Abstract
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.
Highlights
Plants present remarkable opportunities for studying adaptive radiation and speciation in action[1]
To decipher the phylogenetic affinities of I. cavalcantei and I. marabaensis using molecular markers, partial coding sequences of seven genes encoded by the plastomes were determined and compared to respective sequences computationally extracted from the assembled and sequenced plastomes of twenty six Ipomoea species[15]
It is unlikely that plastidial RNA editing converts CAA codon to a translation termination codon UAA, we infer that rpoC1K and rpoC1Q subunit isoforms characterize the plastidial prokaryotic type RNA polymerase in I. cavalcantei and I. marabaensis
Summary
Plants present remarkable opportunities for studying adaptive radiation and speciation in action[1]. Interactions with pollinators and herbivores[2], adaptation to soils and harsh environmental conditions[3] are among the major ecological factors that drive adaptive radiation in plants Ecogeographic factors such as mountain range uplifts and island formation set gene flow restrictive reproductive isolation barriers in plants and facilitate rapid speciation rates[4]. The primary goals were to: (1) investigate the genetic structure and diversity of I. cavalcantei and I. marabaensis populations; (2) find molecular evidence for the hypotheses that I. cavalcantei and I. marabaensis are recently diverged, sister species[12] that could hybridize in nature; (3) study the role of Canga soils in structuring plant communities and species distributions; (4) establish a framework for the future research on natural history and conservation management of Carajás morning glories
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