KUPRIYANOVA, E.K.; University of Adelaide, Australia: Browsing through old journals: lessons learned from earlier fecundity-time models

In 1973 Vance published a model that explains differences in reproductive strategies in marine invertebrates. The original model (Vance 1973a) resulted in a concave fitness function suggesting that only extremes of egg provisioning (referred to as egg size) are evolutionary stable. The results of the Vance model are believed to be validated by other models that independently predict evolutionary stability of extreme egg sizes. This has been commonly interpreted as a proof that the Vance model, albeit oversimplified, reflects the fundamental evolutionary principle of disruptive egg size evolution in marine invertebrates. However, empirical studies of the last several decades illustrate that intermediate levels of egg provisioning are widely observed in nature. Only the recent modifications of the original Vance model attempt to expain evolution of such intermediate strategies: McEdward (1997) does so by incorporating the effects of facultative feeding, whereas Levitan (2000) model uses inverse rather than linear relationship between egg size and development. Critical re-examination of the earlier fecundity-time models of the “Vance family” gave unexpected results: it showed that only Vance (1973a) and its minor modification by Grant (1983) invariably predict evolutionary stability of extreme egg sizes, while most modifications of Vance (1973a) model can in fact predict at least some intermediate reproductive strategies.