Contact zones and their consequences: hybridization between two ecologically isolated wild Petunia species

Abstract

Plant hybridization is frequently observed in nature and considered an important driver of angiosperm diversity. Species are thought to arise through the accumulation of morphological and genetic differences that promote their evolutionary independence, even in the presence of hybridization. Natural hybrid zones yield an excellent system to study the outcomes of hybridization in terms of species diversity. Two recently diverged species, Petunia axillaris and P. exserta, show floral differentiation attributed to attraction of varying pollinators. Previous studies suggested natural hybridization between these species to explain morphological floral polymorphisms found among individuals of P. exserta. Here, we analyse genetic and morphological diversity in plants from the contact zone between these species and from isolated populations of each species to evaluate natural hybridization and its consequences. We found that the species' integrity is maintained despite interspecific hybridization and introgression that drove the origin of a new lineage in P. exserta in the contact zones.

What could be the fate of secondary contact zones between closely related plant species?

“…DNA extraction followed a CTAB-based method (Roy et al, 1992), and we screened a set of seven microsatellites previously described for P. hybrida (Bossolini et al, 2011) that are considered informative to identify hybrids between Petunia species and are scattered throughout four of seven Petunia chromosomes (Turchetto et al, 2015b(Turchetto et al, , 2019a. Characteristics of each microsatellite loci are described in Table S3.…”

“…In two of these sites ( Figure 1D; Table S1), individuals with the typical morphology of P. axillaris have been found outside shelters, whereas plants with typical P. exserta morphology are found inside shelters together with a variable number of individuals with intermediary corolla color (Figure 1E). The presence of intermediary colored individuals, recorded for the first time in 2002 (Lorenz-Lenke et al, 2006), has been attributed to an intricate pattern of interspecific hybridization, introgression, and ancestral polymorphism sharing in the contact zones (Lorenz-Lemke et al, 2006;Segatto et al, 2014;Turchetto et al, 2015bTurchetto et al, , 2019a.…”

Species boundary and extensive hybridization and introgression in Petunia

“…Moreover, molecular characterization of genes and processes involved in floral syndromes shifts among Petunia species in general and P. axillaris and P. exserta species in particular (Amrad et al 2016;Sheehan et al 2016;Esfeld et al 2018;Rodrigues et al 2018), demonstrating the importance of a prezygotic barrier to reproductive isolation to maintain the species limits of this group. On the other hand, strong evidence of interspecific hybridization between P. axillaris and P. exserta was also obtained through molecular and morphological characterization, mostly at two sites in Guaritas (Turchetto et al 2019; LM Caballero-Villalobos unpubl. res.…”

Morphological and genetic perspectives of hybridization in two contact zones of closely related species of Petunia (Solanaceae) in southern Brazil

“…Posteriorly, these same individuals were analyzed for nuclear markers, which confirmed their hybrid condition (Turchetto et al 2015b). A more comprehensive sample in Serra do Sudeste for P. exserta revealed that individuals with intermediary corolla colors can also be found in other towers, but in contrast to those collected from CO1 and CO2, these individuals constitute a second evolutionary lineage of P. exserta (Turchetto et al 2019). Corolla shape is different between species based on geometric morphometrics (MC Teixeira unpubl.…”

“…The white, scented, UV-absorbent flowers of P. axillaris preferentially attract the hawkmoths Manduca sexta (Venail et al 2010;Klahre et al 2011), whereas the bright red corollas with the exserted stamens of P. exserta flowers constitute common traits that are present in several birdpollinated species (Proctor et al 1996;Gübitz et al 2009). These morphological differences and ecological peculiarities could indicate the isolation between these sympatric species; however, molecular evidence suggests that interspecific hybridization occurs during each reproductive season (Lorenz-Lemke et al 2006;Segatto et al 2014;Turchetto et al 2015b;2019).…”