Intraspecific variation in larval size and its effects on juvenile lophophore size in four bryozoans

Abstract

The quantity of maternal investment per offspring is related to maternal fitness and offspring performance. Some models suggest that maximum maternal fitness occurs when mothers produce offspring of a single optimal size (size being a proxy of maternal investment). However, there is substantial intraspecific variation in offspring size, especially in species with lecithotrophic larvae. For most species, the level at which this variation occurs (within vs. among brood) is unclear. We quantified variation in larval size within and among broods for 4 species of bryozoans with lecithotrophic larvae. Larval size was highly variable in all species, and the majority of the variation was found within broods for 3 of the 4 species. In all 4 species, sibling larvae varied up to 2-fold in volume. Further, there were strong positive relationships between initial larval size and juvenile lophophore size for all 4 species. Lophophore size is related to feeding ability, so variation in larval size may result in variation in feeding ability among sibling juveniles. These results offer a probable mechanism for the positive relationship between initial larval size and colony growth rate in bryo zoans.