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

Abstract

Aim Plant phylogeographic data from the Patagonian Channels are scant and it is largely unknown how the extensive Quaternary glaciations affected the population dynamics of the region's major vegetation component, that is cushion peat bogs (Magellanic moorland). Whether ice‐age glaciers wiped out all terrestrial plant life or whether some populations persisted in situ remains unclear. We reconstructed the phylogeography of two dominant Patagonian cushion peat bog species, Astelia pumila (G.Forst.) Gaudich. (Asteliaceae) and Donatia fascicularis J.R.Forst. & G.Forst. (Stylidiaceae), to test (a) the hypothesis of a glacial refugium for moorland plants in south‐central Chile and (b) the tabula rasa scenario for the Patagonian Channels. The retrieved phylogeographic patterns were compared with those reported previously for a further cushion peat bog species (Pfanzelt et al., Molecular Ecology 26, 4027–4044), with the objective to provide a broader picture of how West Patagonian moorland plants responded to the Quaternary ice‐ages. Location West and Fuegian Patagonia, and the Falkland Islands (Islas Malvinas), southern South America. Methods DNA sequence data from seven and fourteen, respectively, nuclear loci containing Simple Sequence Repeats of 371 and 328 individuals of the two study species were analysed using population genetic summary statistics, phylogenetic networks and Bayesian and multivariate methods to determine genetic structure. Ecological niche modelling was used to reconstruct the spatial distribution of suitable habitat at the Last Glacial Maximum. Results All A. pumila populations belong to a single population genetic cluster. In the case of D. fascicularis, only the northernmost sampled population from Nahuelbuta (Chile) is genetically distinct, whereas the remainder forms a cluster without much further substructure. According to palaeodistribution models, south‐central Chile offered suitable habitat during the last glacial. Main conclusion Both ecological niche modelling and the very low genetic subdifferentiation are congruent with a tabula rasa scenario for the Patagonian Channels. Populations survived the last glacial in south‐central Chile, in an area to the northwest of the ice sheet. From there, southern regions were recolonized through highly bottlenecked source populations. Other, non‐mutually exclusive factors may have further shaped the population genetic patterns, among them high gene flow mediated by the strong westerly winds.

Genomic footprints of Quaternary colonization and population expansion in the Patagonian‐Fuegian region rules out a separate southern refugium in Tierra del Fuego

“…This is noteworthy because, during the LGM, Tierra del Fuego was not totally covered by ice and thus more suitable for potential periglacial refugia than the heavily glaciated western Patagonia. In line with this, recent molecular studies in plants failed to identify refugia in southwesternmost Patagonia (Pfanzelt et al, 2017, 2019). In this and other cases, the incorporation of multilocus data would be helpful to support further or discard the southern glacial refugia proposed.…”