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Marine Ecology Progress Series

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MEPS 120:193-201 (1995)  -  doi:10.3354/meps120193

Environmental and genetic components of variation in sexual allocation by an epialgal bryozoan

Hunter, E., Hughes, R. N.

Celleporella hyalina colonies growing on Fucus serratus were collected from the field and induced to release larvae in the laboratory. From these larvae, colonies were established on glass slides and each cloned by fragmentation. Growth and sexual activity of genotypic replicates in each of 4 environments were monitored for 12 wk. The environments, representing seasonal contrasts in the field, were created from the 4 combinations of lower/higher temperature and lower/higher food supply. Growth, measured as the production of basal autozooids (responsible for feeding), and sexual activity, measured separately as the production of basal male, frontal male and female zooids, were significantly affected by genotype and environment. Genotypes differed in colonial growth rate and in the numbers of male and female zooids produced per colony. Within genotypes, growth was fastest at higher temperature and food supply. Higher food supply encouraged the production of autozooids and sexual zooids. Higher temperature strongly encouraged female production, but not male. Male production was greatest at higher food supply combined with lower temperature, when female production was very low. Colonies maturing in 'summer' conditions therefore invested heavily in females whereas those maturing in 'winter' conditions invested heavily in males. This phenotypic response might promote fitness by ensuring that quantities of females are not produced under environmental conditions that would prolong embryogenesis and brooding beyond a critical time limit set by risks of colonial mortality. On the other hand, overlapping generations and sperm storage would provide opportunity for cross fertilization even during winter, when it would pay to invest in males. The genetically based component of variation in sexual allocation in C. hyalina may reflect polymorphism sustained by varying mating opportunities.

Celleporella hyalina . Simultaneous hermaphrodite . Clones . Sex allocation . Temperature . Food

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