Genome Size in the Arenaria ciliata Species Complex (Caryophyllaceae), with Special Focus on A. ciliata subsp. bernensis, a Narrow Endemic of the Swiss Northern Alps

Abstract

The genus Arenaria (Caryophyllaceae) comprises approximately 300 species worldwide; however, to date, just six of these taxa have been investigated in terms of their genome size. The main subject of the present study is the A. ciliata species complex, with special focus on A. ciliata subsp. bernensis, an endemic plant occurring in the Swiss Northern Alps. Altogether, 16 populations and 77 individuals of the A. ciliata complex have been sampled and their genome sizes were estimated using flow cytometry, including A. ciliata subsp. bernensis, A. ciliata s.str., A. multicaulis, and A. gothica. The Arenaria ciliata subsp. bernensis shows the highest 2c-value of 6.91 pg of DNA, while A. gothica showed 2c = 3.69 pg, A. ciliata s.str. 2c = 1.71 pg, and A. multicaulis 2c = 1.57 pg. These results confirm the very high ploidy level of A. ciliata subsp. bernensis (2n = 20x = 200) compared to other taxa in the complex, as detected by our chromosome counting and previously documented by earlier work. The genome size and, thus, also the ploidy level, is stable across the whole distribution area of this taxon. The present study delivers additional support for the taxonomic distinctiveness of the high alpine endemic A. ciliata subsp. bernensis, which strongly aligns with other differences in morphology, phylogeny, phenology, ecology, and plant communities, described previously. In affirming these differences, further support now exists to re-consider the species status of this taxon. Upgrading to full species rank would significantly improve the conservation prospects for this taxon, as, because of its precise ecological adaptation to alpine summit habitats, the A. ciliata subsp. bernensis faces acute threats from accelerated climate warming.

Keywords: arctic-alpine plants; disjunctions; flow cytometry; narrow endemism; polyploidy.

Figure 1

Habitats and morphology of Arenaria ciliata subsp. bernensis. (A)—Summit area of Gantrisch (2175 m a.s.l., Canton of Bern), view from Leiterenpass, the locus classicus of the taxon. (B)—Typical habitat on shady and cold slopes with northern exposition at the elevations higher than 2000 m a.s.l. (ca. 2100 m a.s.l., Schafarnisch, Canton of Fribourg). (C)—Only few small populations or isolated individuals grow at lower altitudes, at the bases of scree fields with north exposition (Salzmatt next to Kaiseregg, 1650 m a.s.l.). (D)—Example of irregular floral morphology of plants with 6 to 9 petals (typical number is 5) (Leiterenpass, 1940 m a.s.l.). Pictures: G. Kozlowski.

Figure 2

Distribution area of Arenaria ciliata subsp. bernensis (yellow zones). Orange circles show the position of collection sites with the numbers of individuals sampled in the given summit area.

Figure 3

Variation in genome size of four taxa in the Arenaria ciliata species complex analyzed in this study, occurring in Swiss Northern Alps and in the Jura Mountains (2c, pg of DNA).