Our ability to predict adaptation trends is very limited in natural populations. Although we can efficiently predict adaptation to the selection of populations under highly controlled conditions, such as in breeding, researchers note a general lack of response to selection in wild populations. Despite the high diversity of natural populations and the existence of selection pressures, the response to selection does not appear to occur as expected.

This result may be explained by the fact that several mechanisms are acting at different levels of interaction (biotic, abiotic, etc ...), and that collectively may prevent the response to selection. Among the mechanisms identified are:

• Phenotypic plasticity
• Genetic correlations (correlation among genes that are thus selected jointly)
• Parental effects
• Fluctuating selection (the direction of selection of survivors vary with environmental conditions, which maintains diversity because selections can pull to different optimum at different times and places)

But two aspects still remain to be taken into account, the authors of the article say. First, these mechanisms are often acting simultaneously while we study them separately, thus ignoring the consequences of the accumulation and interactions. The second element is the existence of other mechanisms that still are not taken into account to date: non-genetic inheritance, co-evolution or demography.

In natural populations, as all mechanisms may be acting in different directions, it is not so surprising that selection is weaker than expected. This may drastically diminish the efficiency of each mechanism of selection in natural populations, thus allowing the maintenance of diversity, which can then be remobilized after the arousal of new environmental conditions.

« It is by integrating all these mechanisms at all levels that we will be able to correct our predictions of evolution, and that we will be able to explain why diversity is maintained. It is only at this cost that we will begin to get a more realistic picture of what happens in natural populations, and why they respond or do not respond to selection pressures. » concludes Benoit Pujol.