Relative investment in offspring by sessile Rotifera

Abstract

Correlations of egg and body volumes of 65 species of oviparous Rotifera from the three families of sessile rotifers (Atrochidae, Collothecidae, Flosculariidae) were determined from size measurements documented in the literature and from unpublished data (RLW). While egg volume (EV) of amictic (subitaneous) eggs increased as a function of body volume (BV) in these families, relative egg volume (REV) decreased with increasing BV indicating that relative investment per offspring is less in larger-bodied species. Regression coefficients for REV as a function of BV for these families were significantly different from each other and that of the strictly planktonic species studied by Walz et al. (1995). Thus, our statistical analysis indicates that relative investment per offspring was greatest in planktonic species, intermediate in Flosculariidae, and lowest in Collothecidae. These results suggest that the sessile families do not follow the standard pattern of EV predicted for planktotrophic and lecithotrophic larvae as is found in many marine benthic invertebrates.