Despite admixing two closely related Carex species differ in their regional morphological differentiation

Lisanna Schmidt,Bernhard Schmid,Tatjana Oja,Markus Fischer

doi:10.1007/s00606-017-1420-0

Abstract

Rarer species are expected to show stronger geographic differentiation than more common species. However, if rare species hybridize with common species, differentiation may be quite similar between the two due to genetic admixing via backcrossing. We studied morphological differentiation of plants of 21 natural populations of the more common Carex flava, 16 of the less common Carex viridula and 6 of their hybrids from 27 sites in three climatically different regions, Estonia, Lowland Switzerland and Highland Switzerland. Univariate ANOVA and multivariate principal component analysis of 14 morphological characters, describing both vegetative and reproductive characters, allowed to clearly distinguish C. flava from C. viridula. Carex viridula populations showed stronger regional variation than C. flava. Hybrids had both intermediate and transgressive characters in Switzerland and Estonia. On average, hybrids from Lowland Switzerland were more similar to Swiss C. flava than to C. viridula, while hybrids from Estonia were morphologically intermediate between plants of Estonian populations of the parental species. The results suggest that within-region genetic admixing between species has limited potential to lead to region-specific similarity between species, at least in our model system of the C. flava complex. We conclude that C. flava and C. viridula are clearly distinct species and that, despite hybridization, geographic differentiation is more pronounced in the less common C. viridula than in C. flava.

Highlights

Widespread plant species often display remarkable morphological variation across their area of distribution, which often spans considerable environmental gradients
Hybrids from Lowland Switzerland were more similar to Swiss C. flava than to C. viridula, while hybrids from Estonia were morphologically intermediate between plants of Estonian populations of the parental species
In Highland Switzerland, the interspecific differentiation was evident only in the generally more constant female spike and utricle characters (Figs. 1, 2). This is because C. flava forms dwarf phenotypes at higher altitudes, sometimes referred to as C. flava var. alpina Kneucker (Schmid 1983), which are more similar to C. viridula

Summary

Introduction

Widespread plant species often display remarkable morphological variation across their area of distribution, which often spans considerable environmental gradients. Among possible causes are phenotypic plasticity or variation due to local adaptation (West-Eberhard 2003). Plant phenotypic variation and performance have been found to change with latitude (Santamaría et al 2003; Hall et al 2007) and altitude (Clausen et al 1948; Jonas and Geber 1999). Patterns of phenotypic variation in higher plants are influenced by hybridization and introgression between taxa (Anderson 1949; Arnold 2006). Hybridization and introgression can lead to genetic admixing (Lexer et al 2010; Rius and Darling 2014; Hahn and Rieseberg 2016) between closely related and co-occurring species, reducing phenotypic differences

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