Predation and Rate of Evolution in Cyclomorphic Daphnia

Summary

1.	Since fish prey selectively on zooplankton, different phenotypes of cyclomorphic Daphnia goleata mendotae may be differentially selected for during summer months.
2.	In selection experiments high-helmeted forms survived better than did short-helmeted forms.
3.	Even if low adaptive values with respect to escapability from predators are assumed, in parthenogenetic populations the genotype composition will rapidly shift in favour of the best escapers.
4.	Genotypic uniformity will soon result unless special mechanisms insure genetic diversity. The possibilities of intra-clonal diversity and seasonal fluctuations of adaptive values are discussed.