MEPS 272:301-305 (2004)  -  doi:10.3354/meps272301

When the going gets rough: effect of maternal size manipulation on larval quality

Dustin J. Marshall1,2,*, Michael J. Keough1

1Department of Zoology, The University of Melbourne, Victoria 3010, Australia 2Present address: School of Biological, Environmental and Earth Sciences, University of New South Wales, New South Wales 2052, Australia

ABSTRACT: Variation in larval size has been shown to be an important factor for the post-metamorphic performance of marine invertebrates but, despite its importance, few sources of this variation have been identified. For a range of taxa, offspring size is positively correlated with maternal size but the reasons for this correlation remain unclear. We halved the size of colonies in the bryozoan Bugula neritina 1 wk prior to reproduction (but during embryogenesis) to determine if larval size is a fixed or plastic trait. We manipulated colonies in such a way that the ratio of feeding zooids to reproductive zooids was constant between treatment and control colonies. We found that manipulating colony size strongly affects larval size; halved colonies produced larvae that were ~13% smaller than those produced by intact colonies. We entered these data into a simple model based on previous work to estimate the likely post-metamorphic consequences of this reduction in larval size. The model predicted that larvae that came from manipulated colonies would suffer ~300% higher post-metamorphic mortality and ~50% lower fecundity as adults. Colonies that are faced with a stress appear to be trading off current offspring fitness to maximize their own long-term fitness and this may explain previous observations of compensatory growth in colonial organisms. This study demonstrates that larval size is a surprisingly dynamic trait and strong links exist between the maternal phenotype and the fitness of the offspring. The performance of settling larvae may be determined not only by their larval experience but also by the experience of their mothers.

KEY WORDS: Offspring size · Maternal effect · Regeneration

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