Phylogeography and palaeodistribution modelling in the Patagonian steppe: the case of Mulinum spinosum (Apiaceae)

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

Journal of Biogeography

John Wiley & Sons

Año: 2012 vol. 39 p. 1041 - 1057

1365-2699

Aim An integrative study of the endemic, yet ubiquitous Patagonian shrub Mulinum spinosum (Apiaceae) was performed to assess the historical processes that influenced its geographical pattern of genetic variation; to test the hypotheses of glacial refugia or in situ survival during glacial cycles; and to model extant and palaeoclimatic distributions to assess support for the phylogeographical patterns recovered. Location Chilean and Argentinean Andean region and Patagonian steppe. Methods Chloroplast DNA sequences, trnH?psbA, trnS?trnG and 3?trnV?ndhC, were obtained for 314 individuals from 71 populations. The haplotype data matrix was analysed using nested clade analysis (NCA) to construct a network. Analyses of molecular variance (AMOVA and SAMOVA) and neutrality tests were also used to test for genetic structure and range expansion. The present potential geographical distribution of Mulinum spinosum was modelled and projected onto a Last Glacial Maximum (LGM) model.2 Results Amongst the 29 haplotypes observed, one was widely distributed, but most were restricted to either northern or southern regions. The populations with highest haplotype diversity were found in southern Patagonia, the high Andean region, and northern Patagonia. AMOVA and SAMOVA showed latitudinal structure for Argentinean populations. NCA inferred patterns of restricted gene flow or dispersal but with some long distance dispersal and also long distance colonization and/or past fragmentation. Neutrality tests did not support range expansions. The current distribution model was a fairly good representation of the extant geographical distribution of the species, and the distribution model for the LGM did not show important shifts of the extant range to lower latitudes, except for a shift towards the palaeo seashore. Main conclusions Based on agreement amongst phylogeographical patterns, distribution of genetic variability, equivocal evidence of putative refugia, and palaeodistribution modelling, it is probable that glaciations did not greatly impact the distribution of Mulinum spinosum. Our results are consistent with the in situ survival hypothesis, and not with the latitudinal migration of plant communities to avoid adverse climate conditions during Pleistocene glaciations. It is possible that populations of northern Patagonia may have been isolated from the southern ones by the Chubut and Deseado basins.