Cryptic invasion suggested by a cytogeographic analysis of the halophytic Puccinellia distans complex (Poaceae) in Central Europe.

Introduction: Despite the wealth of studies dealing with the invasions of alien plants, invasions of alien genotypes of native species (cryptic invasions) have been vastly neglected. The impact of cryptic invasions on the biodiversity of plant communities can, however, be significant. Inland saline habitats and halophytes (i.e., salt-tolerant plant species) are especially threatened by this phenomenon as they inhabit fragmented remnants of largely destroyed habitats, but at the same time some of these halophytic species are rapidly spreading along salt-treated roads. To study potential cryptic invasion of halophytes, the patterns of genome size and ploidy variation in the Puccinellia distans complex (Poaceae), the most rapidly spreading roadside halophyte in Central Europe, were investigated. Methods: DNA flow cytometry with confirmatory chromosome counts were employed to assess ploidy levels of 1414 individuals from 133 populations of the P. distans complex. In addition, climatic niche modelling was used to predict the distributions of selected cytotypes. Results: Eight groups differing in ploidy level and/or genome size were discovered, one diploid (2x; 2n = 14), two tetraploid (4xA, 4xB; 2n = 28), one pentaploid (5x; 2n = 35), three hexaploid (6xA, 6xB, 6xC; 2n = 42), and one heptaploid (7x; 2n = 49). The hexaploids (mostly the 6xC cytotype) were widespread through the study area, spreading intensively in both anthropogenic and natural habitats and probably hybridizing with the natural habitat dwelling tetraploids. In contrast, the non-hexaploid cytotypes rarely spread and were predominantly confined to natural habitats. Discussion: The extensive spread of the hexaploid cytotypes along roadsides has most likely facilitated their incursion into natural habitats. The colonization of new natural habitats by the hexaploids may pose a threat to the indigenous Puccinellia populations by compromising their genetic integrity and/or by outcompeting them.

Relative performance of customized and universal probe sets in target enrichment: A case study in subtribe Malinae.

PREMISE: Custom probe design for target enrichment in phylogenetics is tedious and often hinders broader phylogenetic synthesis. The universal angiosperm probe set Angiosperms353 may be the solution. Here, we test the relative performance of Angiosperms353 on the Rosaceae subtribe Malinae in comparison with custom probes that we specifically designed for this clade. We then address the impact of bioinformatically altering the performance of Angiosperms353 by replacing the original probe sequences with orthologs extracted from the Malus domestica genome. METHODS: To evaluate the relative performance of these probe sets, we compared the enrichment efficiency, locus recovery, alignment length, proportion of parsimony-informative sites, proportion of potential paralogs, the topology and support of the resulting species trees, and the gene tree discordance. RESULTS: Locus recovery was highest for our custom Malinae probe set, and replacing the original Angiosperms353 sequences with a Malus representative improved the locus recovery relative to Angiosperms353. The proportion of parsimony-informative sites was similar between all probe sets, while the gene tree discordance was lower in the case of the custom probes. DISCUSSION: A custom probe set benefits from data completeness and can be tailored toward the specificities of the project of choice; however, Angiosperms353 was equally as phylogenetically informative as the custom probes. We therefore recommend using both a custom probe set and Angiosperms353 to facilitate large-scale systematic studies, where financially possible.

The origin of unique diversity in deglaciated areas: traces of Pleistocene processes in north-European endemics from the Galium pusillum polyploid complex (Rubiaceae).

The role of glacial oscillations in shaping plant diversity has been only rarely addressed in endemics of formerly glaciated areas. The Galium pusillum group represents a rare example of an ecologically diverse and ploidy-variable species complex that exhibits substantial diversity in deglaciated northern Europe. Using AFLP and plastid and nuclear DNA sequences of 67 populations from northern, central, and western Europe with known ecological preferences, we elucidate the evolutionary history of lineages restricted to deglaciated areas and identify the eco-geographic partitioning of their genetic variation. We reveal three distinct endemic northern lineages: (i) diploids from southern Sweden + the British Isles, (ii) tetraploids from southern Scandinavia and the British Isles that show signs of ancient hybridization between the first lineage and populations from unglaciated central Europe, and (iii) tetraploids from Iceland + central Norway. Available evidence supports a stepwise differentiation of these three lineages that started at least before the last glacial maximum by processes of genome duplication, interlineage hybridization and/or allopatric evolution in distinct periglacial refugia. We reject the hypothesis of more recent postglacial speciation. Ecological characteristics of the populations under study only partly reflect genetic variation and suggest broad niches of postglacial colonizers. Despite their largely allopatric modern distributions, the north-European lineages of the G. pusillum group do not show signs of rapid postglacial divergence, in contrast to most other northern endemics. Our study suggests that plants inhabiting deglaciated areas outside the Arctic may exhibit very different evolutionary histories compared with their more thoroughly investigated high-arctic counterparts.