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

Saxifraga section Saxifraga subsection Arachnoideae is a lineage of 12 species distributed mainly in the European Alps. It is unusual in terms of ecological diversification by containing both high elevation species from exposed alpine habitats and low elevation species from shady habitats such as overhanging rocks and cave entrances. Our aims are to explore which of these habitat types is ancestral, and to identify the possible drivers of this remarkable ecological diversification. Using a Hybseq DNA-sequencing approach and a complete species sample we reconstructed and dated the phylogeny of subsection Arachnoideae. Using Landolt indicator values, this phylogenetic tree was used for the reconstruction of the evolution of temperature, light and soil pH requirements in this lineage. Diversification of subsection Arachnoideae started in the late Pliocene and continued through the Pleistocene. Both diversification among and within clades was largely allopatric, and species from shady habitats with low light requirements are distributed in well-known refugia. We hypothesize that low light requirements evolved when species persisting in cold-stage refugia were forced into marginal habitats by more competitive warm-stage vegetation. While we do not claim that such competition resulted in speciation, it very likely resulted in adaptive evolution.

How challenging RADseq data turned out to favor coalescent-based species tree inference. A case study in Aichryson (Crassulaceae).

Analysing multiple genomic regions while incorporating detection and qualification of discordance among regions has become standard for understanding phylogenetic relationships. In plants, which usually have comparatively large genomes, this is feasible by the combination of reduced-representation library (RRL) methods and high-throughput sequencing enabling the cost effective acquisition of genomic data for thousands of loci from hundreds of samples. One popular RRL method is RADseq. A major disadvantage of established RADseq approaches is the rather short fragment and sequencing range, leading to loci of little individual phylogenetic information. This issue hampers the application of coalescent-based species tree inference. The modified RADseq protocol presented here targets ca. 5,000 loci of 300-600nt length, sequenced with the latest short-read-sequencing (SRS) technology, has the potential to overcome this drawback. To illustrate the advantages of this approach we use the study group Aichryson Webb & Berthelott (Crassulaceae), a plant genus that diversified on the Canary Islands. The data analysis approach used here aims at a careful quality control of the long loci dataset. It involves an informed selection of thresholds for accurate clustering, a thorough exploration of locus properties, such as locus length, coverage and variability, to identify potential biased data and a comparative phylogenetic inference of filtered datasets, accompanied by an evaluation of resulting BS support, gene and site concordance factor values, to improve overall resolution of the resulting phylogenetic trees. The final dataset contains variable loci with an average length of 373nt and facilitates species tree estimation using a coalescent-based summary approach. Additional improvements brought by the approach are critically discussed.

Plastid genomes reveal recurrent formation of allopolyploid Fragaria.

PREMISE OF THE STUDY: Recurrent formation of polyploid taxa is a common observation in many plant groups. Haploid, cytoplasmic genomes like the plastid genome can be used to overcome the problem of homeologous genes and recombination in polyploid taxa. Fragaria (Rosaceae) contains several octo- and decaploid species. We use plastome sequences to infer the plastid ancestry of these taxa with special focus on the decaploid Fragaria cascadensis. METHODS: We used genome skimming of 96 polyploid Fragaria samples on a single Illumina HiSeq 3000 lane to obtain whole plastome sequences. These sequences were used for phylogenetic reconstructions and dating analyses. Ploidy of all samples was inferred with flow cytometry, and plastid inheritance was examined in a controlled cross of F. cascadensis. KEY RESULTS: The plastid genome phylogeny shows that only the octoploid F. chiloensis is monophyletic, all other polyploid taxa were supported to be para- or polyphyletic. The decaploid Fragaria cascadensis has biparental plastid inheritance and four different plastid donors. Diversification of the F. cascadensis clades occurred in the last 230,000 years. The southern part of its distribution range harbors considerably higher genetic diversity, suggestive of a potential refugium. CONCLUSIONS: Fragaria cascadensis had at least four independent origins from parents with different plastomes. In contrast, para- and polyphyletic taxa of the octoploid Fragaria species are best explained by incomplete lineage sorting and/or hybridization. Biogeographic patterns in F. cascadensis are probably a result of range shift during the last glacial maximum.

