Species boundary and extensive hybridization and introgression in Petunia

Caroline Turchetto,Loreta B Freitas,Carolina K Schnitzler

doi:10.1590/0102-33062019abb0124

Caroline Turchetto, Loreta B Freitas + Show 1 more

Open Access

https://doi.org/10.1590/0102-33062019abb0124

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Abstract

ABSTRACT Studying the role of hybridization in the speciation of plants is one of the most thrilling areas of evolutionary biology. Hybridization in natural populations can act in opposition to divergence, contribute to adaptation through introgression or foster the emergence of new lineages via hybrid speciation. Species of the plant genus Petunia grow in open areas in southern South America. Some natural interspecific hybrid events have been described for the genus, such as between the endemic P. exserta and the widespread P. axillaris. Both species occur in sympatry in Serra do Sudeste (Brazil), where they occur in diverse habitats and exhibit floral divergence, which has been related to the attraction of different primary pollinators. The present study evaluates the maintenance of the species boundaries front of hybridization and introgression. Direct and indirect methods of estimating gene exchange employed genotyping 720 reproductive plants and 611 progenies of both species with eight microsatellite loci. Gene exchange was found to be frequent and bidirectional between the species, indicating that introgression changes their genetic constitution in areas of sympatry. Limits of the studied species are being maintained because of the high level of inbreeding and backcrosses that are habitat-dependent.

Highlights

Gene exchange between closely related species is considered an important driver of diversity in angiosperms (Abbott et al 2016)
Petunia axillaris corollas are white, scented, and UV-absorbent, with reproductive organs included on the corolla, traits associated with hawkmothpollination (Venail et al 2010; Klahre et al 2011); flowers of P. exserta are red, nonfragrant, UV-reflectant and have exserted stamens, characteristics usually attributed to hummingbird-pollination syndrome (Lorenz-Lemke et al 2006)
In the Bayesian analysis of adult individuals, hybrid ancestry was observed more frequently among P. exserta individuals (Fig. 2). These results suggested that fertilization between these species failed when pollen flows from P. exserta to P. axillaris or that the hybrid progeny has a lower success of developing until the adult stage when it is in the P. axillaris microhabitat

Summary

Introduction

Gene exchange between closely related species is considered an important driver of diversity in angiosperms (Abbott et al 2016). P. exserta is endemic to the Serra do Sudeste, to the region known as Guaritas (Fig. 1B; Segatto et al 2014), where both species occupy different microhabitats: P. axillaris occurs on the top and faces of arenitic towers, in sunny and open patches (Fig. 1D), while P. exserta is found inside small cavities (shelters) in those towers (Fig. 1F), with individuals growing totally protected from direct sunlight and rain Both species present long and salverform (hypocrateriform) corolla tubes, erect growth habit, and yellow pollen (Stehmann et al 2009), but they differ in morphological characteristics associated with their pollination syndromes, such as corolla color, scent production, and UV response. Petunia axillaris corollas are white, scented, and UV-absorbent, with reproductive organs included on the corolla, traits associated with hawkmothpollination (Venail et al 2010; Klahre et al 2011); flowers of P. exserta are red, nonfragrant, UV-reflectant and have exserted stamens, characteristics usually attributed to hummingbird-pollination syndrome (Lorenz-Lemke et al 2006)

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