Multidimensional divergent selection, local adaptation, and speciation

Abstract

Divergent selection applied to one or more traits drives local adaptation and may lead to ecological speciation. Divergent selection on many traits might be termed “multidimensional” divergent selection. There is a commonly held view that multidimensional divergent selection is likely to promote local adaptation and speciation to a greater extent than unidimensional divergent selection. We disentangle the core concepts underlying dimensionality as a property of the environment, phenotypes, and genome. In particular, we identify a need to separate the overall strength of selection and the number of loci affected from dimensionality per se, and to distinguish divergence dimensionality from dimensionality of stabilizing selection. We then critically scrutinize this commonly held view that multidimensional selection promotes speciation, re‐examining the evidence base from theory, experiments, and nature. We conclude that the evidence base is currently weak and generally suffers from confounding of possible causal effects. Finally, we propose several mechanisms by which multidimensional divergent selection and related processes might influence divergence, both as a driver and as a barrier.

Faster-haplodiploid evolution under divergence-with-gene-flow: simulations and empirical data from pine-feeding hymenopterans

“…Consistent with a "multifarous" or "multidimensional" model of divergent selection (Feder & Nosil, 2010;Rice & Hostert, 1993;White & Butlin, 2021), multiple unlinked loci exceeded expected levels of differentiation under neutrality (Figure 7). We also observed multiple regions of unusually low differentiation, which could be explained by adaptive introgression.…”

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

“…Reproductive isolation appears stronger when it involves multiple barriers linked to multiple traits and multiple ecological axes than in cases of unidimensional divergence [3][4][5] . The matter of dimensionality also arises at the intra-specific level when studying local adaptation 6,7 . Environments can differ in one aspect (for example, temperature, salinity, or humidity) or multiple aspects, and fitness may involve one trait (such as colour, growth rate, or size) or multiple traits.…”

Signatures of natural selection in a foundation tree along Mediterranean climatic gradients

“…The patterns of genomic turnover associated with the studied climatic variables are aligned with the climatic gradients of the region (Figure 4 ). These associations are indicative of the multidimensional patterns of adaptation resulting in uncorrelated intraspecific selection among SNPs (White & Butlin, 2021 ). Here, we define dimensionality as the interaction between uncorrelated climate variables to independently describe each habitat.…”