Individual variability is the key for tolerating environmental change

When animal (or plant) populations must face environmental change such as increased themperature, eutrophication etc. the greater the variability between organisms, the more likely it is that at least some specimens are able to tolerate the disturbed conditions. Hitherto it has been virtually always been thoght that the only important thing in this regard is genetic variability. However, individual variation is possible also without genetic variation: a single genotype can have quite different phenotypes, which tolerate different conditions. 

In the case that the environment is very labile such phenotypic plasticity - i.e. individual variations in physiological function of one genotype - is better way of tolerating unfavourable environment than having genetically heterogenous populatio with one genotype tolerating that environmental problem. This is because the plasticity of the individuals that tolerate the unfavourable environment is as large as that of the original population. If, however, the tolerance depends on the genotypic variation, it is likely that the overall plasticity of the tolerant genotype is smaller than that of the original, genetically variable population. Genetical variability can be of significant benefit only in cases where the change is to one direction. The possible importance of measures of individual variation in environmental response has recently been discussed in our article (Nikinmaa and Anttila, Aquatic Toxicology, 207, 29-33; open access). Our experimental results on oil-exposed water fleas also indicate that a change in individual variability can occur even when no change is seen in the mean of the measured parameter.