Aim The genus Podocarpus (Podocarpaceae) provides an opportunity to contrast biogeographical hypotheses within and among continents, and to analyse divergence between disjunct tropical and temperate forests of South America. We developed a calibrated phylogeny of Podocarpus to reconstruct the ancestral areas and potential expansion routes within Podocarpaceae.Location Podocarpus consists of two extant subgenera: Foliolatus from Asia and Oceania, and Podocarpus located in Gondwanan continents and north to the Caribbean. The paper focuses mainly on the area occupied by the latter subgenus.Methods We combined previously published and novel DNA sequences with fossil records. New species sequenced are members of Podocarpus subgenus Podocarpus from South and Central America. We assembled DNA sequences of the chloroplast (matK and rbcL) and nuclear (ITS1 and ITS2) to analyse phylogenetic relationships within Podocarpus subgenus Podocarpus by Bayesian methods, which were calibrated using macrofossils that could be confidently identified as modern genera. Ancestral areas were inferred using the dispersalextinction-cladogenesis model.
We tested the hypothesis that South Andean populations of the highly polymorphic and mostly Northern Hemisphere perennial forb Cerastium arvense L. show ecotypic variation along distinct habitats. We compared differences in morphology and flowering phenology among six natural populations occurring in different environments. Genetic differences were analyzed by a common-garden experiment and isozyme electrophoresis. Several of the morphological differences observed in the field were maintained after more than a year of cultivation in the common garden (e.g., plant height and leaf width). Mean tests and multivariate analyses on morphological traits generally distinguished high-elevation populations from the rest, and a similar grouping of populations was obtained from isozyme data at 10 loci. Cerastium arvense had genetic polymorphism levels of >50% in all populations and an average genetic diversity (HT = 0.254) of which approximately 20% was distributed among populations. These marked genetic differences are probably maintained by restricted gene flow due to variation in flowering time. Morphological and genetic differences suggest ecotypic variation in C. arvense in the southern Andes, which seems to have originated by disruptive selective pressures in different environments and the effect of genetic drift in response to the extreme climatic changes occurring during the Pleistocene.Key words: common-garden experiment, ecotypic variation, elevation and precipitation, genetic diversity, Patagonian Andes, phenology.
Aim: We sought to determine if the present fragmentary distribution of the giant columnar cactus Echinopsis terscheckii in tropical drylands is a relict of a previously more widespread range during cold and dry phases of the Last Glacial Maximum (LGM).Location: Tropical and subtropical dry ecotonal areas of northern and central Andes of Argentina.
Methods:We combined ecological niche models (ENM) with molecular polymorphisms of isozymes and DNA sequences. We collected samples from 30 individuals at 24 locations for genetic analysis covering a wide range of environmental conditions. We sequenced the nuclear ITS and three non-coding regions of the chloroplast DNA and we resolved 15 isozyme loci. Potential distribution was modelled using 88 E. terscheckii presence training records and a reduced set of 10 modern bioclimatic variables.LGM and the Mid-Holocene distributions were derived by projecting bioclimatic data under present to past environmental conditions according to CCSM4 and MIROC-ESM Global Climate Models.Results: We detected high isozyme diversity towards the south. The multivariate cluster analysis yielded two groups of populations that were geographically concordant with the DNA haplotypes located north and south of a divide at 27°S. Distribution models show range expansion during the LGM in two north and south areas separated by a gap of low suitability at 27°S. Suitable areas in the south were close to current populations, while in the north, populations survived in more disjunct locations that probably suffered from founder effects. In contrast, Mid-Holocene bioclimatic conditions were relatively unsuitable in the south.Main conclusions: Our results suggest that the divergence of north and south groups of E. terscheckii populations reflect long-lasting persistence through climatic cycles that were reinforced by the presence of an orogenic divide at mid-latitudes.Latitudinally divergent groups of populations should be treated as distinct evolutionary significant units that deserve independent conservation actions. Increased genetic diversity and inbreeding towards the south may guide setting up priorities for the long-term protection of a dominant element of drylands as E. terscheckii.
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