Phylogeny of Saxifraga section Saxifraga subsection Arachnoideae (Saxifragaceae) and the origin of low elevation shade-dwelling species

Hybrid zones in the European Alps impact the phylogeography of alpine vicariant willow species (Salix L.)

Introduction

In the European Alps, Pleistocene climate oscillations resulted in geographical range expansions and restrictions of species. Postglacial recolonizations often result in secondary contact hybridization of vicariant species, thereby creating hybrid zones with patterns of introgression. Here, we compare the genetic structure of two secondary contact hybrid zones between two vicariant willow species pairs occurring in the European Alpine System. Supplemented by morphological and ecological data, we try to understand the factors shaping the hybrid zones and their influence on geographical range filling patterns.

Methods

RAD sequencing and morphometric data were used to characterize biogeographical history, genetic diversity and the hybrid zone of each species pair. Vegetation relevés and species distribution models provided ecological context and support.

Key results

Results suggest that recolonization of the Alps happened from peripheral glacial refugia, resulting in broad secondary contact zones in the Eastern Alps in both species pairs. Both hybrid zones show introgression, but differ in symmetry and intensity of gene flow, in the type of introgressed loci, and in the geographical range. Habitat preferences and species distribution models do not indicate ecological barriers to recolonization.

Conclusions

Hybrid zones do not only affect the genetic structure of species by gene flow and introgression, but also appear to impact the biogeographical patterns of species.

Climatic and edaphic niche shifts during plant radiation in the Mediterranean biodiversity hotspot

BACKGROUND AND AIMS

Ecological speciation is frequently invoked as a driver of plant radiation, but the behaviour of environmental niches during radiation is contentious, with patterns ranging from niche conservatism to niche divergence. Here, we investigated climatic and edaphic niche shifts during radiation in a western Mediterranean lineage of the genus Linaria (Plantaginaceae).

METHODS

Detailed distributional, phylogenomic and environmental data were integrated to analyse changes in climatic and edaphic niches in a spatiotemporal context, including calculation of niche overlap, niche equivalency and similarity tests, maximum entropy modelling, phylogenetic comparative methods and biogeographical analyses.

KEY RESULTS

Active divergence of climatic and edaphic niches within a limited subset of available conditions was detected among the eight study species and particularly between sister species. Speciation and niche divergence are estimated to have happened in the southern Iberian Peninsula in Mediterranean conditions, followed by waxing and waning of distribution ranges resulting from the Quaternary climatic cycles.

CONCLUSIONS

The results support the idea that the prevalence of niche conservatism or niche divergence patterns is a matter of phylogenetic scale. Habitat isolation pertaining to both climatic and soil conditions appears to have played a role in plant speciation in the western Mediterranean biodiversity hotspot, most probably in combination with pollinator isolation and some degree of geographical isolation. These findings are in agreement with an adaptive radiation scenario incorporating certain non-adaptive features.

Corrigendum

[This corrects the article DOI: 10.1002/ece3.9728.].