EFFECT OF POPULATION-DENSITY AND GENOTYPE ON LIFE-HISTORY TRAITS IN THE ROTIFER BRACHIONUS-PLICATILIS MULLER,O.F.

Effects of population density on mictic response and the population dy namics of 13 clones of Brachionus plicatilis were investigated by cult uring isolated females at two different population densities. Results from the experiments did not provide general support for the dependenc e of mictic response on population density. Only six clones, isolated amictic females cultured at a density of 5 females.ml-1, produced high er proportions of mictic female offspring than females grown at a dens ity of 1 female.ml-1, indicating that mictic-female production in thes e clones of B. plicatilis is density-dependent. High population densit y affected other life-history traits: lifespan (e0) and fertility per female lifetime (R0) decreased with density. Interclone differences in the mictic response to density were detected, which may be caused by genetic differences in the capacity to undergo mixis. High variabiliti es for mictic rates and life-table parameters were found among clones derived by selfing from a clone. These results indicate that age of th e parental female is also a significant internal factor that affects t he production of mictic daughters.