Parent and larval RAPD fingerprints reveal outcrossing in freshwater bryozoans


  • This paper is the result of ongoing collaborative work to develop and apply novel molecular approaches to population ecology. Cath Jones, formerly supported by the Edward P. Abraham Research Fund, is a Wellcome Fellow in Taxonomy & Systematics working with Les Noble, Research Lecturer in Genetics. Beth Okamura is a University Lecturer in Invertebrate Zoology. Our interests include the evolution of breeding systems and parasite resistance, the ecological maintenance of sex, and the population genetic structure, taxonomy, and systematics of animals capable of uniparental reproduction.

Genetics Laboratory, Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. Tel. 0865 275325/9; fax 0865 275259.


The occurrence of outcrossing in benthic hermaphroditic colonial invertebrates has received much historical debate and little demonstration. Direct genetic study of this question using routine techniques has been limited by both the amount of material required and the detection of adequate DNA polymorphisms. However, the recent development of molecular techniques that require no a-priori sequence data provides new approaches to the characterization of both tiny and genetically similar individuals. Random amplification of polymorphic DNA (the RAPD assay) was used to amplify fragments of DNA (via the polymerase chain reaction) to obtain fingerprints of parental colonies and larval offspring of the hermaphroditic freshwater bryozoan Cristatella mucedo. Here we report the first positive and direct genetic evidence for outcrossing in bryozoans. However, we find that outcrossing generates only low levels of genetic variation in populations that are highly clonal.