BackgroundThe classification of closely related plants is not straightforward. These morphologically similar taxa frequently maintain their inter-hybridization potential and share ancestral polymorphisms as a consequence of their recent divergence. Under the biological species concept, they may thus not be considered separate species. The Petunia integrifolia complex is especially interesting because, in addition to the features mentioned above, its taxa share a pollinator, and their geographical ranges show multiple overlaps. Here, we combined plastid genome sequences, nuclear microsatellites, AFLP markers, ecological niche modelling, and bioregions analysis to investigate the genetic variability between the different taxa of the P. integrifolia complex in a comprehensive sample covering the entire geographical range of the complex.ResultsResults from molecular markers did not fully align with the current taxonomic classification. Niche modelling and bioregions analyses revealed that taxa were associated with different ecological constraints, indicating that the habitat plays an important role in preserving species boundaries. For three taxa, our analyses showed a mostly conserved, non-overlapping geographical distribution over time. However, for two taxa, niche modelling found an overlapping distribution over time; these taxa were also associated with the same bioregions.ConclusionscpDNA markers were better able to discriminate between Petunia taxa than SSRs and AFLPs. Overall, our results suggest that the P. integrifolia complex represents a continuum of individuals from distant and historically isolated populations, which share some morphological traits, but are established in four different evolutionary lineages.Electronic supplementary materialThe online version of this article (10.1186/s12862-017-1084-y) contains supplementary material, which is available to authorized users.
Petunia patagonica is restricted to the Patagonian region of Argentina and its identity is controversial. The species was described in the genus Nierembergia, and subsequently transferred to the genus Petunia. However, several morphological characteristics of P. patagonica as well as its geographical distribution differ from other Petunia species, and it has been repeatedly considered an exception in the genus. Using one nuclear and two cpDNA markers for 22 species representing seven genera of the tribe Petunieae, we analyzed phylogenetic and biogeographic evidence to clarify the phylogenetic position of P. patagonica. Our results suggest that P. patagonica is not a member of the genus Petunia and is closer to Fabiana imbricata. In addition, Calibrachoa appears basal within the Petunia, Calibrachoa, and Fabiana clades, and Fabiana and Petunia are sister genera. This result led us to reconstruct an ancestral region for this clade within the subtropical grasslands of South America. Subsequent dispersion to the Patagonian and Andean regions was inferred in the divergence of Fabiana and P. patagonica. Our work suggests a need for more studies towards a new generic placement. Ancestral area reconstruction suggests that the origin of the Calibrachoa, Fabiana and Petunia lineages was located in the subtropical grasslands of South America, and the colonization of the Andes and Patagonia seems to be divergent and was achieved only for species belonging to the Fabiana and P. patagonica clades.
Phylogenetic niche conservatism can be investigated at multiple scales on an explicit geographical context. Haplotype-based comparative analyses of lineages occupying the same region, and thus subjected to similar environmental factors, allow decoupling shared evolutionary and ecological patterns, as well as multiple dimensions of adaptive diversification. Here we aimed to assess the role of environmental drivers on diversification of subtropical grassland, based on haplotypic diversity of two plant genera. We sampled two closely related and co-distributed grassland plant genera, Petunia and Calibrachoa, across their entire distribution area. Eigenvectors extracted from pairwise distances based on chloroplast DNA haplotypes were used to fit Phylogenetic Signal-Representation (PSR) curves to estimate evolutionary patterns in 19 bioclimatic variables and altitude. The PSR curves showed that altitude, precipitation, and temperature variables changed at different rates with haplotype differentiation. Altitude and temperature traits evolved under conditions closer to a neutral dynamics, whereas precipitation traits differentiated following more complex models. Our results indicated that the diversification in the two genera was more limited by precipitation conditions. Based on these novel findings, we suggest that future studies should test the possible impact of precipitation variables on the process of ecological differentiation in these genera.
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