Survival in nunatak and peripheral glacial refugia of three alpine plant species is partly predicted by altitudinal segregation.

Mountain biota survived the Quaternary cold stages most probably in peripheral refugia and/or ice-free peaks within ice-sheets (nunataks). While survival in peripheral refugia has been broadly demonstrated, evidence for nunatak refugia is still scarce. We generated RADseq data from three mountain plant species occurring at different elevations in the southeastern European Alps to investigate the role of different glacial refugia during the Last Glacial Maximum (LGM). We tested the following hypotheses. (i) The deep Piave Valley forms the deepest genetic split in the species distributed across it, delimiting two peripheral refugia. (ii) The montane to alpine species Campanula morettiana and Primula tyrolensis survived the LGM in peripheral refugia, while high-alpine to subnival Saxifraga facchinii likely survived in several nunatak refugia. (iii) The lower elevation species suffered a strong population decline during the LGM. By contrast, the higher elevation species shows long-term stability of population sizes due to survival on permanently ice-free peaks and small population sizes at present. We found peripheral refugia on both sides of the Piave Valley, which acted as a major genetic barrier. Demographic modelling confirmed nunatak survival not only for S. facchinii but also for montane to alpine C. morettiana. Altitudinal segregation influenced the species' demographic fluctuations, with the lower elevation species showing a significant population increase at the end of the LGM, and the higher elevation species either showing decrease towards the present or stable population sizes with a short bottleneck. Our results highlight the role of nunatak survival and species ecology in the demographic history of mountain species.

Homoploid hybrids are common but evolutionary dead ends, whereas polyploidy is not linked to hybridization in a group of Pyrenean saxifrages.

Hybridization and polyploidy are major forces in plant evolution. Homoploid hybridization can generate new species via hybrid speciation, or modify extant evolutionary lineages through introgression. Polyploidy enables instantaneous reproductive isolation from the parental lineage(s) and is often coupled with evolutionary innovations, especially when linked to hybridization. While allopolyploidy is a well-known and common mechanism of plant speciation, the evolutionary role of autopolyploidy might have been underestimated. Here, we studied the saxifrages of Saxifraga subsection Saxifraga in the Pyrenees, which easily hybridise and include polyploid populations of uncertain origin, as a model to unravel evolutionary consequences and origin of hybridization and polyploidy. Additionally, we investigate the phylogenetic relationship between the two subspecies of the endemic S. pubescens to ascertain whether they should rather be treated as different species. For these purposes, we combined ploidy-informed restriction associated DNA analyses, plastid DNA sequences and morphological data on a comprehensive population sample of seven species. Our results unravel multiple homoploid hybridization events at the diploid level between different species pairs, but with limited evolutionary impact. The ploidy-informed analyses reveal that all tetraploid populations detected in the present study belong to the widespread alpine species S. moschata. Although of autopolyploid origin, they are to some extent morphologically differentiated and underwent a different evolutionary pathway than their diploid parent. However, the high plastid DNA diversity and the internal structure within eastern and western population groups suggest multiple origins of the polyploids. Finally, our phylogenetic analyses show that S. pubescens and S. iratiana are clearly not sister lineages, and should consequently be considered as independent species.

Macroevolutionary dynamics of nectar spurs, a key evolutionary innovation.

Floral nectar spurs are widely considered a key innovation promoting diversification in angiosperms by means of pollinator shifts. We investigated the macroevolutionary dynamics of nectar spurs in the tribe Antirrhineae (Plantaginaceae), which contains 29 genera and 300-400 species (70-80% spurred). The effect of nectar spurs on diversification was tested, with special focus on Linaria, the genus with the highest number of species. We generated the most comprehensive phylogeny of Antirrhineae to date and reconstructed the evolution of nectar spurs. Diversification rate heterogeneity was investigated using trait-dependent and trait-independent methods, and accounting for taxonomic uncertainty. The association between changes in spur length and speciation was examined within Linaria using model testing and ancestral state reconstructions. We inferred four independent acquisitions of nectar spurs. Diversification analyses revealed that nectar spurs are loosely associated with increased diversification rates. Detected rate shifts were delayed by 5-15 Myr with respect to the acquisition of the trait. Active evolution of spur length, fitting a speciational model, was inferred in Linaria, which is consistent with a scenario of pollinator shifts driving diversification. Nectar spurs played a role in diversification of the Antirrhineae, but diversification dynamics can only be fully explained by the complex interaction of multiple biotic and abiotic factors.

Postglacial range expansion of high-elevation plants is restricted by dispersal ability and habitat specialization.

Aim: Species' ecological traits influence their spatial genetic patterns. Bedrock preference strongly shapes the phylogeography of alpine plants, but its interactions with other ecological traits have rarely been disentangled. Here, we explore whether dispersal ability and degree of habitat specialization account for divergent postglacial expansion patterns of high-elevation plants in spite of similar bedrock preference. Location: The Pyrenees, southwestern Europe. Taxon: Cirsium glabrum (Asteraceae), Salix pyrenaica (Salicaceae) and Silene borderei (Caryophyllaceae). Methods: Phylogenetic, genetic structure and demographic modelling analyses based on restriction-site-associated DNA sequencing (RADseq) data from a range-wide populational sampling were conducted. Occurrence data and environmental variables were used to construct species distribution models, which were projected under current and Last Glacial Maximum conditions, and were combined with RADseq data to reconstruct the postglacial history of the study species. The degree of habitat specialization of each species was estimated based on the plant communities within which they occur, and their climatic niche breadth. Results: Salix pyrenaica, which occupies a broad range of habitats, shows a high level of range filling, a blurred genetic structure and an admixture cline between the two main genetic groups, congruent with rapid postglacial expansion. The microsite specialists C. glabrum and S. borderei exhibit a strong genetic structure and low levels of range filling, indicative of slow postglacial expansion. The good disperser C. glabrum shows higher levels of admixture between genetic groups and weaker population differentiation than the poor disperser S. borderei. Main Conclusions: Factors other than bedrock preference have a strong impact on the postglacial range dynamics of high-elevation species. Habitat specialization plays an important role, allowing species occupying a broad range of habitats to more rapidly expand their ranges after environmental change. The effect of dispersal ability is lower than expected for the study species.

Phylogeography of western Mediterranean Cymbalaria (Plantaginaceae) reveals two independent long-distance dispersals and entails new taxonomic circumscriptions.

The Balearic Islands, Corsica and Sardinia (BCS) constitute biodiversity hotspots in the western Mediterranean Basin. Oligocene connections and long distance dispersal events have been suggested to cause presence of BCS shared endemic species. One of them is Cymbalaria aequitriloba, which, together with three additional species, constitute a polyploid clade endemic to BCS. Combining amplified fragment length polymorphism (AFLP) fingerprinting, plastid DNA sequences and morphometrics, we inferred the phylogeography of the group and evaluated the species' current taxonomic circumscriptions. Based on morphometric and AFLP data we propose a new circumscription for C. fragilis to additionally comprise a group of populations with intermediate morphological characters previously included in C. aequitriloba. Consequently, we suggest to change the IUCN category of C. fragilis from critically endangered (CR) to near threatened (NT). Both morphology and AFLP data support the current taxonomy of the single island endemics C. hepaticifolia and C. muelleri. The four species had a common origin in Corsica-Sardinia, and two long-distance dispersal events to the Balearic Islands were inferred. Finally, plastid DNA data suggest that interspecific gene flow took place where two species co-occur.