Two new species of Sabulina (Caryophyllaceae) from Washington State, U.S.A.

Sabulina basaltica and Sabulina sororia (Caryophyllaceae) are described as new species endemic to Washington State, U.S.A. Sabulina basaltica is restricted to high-elevation, basalt rocks in the northeastern Olympic Mountains, and Sabulina sororia to high-elevation, dunite rocks of the Twin Sisters Range in the North Cascade Mountains. Both were previously confused with Sabulina rossii (formerly called Arenaria rossii or Minuartia rossii). Their recognition as distinct species is supported by morphological and molecular characters and disjunct geographic distributions. Both are illustrated, mapped and compared to related species. We also present a molecular phylogeny of Sabulina based on nuclear ITS and plastid trnQ-rps16 DNA with increased sampling of North American taxa. The phylogeny resolves a single clade containing all glabrous, perennial, North American Sabulina taxa including Sabulina rossii and both of the new species.

Simultaneous speciation in the European high mountain flowering plant genus Facchinia (Minuartia s.l., Caryophyllaceae) revealed by genotyping-by-sequencing.

Understanding the relative importance of different mechanisms of speciation in a given lineage requires fully resolved interspecific relationships. Using Facchinia, a genus of seven species centred in the European Alps, we explore whether the polytomy found by Sanger sequencing analyses of standard nuclear (ITS) and plastid markers (trnQ-rps16) is a hard or soft polytomy by substantially increasing the amount of DNA sequence data, generated by genotyping-by-sequencing. In comparison to 142 phylogenetically informative sites in the Sanger sequences the GBS sequences yielded 3363 phylogenetically informative sites after exclusion of apparently oversaturated SNPs. Maximum parsimony, maximum likelihood, NeighborNet, SVDquartets and Astral-II analyses all resulted in phylogenetic trees (and networks) in which interspecific relationships were largely unresolved. After excluding incomplete lineage sorting, hybridisation and oversaturation of characters as possible causes for lack of phylogenetic resolution, we conclude that the polytomy obtained most likely represents a hard polytomy. We hypothesize that diversification of Facchinia is best interpreted as the result of multiple simultaneous vicariance in response to climatic changes during the Early Quaternary.

The phylogeny of the European high mountain genus Adenostyles (Asteraceae-Senecioneae) reveals that edaphic shifts coincide with dispersal events.

PREMISE OF THE STUDY: Heterogeneity of edaphic conditions plays a large role in driving the diversification of many plant groups. In the Alps and other European high mountains, many closely related calcicole and calcifuge plant taxa exist. To better understand patterns and processes of edaphic differentiation, the phylogeny of the edaphically variable genus Adenostyles was studied. The genus contains three species, of which A. alpina has five subspecies. Each species and subspecies is largely confined to either calcareous or noncalcareous substrates. • METHODS: We analyzed the phylogeny of Adenostyles using DNA sequences of nrITS, nrETS, nuclear chalcone synthase, and three plastid markers (rpl32-trnL, psbA-trnH, and ndhF-rpl32) from 45 in-group and five out-group samples. The phylogeny was used to reconstruct ancestral edaphic associations and distribution areas. • KEY RESULTS: Within Adenostyles alpina, the shifts of edaphic association from calcicole to calcifuge in subsp. briquetii (Corsica) and in a clade of subsp. macrocephala (southernmost Italy) plus subsp. pyrenaica (Pyrenees) coincide with dispersal events. • CONCLUSIONS: We conclude that colonization of areas with novel edaphic conditions via dispersal can trigger shifts of edaphic association. Accordingly, edaphic niche shifts can result from chance events.