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

Abstract

IntroductionDespite 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.MethodsDNA 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.ResultsEight 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.DiscussionThe 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.

Hybrids as mirrors of the past: genomic footprints reveal spatio-temporal dynamics and extinction risk of alpine extremophytes in the mountains of Central Asia

“…The studied group is a mixed-ploidy system, in which alkali grasses are represented primarily by diploids and tetraploids ( Sokolovskaya and Probatova, 1975 ; Tzvelev, 1976 ; Guinochet and Lefranc, 1981 ; Zakharyeva, 1985 ; Yan et al., 1989 ; Zakharjeva, 1993 ; Probatova et al., 2013 ; Kumar et al., 2018 ). However, higher ploidies were also reported for P. hackeliana and P. distans agg ( Hughes, 1976 ; Tzvelev, 1976 ; Hughes and Halliday, 1980 ; Davis and Consaul, 2007 ; Kúr et al., 2023 ). The full list of ploidy levels reported for each taxon is shown in Supplementary Table 1 .…”

“…Alkali grasses are known for their wide array of ploidy levels ( Kúr et al., 2023 ). However, alpine species are represented primarily by diploids and tetraploids according to a few available chromosome counts ( Supplementary Table 1 ).…”

“…Despite problematic identification and unknown phylogeny, to date, no large-scale study has examined the relationships among alpine Puccinellia and permeability of species boundaries. Hybridization may be an essential driver of speciation among high mountain Puccinellia given the frequent gene flow events detected among their lowland relatives ( Steen et al., 2004 ; Davis and Consaul, 2007 ; Consaul et al., 2010 ; Gnutikov et al., 2020 ; Soreng et al., 2022 ; Kúr et al., 2023 ). In this study, we combine morphology and genomic data to investigate evolutionary patterns among alpine alkali grasses in the Pamir Mountains, the diversity center of the genus in the Mountains of Central Asia ( Ovchinnikov and Chukavina, 1957 ; Dickoré, 1995 ; Liang et al., 2006 ; Lazkov and Sultanova, 2014 ).…”

“…Taxonomic diversity and evolutionary complexity in a widely distributed P. distans agg. are a separate research challenge ( Davis and Consaul, 2007 ; Kúr et al., 2023 ), remaining beyond the main focus of this study. Here, we put special emphasis on unraveling the origins of P. vachanica , a taxon with a poorly recognized distribution range and unclear status, which was described from the lower Wakhan Corridor in the southern edges of the Pamir Mountains ( Ovchinnikov and Chukavina, 1957 ).…”