Tabula rasa in the Patagonian Channels? The phylogeography of Oreobolus obtusangulus (Cyperaceae)

Abstract

The extent of the Pleistocene glaciations in the Patagonian Channel region (southwesternmost South America) and their impact on the vegetation there are largely unknown. Whether the regional flora was wiped out completely (tabula rasa) or survived in ice-free pockets (in situ survival) is still an open question. The molecular imprint of either scenario should still be visible in extant populations. Therefore, DNA sequence data of Oreobolus obtusangulus Gaudich. (Cyperaceae) were analysed. This species is an abundant constituent of Patagonian cushion peat bogs, one of the Patagonian Channel region's major vegetation types. Three hundred and eighty-four individuals from 48 populations were sequenced for two chloroplast (ycf3-psaA and trnQ -psbK intergenic spacers) and 14 nuclear loci containing simple sequence repeats (SSRs; microsatellites). Phylogenetic reconstructions and the geographic distribution of genetic diversity revealed that the species was split into three main lineages whose general distributions comprise three separate major regions, that is, south-central Chile, Fuego-Patagonia and the East Patagonian Andes, which probably constitute glacial refugia. Postglacial migration fronts formed a suture zone with high levels of genetic diversity in the Northwest Patagonian Andes, where remnants of a supposedly ancestral lineage were also found to be locally restricted to a single population (Huinay). The heavily glaciated Patagonian Channels were likely recolonized from the northwest, and partly from the south. Although the westernmost Patagonian Channel population (Estero Bachem) harboured private SSR alleles (singletons) and showed slightly elevated genetic diversity, it remained unclear whether this population actually survived in situ. This study helps fill a major gap in reconstructing the Pleistocene vegetation history of West and Andean Patagonia.

Tabula rasa in the Patagonian Channels II: The cushion peat bog species Astelia pumila (Asteliaceae) and Donatia fascicularis (Stylidiaceae) survived the last glacial in south‐central Chile

“…In the case of D. fascicularis , DAPC and Baps results, as well as the latitudinal decline of A prv , indeed suggest southward migration, out of a northwestern source (Figure ; Appendix S4), mirroring post‐glacial population movement in O. obtusangulus (Pfanzelt et al., ). However, some D. fascicularis populations from the central Channel region had also similarly high or even higher levels of N all and A r (but not of A prv ; Figure ) than the populations from Alerce Costero (locality 2) and Cordillera Sarao (locality 3).…”

“…Nonetheless, it is unlikely that lineage divergence within D. fascicularis is of Holocene age, given the high number of segregating SNPs between lineages (Table ). Also, the O. obtusangulus population from Nahuelbuta deserves attention because of its genetic distinctness and its interesting genetic affinities not to other populations from the Coastal Cordillera cushion peat bogs further south, but to populations from the Northeast Patagonian Andes (Pfanzelt et al., ). It can only be speculated whether such an Andes‐Coastal Cordillera connection existed also for D. fascicularis , with subsequent extinction of the Andean population.…”

“…Southern South America (modified from Pfanzelt et al., ). Thin blue lines denote the ice extent at the Last Glacial Maximum ( LGM ), following Singer et al.…”

“…They concluded that the littoral of the Patagonian Channels was recolonized only recently, probably after extinction during the LGM because of ice completely covering the coastline. Nuclear and chloroplast sequence data of the cushion peat bog species Oreobolus obtusangulus (Cyperaceae) indicated overlapping signals of at least two glacial cycles (Pfanzelt, Albach, & von Hagen, ). The Channel populations belong mainly to two widespread genealogical lineages also found outside this region, suggesting extinction of O. obtusangulus from the Channels during the LGM and postglacial recolonization from both the North and the South.…”

“…Both palynological studies (Villagrán, , ) and molecular data on O. obtusangulus (Pfanzelt et al., ) point to the ice‐age displacement of cushion peat bog vegetation and thus a tabula rasa scenario for the Patagonian Channel region. If this is the case also for the two study species examined here, it would be expected that: (a) populations from the Northwest should harbour comparatively higher genetic diversity than populations from the post‐glacially recolonized Patagonian Channels; (b) assuming glacial persistence in a single refugium, no or only very shallow population genetic structure should be observed; (c) ecological niche modelling confirms suitable habitat during the last glacial in south‐central Chile.…”