Yohan Pillon
Institut de recherche pour le développement
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Featured researches published by Yohan Pillon.
Taxon | 2007
Yohan Pillon; Michael F. Fay; Mikael Hedrén; Richard M. Bateman
Patterns of polyploid evolution in the taxonomically controversial Dactylorhiza incarnata/maculata groups were inferred genetically by analyzing 399 individuals from 177 localities for (1) four polymorphic plastid regions yielding aggregate haplotypes and (2) nuclear ribosomal ITS allele frequencies. Concordance between patterns observed in distributions of plastid haplotypes and ITS alleles renders ancestral polymorphism an unlikely cause of genetic variation in diploids and allopolyploids. Combining the degree of concerted evolution in ITS alleles (thought to reflect gene conversion) with inferred parentage provides support for a quadripartite classification of western European allopolyploid dactylorchids according to their respective parentage and relative dates of origin. The older allotetraploids that generally exhibit only one parental ITS allele can be divided into those derived via hybridization between the divergent complexes we now call D. incarnata s.l. and D. fuchsii (e.g., D. majalis) and those derived via hybridization between D. incarnata s.l. and D. maculata (e.g., D. elata). Similarly, the younger allotetraploids that maintain evidence of both parental ITS alleles can be divided into those derived from hybridization between D. incarnata s.l. and D. fuchsii, or perhaps in some cases a diploid species resembling D. saccifera (e.g., D. praetermissa, D. purpurella, D. traunsteineri s.l., D. baltica), and those derived from hybridization between the D. incarnata s.l. and D. maculata groups (e.g., D. occidentalis, D. sphagnicola). Older allotetraploids are inferred to have passed through glacially induced migration bottlenecks in southern Eurasia, whereas at least some younger allotetraploids now occupying northern Europe are inferred to have originated post-glacially and remain sympatric with their parents, a scenario that is largely in agreement with the morphology and ecology of these allotetraploids. ITS conversion is in most cases biased toward the maternal parent, eventually obscuring evidence of the original allopolyploidization event because plastid haplotypes also reflect the maternal contribution. Gene flow appears unexpectedly low among allotetraploids relative to diploids, whereas several mechanisms may assist the gene flow observed across ploidy levels. There is good concordance between (1) the genetically delimited species that are required to accurately represent the inferred evolutionary events and processes and (2) morphologically based species recognized in certain moderately conservative morphological classifications previously proposed for the genus. Further research will seek to improve sampling, especially in eastern Eurasia, and to develop more sensitive markers for distinguishing different lineages within (1) the remarkably genetically uniform D. incarnata group (diploids) and (2) locally differentiated populations of (in some cases unnamed) allotetraploids. (Less)
Frontiers in Plant Science | 2013
Tanguy Jaffré; Yohan Pillon; Sébastien Thomine; Sylvain Merlot
While an excess of metals such as zinc, cadmium or nickel (Ni) is toxic for most plants, about 500 plant species called hyperaccumulators are able to accumulate high amounts of these metals. These plants and the underlying mechanisms are receiving an increasing interest because of their potential use in sustainable biotechnologies such as biofortification, phytoremediation, and phytomining. Among hyperaccumulators, about 400 species scattered in 40 families accumulate Ni. Despite this wide diversity, our current knowledge of the mechanisms involved in Ni accumulation is still limited and mostly restricted to temperate herbaceous Brassicaceae. New Caledonia is an archipelago of the tropical southwest pacific with a third of its surface (5500 km2) covered by Ni-rich soils originating from ultramafic rocks. The rich New Caledonia flora contains 2145 species adapted to these soils, among which 65 are Ni hyperaccumulators, including lianas, shrubs or trees, mostly belonging to the orders Celastrales, Oxalidales, Malpighiales, and Gentianales. We present here our current knowledge on Ni hyperaccumulators from New Caledonia and the latest molecular studies developed to better understand the mechanisms of Ni accumulation in these plants.
Conservation Genetics | 2006
Yohan Pillon; Faridah Qamaruz-Zaman; Michael F. Fay; Frédéric Hendoux; Yves Piquot
Liparis loeselii is a rare and endangered orchid occurring in Europe and north-east America. Genetic diversity and structure of this species in north-west France and the United Kingdom were investigated using amplified fragment length polymorphisms (AFLPs). Although clonality and autogamy are common in L. loeselii, we found moderate to important variability within populations. We observed a significant genetic differentiation between populations occurring in dune slacks and fens. This may be correlated with leaf shape as dune slack individuals are sometimes treated as the distinct variety L. loeselii var. ovata. Genetic differentiation between populations was generally low suggesting that gene flow can occur over long distances and possibly across the English Channel. These results show that populations from dune slacks and fens should be managed separately and that geographically distant populations may be equivalent.
