Oogenic strategies in the evolution of development in Patiriella (Echinodermata : Asteroidea)

The sea star genus Patiriella has the greatest diversity of life histories known for the Asteroidea, P. regularis has small eggs (150 mu m diameter) a nd the ancestral planktotrophic larvae. P. calcar, P. gunnii, P. exigua and P. pseudoexigua have large eggs (390-440 mu m diameter) and non-feeding le cithotrophic larvae. Two species with lecithotrophic larvae P. vivipara and P. parvivipara have secondarily evolved a small egg (135-150 mu m diameter ). We examined the oogenic strategies involved with evolution of egg size i n these sea stars. Comparison of protein profiles, histochemistry and ultra structure of the eggs of Patiriella indicated that the major changes underl ying acquisition of a large egg involved enhanced deposition of lipid in so me species and an increase in yolk reserves in others. The eggs of the plan ktotroph, P. regularis, and the benthic lecithotroph, P. exigua, contained an abundance of major yolk protein MYP. By contrast, the eggs of the plankt onic lecithotrophs P. gunnii and P, calcar were dominated by lipid and the MYP appeared to be greatly reduced. The eggs of P. calcar contained an abun dant protein which may be a truncated form of vitellogen. The small eggs of the viviparous species P. vivipara and P. parvivipara appear to be miniatu re versions of the eggs of the closely related P. exigua. Comparison of the eggs of Patiriella species with lecithotrophic development revealed among species variation in oogenesis, Depending on the species, the evolutionary modification of oogenesis appeared to be influenced by phylogenetic history and selection for egg characteristics with respect to the planktonic or be nthic location of development.