title: Phylogenetically Widespread Polyembryony in Cyclostome Bryozoans and the Protracted Asynchronous Release of Clonal Brood-Mates.
abstract: Polyembryony-the production of multiple cloned embryos from a single fertilised egg-is a seemingly paradoxical combination of reproductive modes that nevertheless persists in diverse taxa. We document features of polyembryony in the Cyclostomata (Bryozoa)-an ancient order of modular colonial marine invertebrates-that suggest a substantial reduction in the paradoxical nature of this enigmatic reproductive mode. Firstly, we provide molecular evidence for polyembryony in three exemplar species, supporting the widely cited inference that polyembryony characterises the entire order. Secondly, genotyping demonstrates protracted release of cloned offspring from the primary embryo in a given gonozooid (chamber for embryonic incubation), thus exposing the same genotype to changing environmental conditions over time. Finally, we confirm that each gonozooid produces a distinct genotype, with each primary embryo being the result of a separate fertilisation event. We hypothesise that the sustained release of one or a few genotypes against varying environmental conditions achieves levels of risk-spreading similar to those in organisms that release multiple, unique genotypes at a single time. We argue that polyembryony, specifically with the production of a large number of progeny per fertilisation event, has been favoured in the Cyclostomata over long geological periods.
authors.affiliation: Marine Biological Association of the United Kingdom, Plymouth, Devon, United Kingdom.|Department of Life Sciences, Natural History Museum, London, United Kingdom.|School of Biological Sciences, Bangor University, Bangor, Gwynedd, United Kingdom.
authors.forename: Helen L
authors.initials: HL
authors.lastname: Jenkins
authors.affiliation: Department of Life Sciences, Natural History Museum, London, United Kingdom.
authors.forename: Andrea
authors.initials: A
authors.lastname: Waeschenbach
authors.affiliation: Department of Life Sciences, Natural History Museum, London, United Kingdom.
authors.forename: Beth
authors.initials: B
authors.lastname: Okamura
authors.affiliation: School of Biological Sciences, Bangor University, Bangor, Gwynedd, United Kingdom.
authors.forename: Roger N
authors.initials: RN
authors.lastname: Hughes
authors.affiliation: Marine Biological Association of the United Kingdom, Plymouth, Devon, United Kingdom.
authors.forename: John D D
authors.initials: JD
authors.lastname: Bishop
mesh_terms: D000818:Animals; D002013:Bryozoa / Q000196:embryology* / Q000235:genetics*; D002999:Clone Cells; D019976:Cloning, Organism; D005838:Genotype; D010802:Phylogeny; D012098:Reproduction / Q000235:genetics*