American Journal of Botany | 2012
Ole Seberg; Gitte Petersen; Jerrold I. Davis; J. Chris Pires; Dennis W. Stevenson; Mark W. Chase; Michael F. Fay; Dion S. Devey; Tina Jørgensen; Kenneth J. Sytsma; Yohan Pillon
PREMISE OF THE STUDY The Asparagales, with ca. 40% of all monocotyledons, include a host of commercially important ornamentals in families such as Orchidaceae, Alliaceae, and Iridaceae, and several important crop species in genera such as Allium, Aloe, Asparagus, Crocus, and Vanilla. Though the order is well defined, the number of recognized families, their circumscription, and relationships are somewhat controversial. METHODS Phylogenetic analyses of Asparagales were based on parsimony and maximum likelihood using nucleotide sequence variation in three plastid genes (matK, ndhF, and rbcL) and two mitochondrial genes (atp1 and cob). Branch support was assessed using both jackknife analysis implementing strict-consensus (SC) and bootstrap analysis implementing frequency-within-replicates (FWR). The contribution of edited sites in the mitochondrial genes to topology and branch support was investigated. KEY RESULTS The topologies recovered largely agree with previous results, though some clades remain poorly resolved (e.g., Ruscaceae). When the edited sites were included in the analysis, the plastid and mitochondrial genes were highly incongruent. However, when the edited sites were removed, the two partitions became congruent. CONCLUSIONS Some deeper nodes in the Asparagales tree remain poorly resolved or unresolved as do the relationships of certain monogeneric families (e.g., Aphyllanthaceae, Ixioliriaceae, Doryanthaceae), whereas support for many families increases. However, the increased support is dominated by plastid data, and the potential influence of mitochondrial and biparentially inherited single or low-copy nuclear genes should be investigated.
Molecular Ecology | 2009
Yohan Pillon; Jérôme Munzinger; Hamid Amir; Helen C. F. Hopkins; Mark W. Chase
We reconstructed the evolutionary history of Codia, a plant genus endemic to the New Caledonia biodiversity hotspot in the southwest Pacific, using three single‐copy nuclear genes. It seems likely that more than half of Codia species have a hybrid origin, but in the absence of cytological information, it is not known whether polyploids occur. Adaptation to ultramafic soils is possibly a plesiomorphic character for the entire genus. We found that species of hybrid origin can have some morphological characters absent in putative parental species, that is, they exhibit transgressive phenotypes. There is evidence of considerable range alteration post‐origin in several species because some likely parental species of hybrid taxa no longer co‐occur and are confined to putative rainforest refugia; in some cases, hybrid species do not now co‐occur with either of their parental species. These results have implications for the design of conservation strategies, for example, prioritization of parental species for ex‐situ conservation and preservation of the contact zones between soil types where hybridization is more likely to occur (i.e. conserving the possibility for the process to continue rather than trying to conserve taxa).
Molecular Ecology | 2013
Valérie Poncet; François Munoz; Jérôme Munzinger; Yohan Pillon; Céline Gomez; Marie Couderc; Christine Tranchant-Dubreuil; Serge Hamon; Alexandre de Kochko
Amborella trichopoda Baill. (Amborellaceae, Amborellales), the sole living member of the sister group to all other extant angiosperms, is endemic to New Caledonia. We addressed the intraspecific phylogeography of Amborella by investigating whether its present population genetic structure could be related to its current and past habitats. We found moderate range‐wide genetic diversity based on nuclear microsatellite data and detected four well‐differentiated, geographically distinct genetic groups using Bayesian clustering analyses. We modelled the ecological niche of Amborella based on the current climatic and environmental conditions. The predictive ability of the model was very good throughout the Central East mainland zone, but Amborella was predicted in the northern part of the island where this plant has not been reported. Furthermore, no significant barrier was detected based on habitat suitability that could explain the genetic differentiation across the area. Conversely, we found that the main genetic clusters could be related to the distribution of the suitable habitat at the last glacial maximum (LGM, c. 21 000 years BP), when Amborella experienced a dramatic 96.5% reduction in suitable area. At least two lineages survived in distinct putative refugia located in the Massif des Lèvres and in the vicinity of Mount Aoupinié. Our findings finally confirmed the importance of LGM rainforest refugia in shaping the current intra‐ and interspecific diversity in New Caledonian plants and revealed the possibility of an as yet unreported refugium. The combination of niche modelling and population genetics thereby offered novel insight into the biogeographical history of an emblematic taxon.
