Phylogeography and palaeodistribution modelling of Nassauvia subgenus Strongyloma (Asteraceae): exploring phylogeographical scenarios in the Patagonian steppe

NICOLA, M. V.; SEDE, S. M.; POZNER, R.; JOHNSON, L. A.

Ecology and Evolution

Wiley

Año: 2014 vol. 4 p. 4270 - 4286

The Patagonian steppe is an immense, cold, arid region, yet phylogeographicallyunderstudied. Nassauvia subgen. Strongyloma is a characteristic element ofthe steppe, exhibiting a continuum of morphological variation. This taxon providesa relevant phylogeographical model not only to understand how pastenvironmental changes shaped the genetic structure of its populations, but alsoto explore phylogeographical scenarios at the large geographical scale of thePatagonian steppe. Here, we (1) assess demographic processes and historicalevents that shaped current geographic patterns of haplotypic diversity; (2) analyzehypotheses of isolation in refugia, fragmentation of populations, and/orcolonization of available areas during Pleistocene glaciations; and (3) modelextant and palaeoclimatic distributions to support inferred phylogeographicalpatterns. Chloroplast intergenic spacers, rpl32?trnL and trnQ?50rps16, weresequenced for 372 individuals from 63 populations. Nested clade analysis,analyses of molecular variance, and neutrality tests were performed to assessgenetic structure and range expansion. The present potential distribution wasmodelled and projected onto a last glacial maximum (LGM) model. Of 41haplotypes observed, ten were shared among populations associated with differentmorphological variants. Populations with highest haplotype diversity andprivate haplotypes were found in central-western and south-eastern Patagonia,consistent with long-term persistence in refugia during Pleistocene. Palaeomodellingsuggested a shift toward the palaeoseashore during LGM; new availableareas over the exposed Atlantic submarine platform were colonized during glaciationswith postglacial retraction of populations. A scenario of fragmentationand posterior range expansion may explain the observed patterns in the centerof the steppe, which is supported by palaeomodelling. Northern Patagonianpopulations were isolated from southern populations by the Chubut and theDeseado river basins during glaciations. Pleistocene glaciations indirectlyimpacted the distribution, demography, and diversification of subgen. Strongylomathrough decreased winter temperatures and water availability in differentareas of its range.