Assortative mating and gene flow generate clinal phenological variation in trees.

Jean-Paul Soularue,Antoine Kremer

doi:10.1186/1471-2148-12-79

Abstract

BackgroundOn-going climate change is shifting the timing of bud burst (TBB) of broad leaf and conifer trees in temperate areas, raising concerns about the abilities of natural populations to respond to these shifts. The level of expected evolutionary change depends on the level and distribution of genetic variation of TBB. While numerous experimental studies have highlighted the role of divergent selection in promoting clinal TBB differentiation, we explored whether the observed patterns of variation could be generated by the joint effects of assortative mating for TBB and gene flow among natural populations. We tested this hypothesis using an in silico approach based on quantitative genetic models.ResultsOur simulations showed that genetic clines can develop even without divergent selection. Assortative mating in association with environmental gradients substantially shifted the mean genetic values of populations. Owing to assortative mating, immigrant alleles were screened for proximal or distant populations depending on the strength of the environmental cline. Furthermore, we confirmed that assortative mating increases the additive genetic variance within populations. However, we observed also a rapid decline of the additive genetic variance caused by restricted gene flow between neighboring populations resulting from preferential matings between phenologically-matching phenotypes.ConclusionsWe provided evidence that the patterns of genetic variation of phenological traits observed in forest trees can be generated solely by the effects of assortative mating and gene flow. We anticipate that predicted temperature increases due to climate change will further enhance genetic differentiation across the landscape. These trends are likely to be reinforced or counteracted by natural selection if phenological traits are correlated to fitness.

Highlights

IntroductionIntroduction to Forest GeneticsNew-York: Academic Press, INC.; 1976.47. Morgenstern EK: Geographic variation in Forest TreesGenetic Basis and Application of Knowledge in Silviculture
Introduction to Forest GeneticsNew-York: Academic Press, INC.; 1976.47
Monitoring of leaf unfolding in various species across their distributions has shown that global warming will trigger earlier flushing [2,3,4]. These observations have raised concerns about the capacity of tree populations to cope with changes in the timing of bud burst (TBB), which is related to the fitness of trees in two ways: (i) it establishes the length of the growing season and is a major determinant of growth [5], (ii) it determines the timing of flowering, so is related to fecundity [6]

Summary

Introduction

Introduction to Forest GeneticsNew-York: Academic Press, INC.; 1976.47. Morgenstern EK: Geographic variation in Forest TreesGenetic Basis and Application of Knowledge in Silviculture. While numerous experimental studies have highlighted the role of divergent selection in promoting clinal TBB differentiation, we explored whether the observed patterns of variation could be generated by the joint effects of assortative mating for TBB and gene flow among natural populations. Monitoring of leaf unfolding in various species across their distributions has shown that global warming will trigger earlier flushing [2,3,4] These observations have raised concerns about the capacity of tree populations to cope with changes in the timing of bud burst (TBB), which is related to the fitness of trees in two ways: (i) it establishes the length of the growing season and is a major determinant of growth [5], (ii) it determines the timing of flowering, so is related to fecundity [6]. In the case of beech, genetic clines are opposite to phenotypic clines and exhibit counter-gradient variation: provenances from northern latitudes flush earlier than populations from southern latitudes [18,19]

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