The Pampas in the southern Neotropics is a vast region with vegetation composed mainly of grasses, and it may be the least‐studied ecosystem in southern South America. Contrary to what was thought until recently, this region is heterogeneous and harbours rich biodiversity and many endemic species; however, little is known about the current geographical distribution and evolution of its plants. Here, we present results from phylogeographical studies on two genera typical of open environments (Petunia and Calibrachoa) that occur in both the Pampas and the high‐altitude grasslands of southern Brazil. The rapid radiations of Petunia and Calibrachoa are examples of how strong selective pressures for different pollinators, coupled with adaptation to edaphic and climatic differences, may drive the diversification of plants in the Pampas. We also discuss factors that could have affected and driven the diversification and speciation of plants in this environment. Further studies, including some focusing on other taxa, are required to characterize the diversification of plant species in this region more accurately. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, ••, ••–••.

BackgroundThe glacial and interglacial cycles that characterized the Quaternary greatly affected the distribution and genetic diversity of plants. In the Neotropics, few phylogeographic studies have focused on coastal species outside of the Atlantic Rainforest. Climatic and sea level changes during the Quaternary played an important role in the evolutionary history of many organisms found in coastal regions. To contribute to a better understanding of plant evolution in this environment in Southern South America, we focused on Calibrachoa heterophylla (Solanaceae), an endemic and vulnerable wild petunia species from the South Atlantic Coastal Plain (SACP).ResultsWe assessed DNA sequences from two cpDNA intergenic spacers and analyzed them using a phylogeographic approach. The present phylogeographic study reveals the influence of complex geologic and climatic events on patterns of genetic diversification. The results indicate that C. heterophylla originated inland and subsequently colonized the SACP; the data show that the inland haplogroup is more ancient than the coastal one and that the inland was not affected by sea level changes in the Quaternary. The major diversification of C. heterophylla that occurred after 0.4 Myr was linked to sea level oscillations in the Quaternary, and any diversification that occurred before this time was obscured by marine transgressions that occurred before the coastal sand barrier’s formation. Results of the Bayesian skyline plot showed a recent population expansion detected in C. heterophylla seems to be related to an increase in temperature and humidity that occurred at the beginning of the Holocene.ConclusionsThe geographic clades have been formed when the coastal plain was deeply dissected by paleochannels and these correlate very well with the distributional limits of the clades. The four major sea transgressions formed a series of four sand barriers parallel to the coast that progressively increased the availability of coastal areas after the regressions and that may have promoted the geographic structuring of genetic diversity observed today. The recent population expansion for the entire species may be linked with the event of marine regression after the most recent sea transgression at ~5 kya.

We studied the karyotypes of four Brazilian Cestrum species (C. amictum, C. intermedium, C. sendtnerianum and C. strigilatum) using conventional Feulgen staining, C-Giemsa and C-CMA 3 /DAPI banding, induction of cold-sensitive regions (CSRs) and fluorescent in situ hybridization (FISH) with rDNA probes. We found that the karyotypes of all four species was 2n = 2x = 16, with, except for the eighth acrocentric pair, a predominance of meta-and submetacentric chromosomes and various heterochromatin classes. Heterochromatic types previously unreported in Cestrum as neutral C-CMA 3 0 /DAPI 0 bands, CMA 3 + bands not associated with NORs, and C-Giemsa/CSR/DAPI -bands were found. The heterochromatic blocks varied in size, number, position and composition. The 45S rDNA probe preferentially located in the terminal and subterminal regions of some chromosomes, while 5S rDNA appeared close to the centromere of the long arm of pair 8. These results suggest that karyotype differentiation can occur mainly due to changes in repetitive DNA, with little modification in the general composition of the conventionally stained karyotype.

