DEVELOPMENTAL NOISE, PHENOTYPIC PLASTICITY, AND ALLOZYME HETEROZYGOSITY IN DAPHNIA

Previous theories and studies have postulated negative correlations be tween allozyme heterozygosity and developmental noise and between hete rozygosity and phenotypic plasticity. We examined these relationships for morphological and life-history traits of Daphnia magna in four ind ependent experiments using two different Moscow populations and one Ge rman population. Clones were raised under a range of food levels or in dividual densities. Heterozygosity was scored at five allozyme loci in two experiments and at three loci in two others. Relative differences in developmental noise among clones with different heterozygosity lev els were estimated as the pooled residual variation from an analysis o f variation that removed the effects of macroenvironment, clones, and their interaction. Plasticity was measured as the amount of macroenvir onmental variation plus genotype-by-environment interaction variation. We found a positive correlation between developmental noise and heter ozygosity, although this correlation varied among traits and experimen ts. This result contradicts most previous claims about these relations hips. In contrast, we found that phenotypic plasticity and heterozygos ity were negatively correlated for some traits. Developmental noise an d phenotypic plasticity were correlated for only two traits in two dif ferent experiments. This trait-specific relationship is in concordance with previous studies. Our results could not be explained by effects of developmental time, a previously hypothesized mechanism. We propose several explanations for our results and the disparate results of oth ers that do not require that heterozygosity be the actual cause of var iation in developmental noise.