Potential adaptive divergence between subspecies and populations of snapdragon plants inferred from QST -FST comparisons.

Sara Marin,Anaïs Gibert,Mylène Lascoste,Juliette Archambeau,Vincent Bonhomme,Benoit Pujol

doi:10.1111/mec.15546

Abstract

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 of Antirrhinum majus pseudomajus and five populations of A. 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 in A. m. striatum. These traits therefore potentially reflect A. m. striatum adaptation to altitude. Our findings imply that adaptive processes potentially differ at the scale of A. majus subspecies.

Highlights

Local adaptation - the evolutionary response to selection that makes populations fitter in their own local habitat than in other populations' local habitats - is widespread in both plant and animal species (Halbritter et al, 2018; Kawecki & Ebert, 2004; Leinonen, McCairns, O'Hara, & Merilä, 2013)
We investigate patterns of local adaptation in two closely related plant subspecies of Snapdragon (Antirrhinum majus L., Plantaginaceae) by using QST–FST comparisons estimated in a common garden experiment, and evaluate whether altitudinal gradients might play a role in the potential adaptive divergence of populations
We tested whether traits were potentially involved with local adaptation by comparing QST and FST, and we investigated whether quantitative genetic differentiation increased with altitudinal difference, and the possibility that environmental changes associated with altitude, which include a suite of climatic variables, drove adaptive responses

Summary

| INTRODUCTION

Local adaptation - the evolutionary response to selection that makes populations fitter in their own local habitat than in other populations' local habitats - is widespread in both plant and animal species (Halbritter et al, 2018; Kawecki & Ebert, 2004; Leinonen, McCairns, O'Hara, & Merilä, 2013). Halbritter et al (2018) combined the information from studies of multiple plant species along elevation gradients They found significant evidence for adaptation to different elevations in terms of survival and biomass, with a lower survival at foreign elevations, and a clear trend towards smaller plants at higher elevation. We investigate patterns of local adaptation in two closely related plant subspecies of Snapdragon (Antirrhinum majus L., Plantaginaceae) by using QST–FST comparisons estimated in a common garden experiment, and evaluate whether altitudinal gradients might play a role in the potential adaptive divergence of populations. Pseudomajus, and come frequently into contact at the margins of their ranges where there is evidence for gene exchange (Khimoun et al, 2011; Ringbauer, Kolesnikov, Field, & Barton, 2018) Their geographic separation is not explained by actual climatic differences, as illustrated by the substantial overlap of environmental conditions between the two subspecies (Khimoun et al, 2013). We tested whether traits were potentially involved with local adaptation by comparing QST and FST, and we investigated whether quantitative genetic differentiation increased with altitudinal difference, and the possibility that environmental changes associated with altitude, which include a suite of climatic variables, drove adaptive responses

| MATERIALS AND METHODS

| DISCUSSION

Findings

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