No abstract

Petunia is endemic to South America grasslands; member of this genus exhibit variation in flower colour and shape, attracting bees, hawkmoths or hummingbirds. This group of plants is thus an excellent model system for evolutionary studies of diversification associated with pollinator shifts. Our aims were to identify the legitimate pollinator of Petunia secreta, a rare and endemic species, and to assess the importance of floral traits in pollinator attraction in this Petunia species. To determine the legitimate pollinator, field observations were conducted, and all floral visitors were recorded and evaluated. We also measured the nectar volume and sugar concentration. To characterize morphological cues for pollinators, we assessed the ultraviolet (UV)-light response in detached flowers, and characterized the floral pigments and pollen volatile scents for four different Petunia species that present different pollination syndromes. Petunia secreta shares the most recent ancestor with a white hawkmoth-pollinated species, P. axillaris, but presents flavonols and anthocyanin pigments responsible for the pink corolla colour and UV-light responses that are common to bee-pollinated Petunia species. Our study showed that a solitary bee in the genus Pseudagapostemon was the most frequent pollinator of P. secreta, and these bees collect only pollen as a reward. Despite being mainly bee-pollinated, different functional groups of pollinators visit P. secreta. Nectar volume, sugar concentration per flower, morphology and components of pollen scent would appear to be attractive to several different pollinator groups. Notably, the corolla includes a narrow tube with nectar at its base that cannot be reached by Pseudagapostemon, and flowers of P. secreta appear to follow an evolutionary transition, with traits attractive to several functional groups of pollinators. Additionally, the present study shows that differences in the volatiles of pollen scent are relevant for plant mutualistic and antagonist interactions in Petunia species and that pollen scent profile plays a key role in characterizing pollination syndromes.

Hybridization between closely related plant species is a widespread phenomenon with significant evolutionary consequences, so natural hybrid zones provide exciting opportunities to study the processes of genetic differentiation and species formation. In Petunia, genetics, ecology and evolution of pollination syndromes have been thoroughly studied and related to the development of prezygotic isolation barriers between species. However, to date, no studies have explored the importance of extrinsic post-zygotic barriers such as environmental selection as drivers of reproductive isolation. In this study, we applied a population genetics approach to understand the speciation of two partially sympatric taxa of Petunia Juss that hybridize in the wild despite having strong differences in pollination syndrome, mating system and environmental requirements. We evaluated 58 individuals from seven allopatric and two contact zones of Petunia axillaris and P. exserta with genomic data to study the population genetic structure and gene exchange between these species and scan for potential loci under natural selection related to the preservation of species barriers. We explicitly evaluated the time, intensity and direction of interspecific migration, testing for alternative demographic scenarios. The genetic structure showed well-differentiated species-level lineages, and poor differentiation among populations of P. axillaris; P. exserta populations were highly structured, with several well-differentiated intraspecific lineages. Our data provide evidence for admixture with low asymmetric gene flow from P. axillaris to P. exserta associated with recent secondary contact, suggesting that pollinator specificity is not the only trait responsible for species integrity in this system. Combining the results from FST outlier and genotype–phenotype association methods, we identified 54 non-synonymous candidate variants under natural selection. Those variants are found in 35 coding sequences from which we found genes related to light-response networks, supporting that extrinsic factors such as habitat preferences can also provide a mechanism of reproductive isolation between Petunia spp. We argue that a set of pre- and post-zygotic barriers in conjunction with demographic processes maintain the species integrity.

Background Historical and ecological processes shape patterns of genetic diversity in plant species. Colonization to new environments and geographical landscape features determine, amongst other factors, genetic diversity within- and differentiation between-populations. We analyse the genetic diversity and population structure of Calibrachoa heterophylla to infer the influence of abiotic landscape features on the level of gene flow in this coastal species of the South Atlantic Coastal Plain. Results The C. heterophylla populations located on early-deposited coastal plain regions show higher genetic diversity than those closer to the sea. The genetic differentiation follows a pattern of isolation-by-distance. Landscape features, such as water bodies and wind corridors, and geographical distances equally explain the observed genetic differentiation, whereas the precipitation seasonality exhibits a strong signal for isolation-by-environment in marginal populations. The estimated levels of gene flow suggest that marginal populations had restricted immigration rates enhancing differentiation. Conclusions Topographical features related to coastal plain deposition history influence population differentiation in C. heterophylla. Gene flow is mainly restricted to nearby populations and facilitated by wind fields, albeit without any apparent influence of large water bodies. Furthermore, differential rainfall regimes in marginal populations seem to promote genetic differentiation.

It is predicted that climate change will strongly affect plant distributions in high elevation “sky islands” of tropical Andes. Polylepis forests are a dominant element of the treeline throughout the Andes Cordillera in South America. However, little is known about the climatic factors underlying the current distribution of Polylepis trees and the possible effect of global climate change. The species Polylepis quadrijuga is endemic to the Colombian Eastern Cordillera, where it plays a fundamental ecological role in high-altitude páramo-forest ecotones. We sought to evaluate the potential distribution of P. quadrijuga under future climate change scenarios using ensemble modeling approaches. We conducted a comprehensive assessment of future climatic projections deriving from 12 different general circulation models (GCMs), four Representative Concentration Pathways (R) emissions scenarios, and two different time frames (2041–2060 and 2061–2080). Additionally, based on the future projections, we evaluate the effectiveness of the National System of Protected Natural Areas of Colombia (SINAP) and Páramo Complexes of Colombia (PCC) in protecting P. quadrijuga woodlands. Here, we compiled a comprehensive set of observations of P. quadrijuga and study them in connection with climatic and topographic variables to identify environmental predictors of the species distribution, possible habitat differentiation throughout the geographic distribution of the species, and predict the effect of different climate change scenarios on the future distribution of P. quadrijuga. Our results predict a dramatic loss of suitable habitat due to climate change on this key tropical Andean treeline species. The ensemble Habitat Suitability Modeling (HSM) shows differences in suitable scores among north and south regions of the species distribution consistent with differences in topographic features throughout the available habitat of P. quadrijuga. Future projections of the HSM predicted the Páramo complex “Sumapaz-Cruz Verde” as a major area for the long-term conservation of P. quadrijuga because it provides a wide range of suitable habitats for the different evaluated climate change scenarios. We provide the first set of priority areas to perform both in situ and ex situ conservation efforts based on suitable habitat projections.