Species diversity and speciation mechanisms in Spiranthes (Orchidaceae)

Oral Paper - Session 50: Hybrids and Hybridization: abstract ID. 97Conference Theme: Celebrating Our History, Conserving Our FutureInterspecific hybridization followed by polyploidization is an important speciation mechanism in angiosperms. Orchids are well known for their species richness. We investigate allopolyploid speciation mechanism in Spiranthes, a small orchid genus with several polyploid species and confirmed allopolyploids, such as S. hongkongensis in Asia and S. diluvialis in North America. Our previous work has shown parental additivity and fixed heterozygosity at allozyme loci in the allotetraploid S. hongkongensis. However, responses of repeated rDNA sequences to allopolyploidization are different, as a result of fast concerted evolution. Using mitochondrial DNA, we had earlier shown that the widely occurring Asian species S. sinensis, is the maternal parent of S. hongkongensis. The putative paternal progenitor might be the European species S. spiralis as its range extends eastwards to the Himalayas in western Asia. We hypothesize that the Asian allopolyploid species S. hongkongensis and others might have evolved through natural hybridization in the Himalayan mountain ranges where the white flowered S. spiralis and the pink flowered S. sinensis occur in sympatry. Using nuclear ribosomal ITS markers together with several cpDNA markers, we test the hypotheses about allopolyploid speciation in Asian Spiranthes. We examined rDNA polymorphism and the extent and direction of concerted evolution in the clones of the ITS region in the putative allopolyploid individuals and their diploid progenitors. Among 131 sequenced clones, most clones from S. hongkongensis were similar to the pink-flowered S. sinensis, its maternal diploid progenitor. However, we identified two different rDNA lineages in three individuals from two different populations of S. hongkongensis that were similar to a white-flowered species from India and also occurring in the Himalayas. The data indicate concerted evolution has not proceeded to completion in the allopolyploid S. hongkongensis populations; and the rDNA repeats of the paternal progenitor tend to be lost or converted in different allopolyploids of independent origin, indicating a directional evolution of the rDNA in favor of the maternal genome. Furthermore, our phylogenetic studies of the putative diploid progenitors and allopolyploids uncovered a new species, previously mistaken as synonymous to S. sinensis or S. spiralis. The evolutionary implications of geographical isolation and recurrent allopolyploidization in generating species diversity are discussed. Further studies of the genomic and transcriptomic changes in different allopolyploids can provide new insights into this mode of speciation in flowering plants

Generic delimitation and historical biogeography in the early-divergent 'ambavioid' lineage of Annonaceae: Cananga, Cyathocalyx and Drepananthus

Generic delimitation of Cyathocalyx and Drepananthus has been controversial, with some authors recognizing them as distinct genera, and others recognizing a more broadly defined Cyathocalyx, inclusive of Drepananthus. Some doubt also exists regarding the relationships between these taxa and Cananga. Molecular phylogenetic analyses are presented based on combined psbA-trnH spacer, trnL-F, matK and rbcL sequences. Results indicate that Cananga, Cyathocalyx s.str. and Drepananthus form three generally well-supported clades, although with inadequate resolution of relationships among the three clades. Morphological variation is re-evaluated, and the narrower delimitation of Cyathocalyx proposed, necessitating 21 new nomenclatural combinations following the recognition of Drepananthus as a distinct genus. Divergence times are estimated using an uncorrelated lognormal distributed (UCLD) relaxed molecular clock. Historical biogeographical analysis suggests that the ambavioid lineage originated in Africa, with subsequent dispersal into Asia. Alternative hypotheses for this dispersal, involving rafting on the Indian tectonic plate versus migration via the extensive boreotropical forests associated with the Eocene thermal maximum, are evaluated, and the latter route identified as the most consistent with the divergence age estimates and the geological and palaeoclimatic data.link_to_subscribed_fulltex

Molecular phylogeny of Ceropegia (Asclepiadoideae, Apocynaceae) from Indian Western Ghats

Ceropegia includes more than 200 species distributed in the Old World ranging from the Canary Islands to Australia. In India, there are about 50 species described on a morphological basis as belonging to Ceropegia, and most of them are endemic to the Western Ghats. To investigate evolutionary relationships among Indian Ceropegia taxa and their allies, a phylogenetic analysis was conducted to include 31 Indian taxa of Ceropegia and Brachystelma and their congeners from other geographical regions using nuclear ribosomal internal transcribed spacer (ITS) and three noncoding chloroplast DNA (cpDNA) sequences, including intergenic spacers trnT-L and trnL-F, and trnL intron. The Western Ghats Ceropegia species were found to be most closely related to Indian Brachystelma, with the two genera being placed sister to each other in the ITS phylogeny or with the Brachystelma clade nested within one of the two subclades of Indian Ceropegia in the cpDNA phylogeny. In contrast, Ceropegia species from other regions and African Brachystelma all formed separate clades basal to the Indian Ceropegia-Brachystelma clade. Thus, it can be concluded that the classical morphology-based delineation of the two genera needs revision to reflect their phylogenetic relationships, which are more in accordance with their geographical origin than with morphology. © Springer-Verlag 2009.link_to_subscribed_fulltex

Systematic evaluation of natural phenolic antioxidants from 133 Indian medicinal plants

Total antioxidant capacities of 133 Indian medicinal plant species sampled from 64 families were assessed by ABTS, DPPH and FRAP assays, and their total phenolic contents measured by Folin-Ciocalteu assay. These species exhibited a broad range of antioxidant activities, varying from 0.16 to 500.70 mmol TEAC/100 g DW in the ABTS assay. The antioxidant activity values similarly varied with the DPPH and FRAP assays. Significant and positive linear correlations were found between total antioxidant capacities and phenolic contents (R = 0.89-0.97), indicating that phenolics were the dominant antioxidant constituents in the tested medicinal plants. Preliminary identification of the major phenolic compounds from 83 selected medicinal plants by reversed-phase HPLC revealed phenolic acids, tannins, flavonoids, curcuminoids, coumarins, lignans, and quinines. The fruit of Terminalia chebula, pericarp of Punica granatum and gall of Rhus succedanea showed very high levels of hydrolysable tannins, and the gum of Acacia catechu presented very high levels of catechin and epicatechin in addition to tannins. Major phenolics in many of the medicinal plants were identified for the first time (e.g., Euphorbia lathyrus, Ipomoea turpethum, and Picrorrhiza kurroa). This systematic investigation of a large number of Indian medicinal plants proved important for understanding their chemical constituents and functionality in Ayurvedic medicine, and contributes to the search for natural sources of potent antioxidants. © 2006 Elsevier Ltd. All rights reserved.link_to_subscribed_fulltex