BackgroundQuaternary climatic changes led to variations in sea level and these variations played a significant role in the generation of marine terrace deposits in the South Atlantic Coastal Plain. The main consequence of the increase in sea level was local extinction or population displacement, such that coastal species would be found around the new coastline. Our main goal was to investigate the effects of sea level changes on the geographical structure and variability of genetic lineages from a Petunia species endemic to the South Atlantic Coastal Plain. We employed a phylogeographic approach based on plastid sequences obtained from individuals collected from the complete geographic distribution of Petunia integrifolia ssp. depauperata and its sister group. We used population genetics tests to evaluate the degree of genetic variation and structure among and within populations, and we used haplotype network analysis and Bayesian phylogenetic methods to estimate divergence times and population growth.ResultsWe observed three major genetic lineages whose geographical distribution may be related to different transgression/regression events that occurred in this region during the Pleistocene. The divergence time between the monophyletic group P. integrifolia ssp. depauperata and its sister group (P. integrifolia ssp. integrifolia) was compatible with geological estimates of the availability of the coastal plain. Similarly, the origin of each genetic lineage is congruent with geological estimates of habitat availability.ConclusionsDiversification of P. integrifolia ssp. depauperata possibly occurred as a consequence of the marine transgression/regression cycles during the Pleistocene. In periods of high sea level, plants were most likely restricted to a refuge area corresponding to fossil dunes and granitic hills, from which they colonized the coast once the sea level came down. The modern pattern of lineage geographical distribution and population variation was established by a range expansion with serial founder effects conditioned on soil availability.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-015-0363-8) contains supplementary material, which is available to authorized users.

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The genus Calibrachoa (Solanaceae) comprises approximately 27 species that are found in open areas of southern South America, with the exception of C. parviflora, which also occurs in North America and Europe, probably as a result of introduction from South America and subsequent naturalization. The genus is closely related to Petunia, but differs in characteristics such as chromosome number, corolla aestivation, seed morphology, and leaf anatomy. Previous publications have shown that C. parviflora and C. pygmaea have morphological, ecological, and molecular features that differ from those of the other species of Calibrachoa, which had also been shown in a phylogenetic study using cpDNA RFLPs. In this paper, we present phylogenies based on chloroplast sequence data from psbB-psbH, trnS-trnG, and trnL-trnF intergenic spacers and the trnL intron, which corroborate the segregation of Calibrachoa species in two highly supported clades. On the basis of these results and the morphological and ecological evidence, we propose that each Calibrachoa clade be recognized at the subgeneric level. A new subgenus, Calibrachoa subg. Stimomphis, is recognized, which includes 25 species, whereas C. parviflora and C. pygmaea are in C. subg. Calibrachoa. A list of species that belong to each subgenus is provided, and lectotypes, neotypes, or epitypes are designated for eight names in Calibrachoa.

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The association of cytogenetic and molecular techniques has contributed to the analysis of chromosome organization and phylogeny in plants. The fluorochrome GC-specific CMA 3 , fluorescent in situ hybridization (FISH) and RAPD (Random Amplified Polymorphic DNA) markers were used to investigate chromosome structure and genetic relationships in Hypochaeris (Asteraceae). Seven species native to South America, and two species introduced from Europe (H. glabra and Hypochaeris sp) were studied. FISH with rDNA probes identified one or two loci of 18S-5.8S-25S rDNA in the South American Hypochaeris species and one locus in the European species. Only one 5S rDNA locus was seen in all species studied. Blocks of GC-rich heterochromatin (CMA-positive bands) associated to 18S-5.8S-25SrDNA loci were detected in all species investigated. Co-location of 5S rDNA and CMA bands was also observed, except for three South American species and Hypochaeris sp. In two South American species, additional CMA bands not related to rDNA were observed on the long arm of chromosome 2, near to the centromere. Hypochaeris glabra exhibited additional CMA-positive signals distributed at pericentromeric regions, on the short arms of all chromosomes. A total of 122 RAPD markers were used to determine the genetic relationships among species. The level of polymorphism was very high, revealing two genetic groups comprising the South American and the European species, thus supporting a previous hypothesis of monophyly of the South American Hypochaeris species. The coefficients of genetic similarity between European and South American species were 0.35, on average. Polymorphism was also high within the two groups. The genetic associations observed with RAPD markers were consistent with chromosome characteristics. Species carrying similar distribution of 45S rDNA loci and CMA-positive signals were included in the same group revealed by RAPDs. Cytogenetic and molecular data support the view that not only chromosome rearrangements, but also changes in DNA sequence took place during the diversification of the South American Hypochaeris species.