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Marine Ecology Progress Series

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MEPS 430:113-119 (2011)  -  DOI:

Does sperm supply limit the number of broods ­produced by a polyembryonous bryozoan?

Andrew J. Pemberton1, Lars J. Hansson1,2, John D. D. Bishop1,*

1Marine Biological Association of the UK, Citadel Hill Laboratory, Plymouth PL1 2PB, UK
2Present address: Department of Marine Ecology, University of Göteborg, 40530 Göteborg, Sweden
*Corresponding author. Email:

ABSTRACT: Polyembryony, the splitting of a single sexually produced embryo into many clonal copies, seems to involve a disadvantageous combination of sexual and asexual reproduction, but persists in a diverse range of organisms. It has been suggested that embryonic cloning in cyclostome bryo­zoans (colonial, sessile marine invertebrates that mate by the release, dispersal and uptake of water-borne sperm) may be a response to sperm limitation. The cyclostome Crisia denticulata inhabits subtidal rock overhangs. Cloned larvae are produced by a colony in a series of independent brood chambers (gonozooids). Offspring from different brood chambers are genetically distinct and are, thus, the outcome of separate fertilisations. We investigated the possibility that sperm limitation reduced female reproductive success at low population density, by assessing the relationship between local colony density, as a proxy for sperm supply, and the number of brood chambers possessed by colonies, as a proxy for fertilisation success. In the patchily distributed population of C. denticulata we studied, the number of brood chambers varied enormously between colonies of the same size, and large colonies entirely lacking brood chambers were frequent, suggesting the occurrence of low fertilisation success within many colonies. However, in colonies with broods, only 17% of the variation in the number of broods per colony could be explained jointly by colony weight and local population density score, with population density being a non-significant predictor in the model. This suggests that sperm supply, as such, does not strongly influence female reproductive ­success and may, therefore, not be important for the maintenance of polyembryony, at least in the studied population. The wide variation in allocation to female function still requires explanation.

KEY WORDS: Sex allocation · Polyembryony · Sperm limitation · Population density · Bryozoa · Crisia

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Cite this article as: Pemberton AJ, Hansson LJ, Bishop JDD (2011) Does sperm supply limit the number of broods ­produced by a polyembryonous bryozoan? Mar Ecol Prog Ser 430:113-119.

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