Heterogeneous population growth, parental effects and genotype–environment interactions of a marine oligochaete

Abstract

Cultures of asexually reproducing populations of the oligochaete Paranaislitoralis (Müller) collected from six different patches (3 to 50 m apart) on an intertidal mud flat in Flax Pond, New York, on two occasions, June and October 1993, showed significant differences among lines in life span, number of offspring produced, and in finite rate of increase (λ). Although growth rates were significantly lower in October than in June, they were always positive (λ > 1) in the laboratory cultures reared in field-collected sediment, while field data show 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 individuals were irreversible: worms from late (declining) stages of population growth had a significantly higher mortality and lower reproduction than worms from earlier stages, also when transferred to high-quality food. Genetical analysis using RAPDs (random amplified polymorphic DNA) confirmed the existence of several clones of P. litoralis in our cultures. Experiments where parent and offspring were cultured in sediments of different qualities showed clone–environment interactions in the number of asexual offspring produced, but not in age at first reproduction. Clones also differed in that some showed significant parental effects of sediment quality on life-history characteristics while other clones did not. Our results indicate that P.litoralis populations in Flax Pond are not an example of a population subdivided into a set of permanent source and sink subpopulations, but rather an example of a continuously shifting mosaic of local growth conditions.