BMC Evolutionary Biology | 2013
Yohan Pillon; Jennifer Johansen; Tomoko Sakishima; Srikar Chamala; W. Brad Barbazuk; Eric H. Roalson; Donald K. Price; Elizabeth A. Stacy
BackgroundDNA barcoding of land plants has relied traditionally on a small number of markers from the plastid genome. In contrast, low-copy nuclear genes have received little attention as DNA barcodes because of the absence of universal primers for PCR amplification.ResultsFrom pooled-species 454 transcriptome data we identified two variable intron-less nuclear loci for each of two species-rich genera of the Hawaiian flora: Clermontia (Campanulaceae) and Cyrtandra (Gesneriaceae) and compared their utility as DNA barcodes with that of plastid genes. We found that nuclear genes showed an overall greater variability, but also displayed a high level of heterozygosity, intraspecific variation, and retention of ancient alleles. Thus, nuclear genes displayed fewer species-diagnostic haplotypes compared to plastid genes and no interspecies gaps.ConclusionsThe apparently greater coalescence times of nuclear genes are likely to limit their utility as barcodes, as only a small proportion of their alleles were fixed and unique to individual species. In both groups, species-diagnostic markers from either genome were scarce on the youngest island; a minimum age of ca. two million years may be needed for a species flock to be barcoded. For young plant groups, nuclear genes may not be a superior alternative to slowly evolving plastid genes.
New Phytologist | 2014
Yohan Pillon; Helen C. F. Hopkins; Frédéric Rigault; Tanguy Jaffré; Elizabeth A. Stacy
The causes of the species richness of tropical trees are poorly understood, in particular the roles of ecological factors such as soil composition. The nickel(Ni)-hyperaccumulating tree genus Geissois (Cunoniaceae) from the South-west Pacific was chosen as a model of diversification on different substrates. Here, we investigated the leaf element compositions, spatial distributions and phylogeny of all species of Geissois occurring on New Caledonia. We found that New Caledonian Geissois descended from a single colonist and diversified relatively quickly into 13 species. Species on ultramafic and nonultramafic substrates showed contrasting patterns of leaf element composition and range overlap. Those on nonultramafic substrates were largely sympatric but had distinct leaf element compositions. By contrast, species on ultramafic substrates showed similar leaf element composition, but occurred in many cases exclusively in allopatry. Further, earlier work showed that at least three out of these seven species use different molecules to bind Ni. Geissois qualifies as a cryptic adaptive radiation, and may be the first such example in a lineage of tropical forest trees. Variation in biochemical strategies for coping with both typical and adverse soil conditions may help to explain the diversification and coexistence of tropical forest trees on similar soil types.
Kew Bulletin | 2008
Yohan Pillon; Helen C. F. Hopkins; Jason C. Bradford
SummaryDescriptions, illustrations, distribution maps and conservation assessments are provided for two new species of Cunonia from New Caledonia. Cunonia dickisonii Pillon & H. C. Hopkins is endemic to montane ultramafic scrub at high elevation on Mts Humboldt and Kouakoué. Cunonia koghicola H. C. Hopkins, J. Bradford & Pillon is from wet forest at low to medium elevation in the region of Mt Koghi, and irregularities in leaf shape and venation suggest it may be of hybrid origin. Microendemism on Mt Humboldt and Mt Kouakoué is briefly discussed.
Systematic Botany | 2009
Yohan Pillon; Helen C. F. Hopkins; Jérôme Munzinger; Mark W. Chase
Abstract A phylogenetic analysis was conducted on the tribe Spiraeanthemeae (Cunoniaceae) to clarify relationships of Acsmithia and Spiraeanthemum. Three molecular markers, one plastid region (trnL intron and trnL-trnF intergenic spacer) and two nuclear single copy genes (ncpGS and PHYC), were sequenced for this purpose. The independent analysis of the three markers and a combined analysis all showed that Acsmithia is paraphyletic since Spiraeanthemum is nested within it. A morphological survey of all species in the tribe confirmed the existence of two groups within Acsmithia. One comprises the species from Australia, New Guinea, and A. densiflora from New Caledonia and is characterised by multiple ovules per carpel. The other group contains all the remaining New Caledonian species plus A. vitiensis from Fiji and is characterized by a single ovule per carpel. The study shows that characters previously used to distinguish Acsmithia and Spiraenthemum, phyllotaxy and sexual system, are homoplasious as in several other groups of Cunoniaceae. A broad circumscription of the genus Spiraeanthemum is adopted here that includes the species formerly placed in Acsmithia. Two new combinations are proposed: Spiraeanthemum collinum and Spiraeanthemum meridionale. Spiraeanthemum austrocaledonicum is considered a synonym of Spiraeanthemum densiflorum.