in finite rate of in crease (lambda). Although growth rates were significantly lower in Oct ober than in June, they were always positive (lambda > 1) in the labor atory cultures reared in field-collected sediment, while field data sh ow that the densities of P. litoralis decreased sharply in summer and autumn from a seasonal high in early June. Cultures of worms reared at high densities without renewal of sediment crashed, and effects on in dividuals were irreversible: worms from late (declining) stages of pop ulation growth had a significantly higher mortality and lower reproduc tion than worms from earlier stages, also when transferred to high-qua lity food. Genetical analysis using RAPDs (random amplified polymorphi c DNA) confirmed the existence of several clones of P. litoralis in ou r cultures. Experiments where parent and offspring were cultured in se diments of different qualities showed clone-environment interactions i n the number of asexual offspring produced, but not in age at first re production. Clones also differed in that some showed significant paren tal effects of sediment quality on life-history characteristics while other clones did not. Our results indicate that P. litoralis populatio ns in Flax Pond are not an example of a population subdivided into a s et of permanent source and sink subpopulations, but rather an example of a continuously shifting mosaic of local growth conditions.