title: Phylogeography and palaeodistribution modelling of Nassauvia subgenus Strongyloma (Asteraceae): exploring phylogeographical scenarios in the Patagonian steppe.
abstract: The Patagonian steppe is an immense, cold, arid region, yet phylogeographically understudied. Nassauvia subgen. Strongyloma is a characteristic element of the steppe, exhibiting a continuum of morphological variation. This taxon provides a relevant phylogeographical model not only to understand how past environmental changes shaped the genetic structure of its populations, but also to explore phylogeographical scenarios at the large geographical scale of the Patagonian steppe. Here, we (1) assess demographic processes and historical events that shaped current geographic patterns of haplotypic diversity; (2) analyze hypotheses of isolation in refugia, fragmentation of populations, and/or colonization of available areas during Pleistocene glaciations; and (3) model extant and palaeoclimatic distributions to support inferred phylogeographical patterns. Chloroplast intergenic spacers, rpl32-trnL and trnQ-5'rps16, were sequenced for 372 individuals from 63 populations. Nested clade analysis, analyses of molecular variance, and neutrality tests were performed to assess genetic structure and range expansion. The present potential distribution was modelled and projected onto a last glacial maximum (LGM) model. Of 41 haplotypes observed, ten were shared among populations associated with different morphological variants. Populations with highest haplotype diversity and private haplotypes were found in central-western and south-eastern Patagonia, consistent with long-term persistence in refugia during Pleistocene. Palaeomodelling suggested a shift toward the palaeoseashore during LGM; new available areas over the exposed Atlantic submarine platform were colonized during glaciations with postglacial retraction of populations. A scenario of fragmentation and posterior range expansion may explain the observed patterns in the center of the steppe, which is supported by palaeomodelling. Northern Patagonian populations were isolated from southern populations by the Chubut and the Deseado river basins during glaciations. Pleistocene glaciations indirectly impacted the distribution, demography, and diversification of subgen. Strongyloma through decreased winter temperatures and water availability in different areas of its range.
authors.affiliation: Instituto de Botánica Darwinion C.C. 22, B1642HYD, San Isidro, Provincia de Buenos Aires, Argentina.
authors.forename: Marcela V
authors.initials: MV
authors.lastname: Nicola
authors.affiliation: Instituto de Botánica Darwinion C.C. 22, B1642HYD, San Isidro, Provincia de Buenos Aires, Argentina.
authors.forename: Silvana M
authors.initials: SM
authors.lastname: Sede
authors.affiliation: Instituto de Botánica Darwinion C.C. 22, B1642HYD, San Isidro, Provincia de Buenos Aires, Argentina.
authors.forename: Raúl
authors.initials: R
authors.lastname: Pozner
authors.affiliation: Department of Biology and Bean Life Science Museum, Brigham Young University 4102 LSB, Provo, Utah, 84602, USA.
authors.forename: Leigh A
authors.initials: LA
authors.lastname: Johnson
keywords: Colonization; Patagonian steppe; Pleistocene glaciations; fragmentation; glacial refugia; plant phylogeography; range expansion; species distribution modelling