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

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.

Natural history of the narrow endemics Ipomoea cavalcantei and I. marabaensis from Amazon Canga savannahs.

Amazon comprises a vast variety of ecosystems, including savannah-like Canga barrens that evolved on iron-lateritic rock plateaus of the Carajás Mountain range. Individual Cangas are enclosed by the rain forest, indicating insular isolation that enables speciation and plant community differentiation. To establish a framework for the research on natural history and conservation management of endemic Canga species, seven chloroplast DNA loci and an ITS2 nuclear DNA locus were used to study natural molecular variation of the red flowered Ipomoea cavalcantei and the lilac flowered I. marabaensis. Partitioning of the nuclear and chloroplast gene alleles strongly suggested that the species share the most recent common ancestor, pointing a new independent event of the red flower origin in the genus. Chloroplast gene allele analysis showed strong genetic differentiation between Canga populations, implying a limited role of seed dispersal in exchange of individuals between Cangas. Closed haplotype network topology indicated a requirement for the paternal inheritance in generation of cytoplasmic genetic variation. Tenfold higher nucleotide diversity in the nuclear ITS2 sequences distinguished I. cavalcantei from I. marabaensis, implying a different pace of evolutionary changes. Thus, Canga ecosystems offer powerful venues for the study of speciation, multitrait adaptation and the origins of genetic variation.