Experimental evolution of local adaptation under unidimensional and multidimensional selection

Evolution: How important is the dimensionality of natural selection in local adaptation?

“…On the other hand, spreading selection across multiple traits and loci may lead to a weaker effect on fitness and adaptation may be slowed down by gene flow and recombination for unlinked loci 3,6 . The results presented by White et al 8 partially validate and contradict both predictions. In their study, both unidimensional and multidimensional divergent selection led to local adaptation, but they differed in magnitude over time.…”

“…This result agrees with a meta-analysis suggesting that adaptation is stronger when dimensionality is higher 7 . However, over the course of the experiment, local adaptation between multidimensional environments declined 8 . In contrast, unidimensional divergence ultimately led to stronger local adaptation than multidimensional divergence, but occurred more slowly 8 Overall, the dynamic of adaptation appears as a crucial parameter that is affected by the dimensionality of environmental divergence.…”

“…To investigate the effects of environmental dimensionality on local adaptation, White and collaborators 8 designed an ambitious experimental-evolution set up using a species of monogonont rotifer, Brachionus plicatilis, a type of small aquatic invertebrate. Population pairs of B. plicatilis were split between environments differing by either one or three stressors (Figure 1).…”

“…To fully understand what shapes the dynamics of adaptation, it is worth returning to the initial definition. In White et al 8 , local adaptation was defined following the classic measure of 'home versus away' fitness 9 -that is, the difference between fitness in the local conditions and fitness in the contrasting conditions for each experimental pair of environments. However, examining changes in fitness separately reveals a more complex pattern.…”

“…Because reproductive isolation is an additional step that may, or may not, follow local adaptation, the impact of selection dimensionality on those evolutionary processes can differ 2,6 . For instance, although multidimensional divergence may favour the completion of speciation between highly divergent populations 3 , it may rather impede early stages of local adaptation through the evolution of generalist populations 8 . Altogether, the question of how dimensionality in divergent selection impacts evolutionary dynamics thus appears non-trivial, and new studies like the one by White et al 8 will inspire complementary theoretical and empirical work to better refine predictions.…”