Intraspecific phylogeny of a Patagonian fescue: differentiation at molecular markers and morphological traits suggests hybridization at peripheral populations

Abstract

Background and aims: Grasses of the Festuca genus have complex phylogenetic relations due to morphological similarities among species and interspecific hybridization processes. Within Patagonian fescues, information concerning phylogenetic relationships is very scarce. In Festuca pallescens, a widely distributed species, the high phenotypic variability and the occurrence of interspecific hybridization preclude a clear identification of the populations. Given the relevance of natural rangelands for livestock production and their high degradation due to climate change, conservation actions are needed and knowledge about genetic variation is required.

Methods: To unravel the intraspecific phylogenetic relations and to detect genetic differences, we studied 21 populations of the species along its natural geographical distribution by coupling both molecular [internal transcribed spacer (ITS) and trnL-F markers] and morpho-anatomical analyses. Bayesian inference, maximum likelihood and maximum parsimony methods were applied to assemble a phylogenetic tree, including other native species. The morphological data set was analysed by discriminant and cluster analyses.

Key results: The combined information of the Bayesian tree (ITS marker), the geographical distribution of haplotype variants (trnL-F marker) and the morpho-anatomical traits, distinguished populations located at the margins of the distribution. Some of the variants detected were shared with other sympatric species of fescues.

Conclusions: These results suggest the occurrence of hybridization processes between species of the genus at peripheral sites characterized by suboptimal conditions, which might be key to the survival of these populations.

Keywords: Festuca; Festuca pallescens; ITS; Intraspecific genetic differentiation; Patagonia; chloroplast DNA markers; glacial refugia; hybridization; morpho-anatomical analyses; phylogenetic relationships; plant traits; speciation.

Fig. 1.

(A) Geographic distribution of the ITS variants of the evaluated populations of F. pallescens. Festuca pallescens variants are coloured in shades of green. (B) Bayesian tree based on nuclear ITS markers. Numbers above the branches indicate posterior probability values. The scale bar shows the expected substitutions per site. Pappostipa speciosa var. speciosa and Poa ligularis were used as outgroups.

Fig. 2.

Geographic distribution of the haplotypes detected in F. pallescens populations along the entire distribution range. Putative glacial refugia [lowland, peripheral and valley refugia as described by Sérsic et al. (2011)] for different plant species are delimited with blue lines. The box on the right shows the haplotype network. Haplotypes are represented with different-sized circles according to their frequencies (HyEc, hybrid ecotype; Fgra, F. gracillima; Fpur, F. purpurascens; Farg, F. argentina). Point mutations are shown as black lines and indels as red lines.

Fig. 3.

Scatterplot of scores derived from discriminant functions axis 1 and axis 2 produced by discriminant analysis applied to 30 morphological variables for the 12 populations of Festuca pallescens studied: ACA (solid squares), CLI (solid inverted triangles), PIL (solid diamonds), HUI (solid triangles), JAC (solid circles), CRO (open triangles), APE (open inverted triangles), GAI (open diamonds), LBA (open squares), RMA (open circles), FON (open pentagon), and BLE (open hourglasses).

Fig. 4.

Leaf cross-section of specimens stained with safranin showing examples of the different combinations of adaxial and/or abaxial girders of sclerenchyma of vascular bundles. Population names follow those of Supplementary Data Table S1. (A) Adaxial to abaxial girders of sclerenchyma in main vascular bundle. (B) Adaxial to abaxial girders of sclerenchyma in secondary vascular bundles. (C) Abaxial girders of sclerenchyma in main vascular bundle. (D) Abaxial girders of sclerenchyma in secondary vascular bundles. (E) Secondary vascular bundles without girders of sclerenchyma. (F) Main vascular bundle without girders of sclerenchyma.

Fig. 5.

Dendrogram resulting from cluster analysis obtained with the morphological data of F. pallescens populations. The dendrogram includes morpho-anatomical results of leaf cross-sections (following Fig. 4) and molecular variation according to ITS and cpDNA. The scale corresponds to Euclidean distance.