Geography is essential for reproductive isolation between florally diversified morning glory species from Amazon canga savannahs

Elena Babiychuk,Vera Lucia Imperatriz Fonseca,Santelmo Vasconcelos,Sergei Kushnir,Lourival Tyski,José Oswaldo Siqueira,Edilson Freitas Da Silva,Jorge Filipe Dos Santos,José Tasso Felix Guimaraes,Delmo Fonseca Da Silva,Luiza Araújo Romeiro,Alexandre Castilho,Juliana Galaschi Teixeira

doi:10.1038/s41598-019-53853-4

Abstract

The variety, relative importance and eco-evolutionary stability of reproductive barriers are critical to understanding the processes of speciation and species persistence. Here we evaluated the strength of the biotic prezygotic and postzygotic isolation barriers between closely related morning glory species from Amazon canga savannahs. The flower geometry and flower visitor assemblage analyses supported pollination by the bees in lavender-flowered Ipomoea marabaensis and recruitment of hummingbirds as pollinators in red-flowered Ipomoea cavalcantei. Nevertheless, native bee species and alien honeybees foraged on flowers of both species. Real-time interspecific hybridization underscored functionality of the overlap in flower visitor assemblages, questioning the strength of prezygotic isolation underpinned by diversification in flower colour and geometry. Interspecific hybrids were fertile and produced offspring in nature. No significant asymmetry in interspecific hybridization and hybrid incompatibilities among offspring were found, indicating weak postmating and postzygotic isolation. The results suggested that despite floral diversification, the insular-type geographic isolation remains a major barrier to gene flow. Findings set a framework for the future analysis of contemporary evolution of plant-pollinator networks at the population, community, and ecosystem levels in tropical ecosystems that are known to be distinct from the more familiar temperate climate models.

Highlights

The variety, relative importance and eco-evolutionary stability of reproductive barriers are critical to understanding the processes of speciation and species persistence
I. cavalcantei was common in canga N4, whereas I. marabaensis was not abundant and only appeared as groups of 10–20 individuals close to the canga-forest boundaries
It was difficult to compare the historical abundance of I. cavalcantei and I. marabaensis in canga N5, of which only 9% is available for studies[61]

Summary

Introduction

The variety, relative importance and eco-evolutionary stability of reproductive barriers are critical to understanding the processes of speciation and species persistence. The Grant-Stebbins model can explain pollinator-driven floral diversification[40,41,42] In this model, geographical differences in pollinator abundance drive adaptive divergence in floral traits across plant populations leading to pollination ecotypes and establishment of a prezygotic reproductive barrier, the so-called floral isolation[12]. If interspecific hybrids do not suffer severe sterility problems, they can give rise to new homoploid species in plants and birds[50,51]; facilitate genetic rescue and demographic recovery[52,53]; or underpin introgression of favourable traits, the so-called adaptive introgression[54,55], which explains the evolvement of invasiveness[56] and recent adaptations to the changing environment, for example in fish[57]. At the opposite end of the interspecific hybridization effect spectrum is species extinction by genetic and demographic swamping[58]

Methods

Results

Conclusion