Workpackage 3: The effect of environmental conditions on the genotypic diversity of cultured rotifers will be determined in stable and variable biotic and abiotic parameters.

In natural rotifer populations, a high genotypic diversity is predicted after population establishment. Clonal selection during the parthenogenetic phase however erodes this diversity (Gómez and Carvalho, 2000). Monogonont rotifers live in habitats that display extensive variation in both biotic and abiotic components. Strong competition promotes reproductive isolation between successive groups of seasonal specialists (King and Serra, 1998). Factor analysis on the limnological parameters recorded during field sampling also indicated that genetically different clonal groups are ecologically specialized (Gómez et al., 1995). In nature, cycles of parthenogenetic reproduction are however alternated with phases of sexual reproduction where recombination of genetic information is happening. Production of resting eggs is therefore also regarded as a way to preserve the long-term fitness of genotypes in cyclical parthenogens (Serra and King, 1999).
In commercial mass cultures on the other hand, the rotifers are continuously driven to reproduce parthenogenetically, at high rates, in relatively extreme environmental conditions of high population density and high loads of organic matter (Lubzens et al., 2001). Moreover, the relative stability of culture conditions (salinity, temperature, feed type) in hatcheries is likely to result in extreme genetic selection in the rotifer population. Accidental or uncontrollable changes in environmental conditions might then very likely affect the long-term fitness of the population and finally result in crashes of the culture.