Potential adaptive divergence between subspecies and populations of snapdragon plants inferred fromQST-FSTcomparisons

Phenotypic divergence among natural populations can be explained by natural selection or by neutral processes such as drift. Many examples in the literature compare putatively neutral (F-ST) and quantitative genetic (Q(ST)) differentiation in multiple populations to assess their evolutionary signature and identify candidate traits involved with local adaptation. Investigating these signatures in closely related or recently diversified species has the potential to shed light on the divergence processes acting at the interspecific level. Here, we conducted this comparison in two subspecies of snapdragon plants (eight populations ofAntirrhinum majus pseudomajusand five populations ofA. m. striatum) in a common garden experiment. We also tested whether altitude was involved with population phenotypic divergence. Our results identified candidate phenological and morphological traits involved with local adaptation. Most of these traits were identified in one subspecies but not the other. Phenotypic divergence increased with altitude for a few biomass-related traits, but only inA. m. striatum. These traits therefore potentially reflectA. m. striatumadaptation to altitude. Our findings imply that adaptive processes potentially differ at the scale ofA. majussubspecies.