Effect of cloning rate on fitness-related traits in two marine hydroids
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Hydractinia symbiolongicarpus and Podocoryna carnea are colonial marine hydroids capable of reproducing both sexually and asexually. Asexual reproduction, by colony fragmentation, produces a genetic clone of the parent colony. This study examines the effect of extreme cloning rates on colony growth rate, oxygen uptake rate, and colony morphology. Colonies of both species maintained for an extended period of time in a state of constant vegetative growth by repeated cloning (“growing” colonies) grew more slowly than genetically equal replicates which were restricted from vegetative growth and underwent no cloning (“restricted” colonies). For one species, the growing colonies used oxygen at a higher rate; for the other species, no difference was detected, although the sample size was small. A difference in colony morphology was found, with the restricted colonies exhibiting a more “sheet-like” shape, while their growing counterparts appeared more “runnerlike.” Subsequent to these experiments, in the third winter of treatment, all colonies experienced a severe tissue regression. Within 6 months after this event, the colonies had regrown to their former sizes. A growth assay at this point revealed no difference in growth rate, suggesting an epigenetic basis for these results.