Molecular evidence of ice-age refugia in the Patagonia steppe and post-glacial colonisation of the Andes slopes: insights from the endemic species Calceolaria polyrhiza (Calceolariaceae).

COSACOV, A.; SÉRSIC, A.N.; SOSA, V.; JOHNSON, L.; COCUCCI, A.A.

JOURNAL OF BIOGEOGRAPHY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2010 vol. 37 p. 1463 - 1477

0305-0270

Aim We perform a phylogeographical study of an endemic Patagonianherbaceous plant to assess whether geographical patterns of genetic variationcorrespond to in situ Pleistocene survival or to glacial retreat and post-glacialexpansion. We also seek to determine the locations of potential glacial refugia andpost-glacial colonization routes.Location Southern Andes and Patagonian steppe.Methods We used Calceolaria polyrhiza, a widely distributed Patagonianherbaceous plant that occurs mainly in the understorey of Nothofagus rainforests and in the arid Patagonian steppe, as our model system. The chloroplastintergenic spacer trn H?psb A was sequenced for 590 individuals from 68populations. Sequence data were analysed using phylogenetic (maximumparsimony, maximum likelihood and Bayesian inference) and populationgenetic (spatial analyses of molecular variance, mismatch distributions andneutrality tests) methods. Nested clade phylogeographic analyses, and divergencetime estimates using a calibrated molecular clock, were also conducted.Results A total of 27 haplotypes identified in the present study clustered intofour primary genealogical lineages, revealing three significant latitudinalphylogeographical breaks. The two high Andean lineages probably split first,during the late Miocene, and the Patagonian lineage split around 4 Ma,coincident with the establishment of the Patagonian steppe. Within eachhaplogroup, major diversification occurred in the Pleistocene. The Patagoniangroups show a pattern consistent with a rapid post-glacial expansion andcolonization of the Andean flanks, achieved independently by four lineages. Thehighest haplotype diversity was found along a longitudinal transect that isremarkably congruent with the limit of the ice-sheet extension during theGreatest Patagonian Glaciation. A north-east expansion is evident, which isprobably associated with the ?Arid Diagonal? fluctuations.Main conclusions Glacial climate fluctuations had a substantial impact on thediversification, distribution and demography of the study species. A scenario ofmultiple periglacial Pleistocene refugia and subsequent multiple recolonizationroutes, from eastern Patagonia to the Andean flanks, may explain thephylogeographical patterns observed. However, current genetic structure alsopreserves the imprints of older events that probably occurred in the Miocene andPliocene, providing evidence that multiple processes, operating at different spatialand temporal scales, have moulded biodiversity in Patagonia.