Asexual reproduction and genetic determination of colour patterns within populations of the subtidal sea anemone Anthothoe albocincta

Southeastern Australian populations of the dioecious, subtidal sea anemone Anthothoe albocincta display considerable spatial variation in the colour patterns of the constituent polyps, and the most visually striking feature of local populations are sets of dense aggregations each comprised of polyps with a single colour pattern. We used a combination of genetic data, observations and manipu lative experiments to infer that A. albocincta generates these monomorphic aggregations via asexual reproduction and that asexual reproduction plays the major role in the maintenance of established populations. Allozyme electrophoresis of 2 to 5 polyps from each of 20 mapped aggregations (in 2 populations) revealed that in 18 cases (90 %) all polyps were electrophoretically identical and always distinct from differently coloured polyps taken from each of 26 adjacent aggregations. Furthermore, the genetic structure of each of 13 populations separated by up to 930 km was consistent with the predicted effects of localised asexual recruitment. We detected 16 heterozygote excesses and 11 heterozygote deficits (p < 0.05) in a total of 66 tests for departures from Hardy-Weinberg equilibria. Moreover, each population contained significantly less (p < 0.005) multi-locus genotypic diversity (G(o)) than was expected for a randomly mating population (G(e)) (mean G(o):G(e) = 0.30) and contained relatively few unique 7-locus genotypes. Some genotypes were found within many aggregations, suggesting successful clones may have extensive and discontinuous distributions within populations. In addition, we observed longitudinal fission of adult polyps in both field and laboratory conditions, and found that over a 6 mo period 82% (i.e. 1469 of 1790) of new recruits into 30 experimentally cleared patches, within 3 populations, were morphologically identical to those within surrounding aggregations. These data, together with our earlier analysis of genetic variation among populations, and observations of gonad development, imply that this species uses fission to maintain populations, consisting predominantly of spatially restricted clones (each with an almost unique colour pattern), but uses sexual reproduction to produce widely dispersed colonists.