Molecular genetic evidence for the prevalence of outcrossing in the hermaphroditic brooding bryozoan Celleporella hyalina

The occurrence of inbreeding was investigated in Celleporella hyalina, whic h has been reported as being capable of selfing. In total, 4 tetranucleotid e microsatellite markers were scored in populations from sites within the M enai Strait (Wales) and the Yealm Estuary (Plymouth, England). All loci in all populations were in Hardy-Weinberg equilibrium, with insignificant Fi, values, which indicates that C. hyalina in these populations generally outb reed. No significant differences were found between populations up to 8 km apart, indicating sufficient gene flow on this scale to form a single breed ing population despite geographic separation. The Plymouth population was s ignificantly (p < 0.00001) deviant from the others, indicating possible iso lation by distance at the scale of 900 km. C. hyalina cultured in the labor atory were observed to spawn sperm into the surrounding seawater. Sib larva e were found to settle randomly with respect to each other. In isolation C. hyalina failed to produce offspring, though a small proportion brooded abo rtive embryos. Pairings between individuals of differing genotypes resulted in the production of offspring, all of which, when genotyped with respect to the parent colonies, were found to be the result of outcrossing.