Abstract
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.
Highlights
The classification of closely related plants is not straightforward
We found low haplotype sharing among species, with only three haplotypes shared between two species each (Additional file 6: Table S3; Fig. 2): H34 and H41 were shared by P. interior and P. inflata, whereas H43 was observed in P. inflata and P. integrifolia
Our results suggest that the Petunia integrifolia species complex represents four historically isolated lineages
Summary
The 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. Many morphs or ecotypes are associated with geographically distant habitats, where reproductive isolation is a result of the physical separation, rather than arising from biological constraints. In such cases, the partial or full reduction of the gene flow between newly established and ancestral populations could allow the independent evolution and differentiation of their gene pools over time, without necessarily leading to reproductive incompatibility [10]. The sustained potential for interhybridization prevents the use of the biological species concept to define these taxonomical entities
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