Vitellogenic mechanisms and the allocation of energy to offspring in polychaetes

Polychaetes show great diversity with respect to ovarian morphology, mechanisms of vitellogenesis and the types of yolk stored in their eggs. This diversity probably reflects interspecific differences in the role of yolk during larval development. Because of the limited number of species investigated and the relatively recent use of analytical techniques, little is known of the origins and chemistry of yolk in polychaete eggs although vitellogenic mechanisms are probably very species specific. There is no apparent relationship between vitellogenic mechanism and egg size and resulting larval developmental mode and while wide intraspecific variation in fecundity has been reported, variation in egg volume and larval mode is uncommon. Ultrastructural studies of vitellogenesis and yolk morphology in the eggs of sibling species of Capitella and populations of Streblospio having different egg sizes and developmental modes, have shown quantitative and perhaps qualitative differences which suggest differences in the energy requirements of the larvae. The significance of interspecific variation in vitellogenic pathways and egg yolk stores to the larval biology of polychaetes remains unclear and awaits further investigation.