Abstract
Identifying the genetic basis of speciation is critical for understanding the evolutionary history of closely related wild species. Recently diverged species facilitate the study of speciation because many genetic and morphological characteristics are still shared by the organisms under study. The Petunia genus grows in South American grasslands and comprises both recently diverged wild species and commercial species. In this work, we analysed two closely related species: Petunia exserta, which has a narrow endemic range and grows exclusively in rocky shelters, and Petunia axillaris, which is widely distributed and comprises three allopatric subspecies. Petunia axillaris ssp. axillaris and P. exserta occur in sympatry, and putative hybrids between them have been identified. Here, we analysed 14 expressed sequence tag-simple sequence repeats (EST-SSRs) in 126 wild individuals and 13 putative morphological hybrids with the goals of identifying differentially encoded alleles to characterize their natural genetic diversity, establishing a genetic profile for each taxon and to verify the presence of hybridization signal. Overall, 143 alleles were identified and all taxa contained private alleles. Four major groups were identified in clustering analyses, which indicated that there are genetic distinctions among the groups. The markers evaluated here will be useful in evolutionary studies involving these species and may help categorize individuals by species, thus enabling the identification of hybrids between both their putative taxa. The individuals with intermediate morphology presented private alleles of their both putative parental species, although they showed a level of genetic mixing that was comparable with some of the individuals with typical P. exserta morphology. The EST-SSR markers scattered throughout the Petunia genome are very efficient tools for characterizing the genetic diversity in wild taxa of this genus and aid in identifying interspecific hybrids based on the presence of private alleles. These properties indicate that these markers will be helpful tools in evolutionary studies.
Highlights
The three subspecies occur in adjacent geographic regions, and the P. axillaris ssp. axillaris could be found in the same narrow region as another congeneric species, Petunia exserta, that presents red and birdpollinated flowers (Lorenz-Lemke et al 2006; Stehmann et al 2009; Segatto et al 2014a) (Fig. 1)
They grow in sympatry, P. exserta and P. axillaris ssp. axillaris are partially isolated in adjacent microhabitats: whereas P. exserta plants grow only inside the shaded cracks of sandstone towers where they are protected from direct rain and sunlight, P. axillaris ssp. axillaris individuals grow in open and sunny habitats (Fig. 1)
The genetic diversity and population structure of these taxa have been previously addressed (LorenzLemke et al 2006; Segatto et al 2014a; Turchetto et al 2014a, b), here we provide a new approach and obtain more precise taxa characterization by using microsatellites derived from expressed sequence tag-simple sequence repeat (EST-SSR) markers
Summary
The Petunia genus encompasses 14 taxonomically accepted wild species, which are distributed exclusively in southern South America (Stehmann et al 2009) and present low genetic variability (Ando et al 2005; Kulcheski et al 2006; Lorenz-Lemke et al 2010; Fregonezi et al 2013), and one artificial hybrid known worldwide, the commercial Petunia hybrida that is the result of crossings between Petunia axillaris and Petunia interior (Segatto et al 2014b). Petunia axillaris is the only species of the genus that presents white corollas (Stehmann et al 2009) and is pollinated by hawkmoths (Ando et al 1995; Venail et al 2010; Klahre et al 2011) (Fig. 1) This species is widespread in the Pampas grasslands of southern South America and currently consists of three taxonomically accepted subspecies: P. axillaris ssp.
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