Résumé
Background Anthropogenic disturbances can lead to intense selection
pressures on traits and very rapid evolutionary changes. Evolutionary
responses to environmental changes, in turn, reflect changes in the
genetic structure of the traits, accompanied by a reduction of
evolutionary potential of the populations under selection. Assessing the
effects of pollutants on the evolutionary responses and on the genetic
structure of populations is thus important to understanding the mechanisms
that entail specialization to novel environmental conditions or resistance
to novel stressors. Results Using an experimental evolution approach we
exposed Caenorhabditis elegans populations to uranium, salt and
alternating uranium-salt environments over 22 generations. We analyzed the
changes in the average values of life history traits and the consequences
at the demographic level in these populations. We also estimated the
phenotypic and genetic (co)variance structure of these traits at different
generations. Compared to populations in salt, populations in uranium
showed a reduction of the stability of their traits structure and a higher
capacity to respond by acclimation. However, the evolutionary responses of
traits were generally lower for uranium than salt and the evolutionary
responses in the alternating uranium-salt environment were between those
of constant environments. Consequently, at the end of the experiment, the
population rate of increase were higher in uranium than in salt and
intermediate in the alternating environment. Conclusions Our
multigenerational experiment confirmed that rapid adaptation to different
polluted environments may involve different evolutionary responses
resulting demographic consequences. These changes are partly explain by
the effects of the pollutants on the genetic (co)variance structure of
traits and the capacity of acclimation to novel conditions. Finally, our
results in the alternating environment may confirm the selection of a
generalist type in this environment.