Ibanez T.,Aix - Marseille University |
Ibanez T.,Institute Agronomique Neo Caledonien IAC |
Munzinger J.,IRD Montpellier |
Gaucherel C.,French Institute of Pondicherry |
And 2 more authors.
Australian Journal of Botany | Year: 2013
A direct consequence of deforestation and forest fragmentation in the tropics is the increased importance of boundaries between forest fragments and savannahs. These boundaries are critical zones for understanding the dynamics of savannahs and forests. In the present study, the spatio-temporal dynamics of a savannah-forest boundary in New Caledonia were inferred from the analyses of vegetation structure and composition along three transects. Remnant savannah trees (Melaleuca quinquenervia (Cav.) S.T.Blake) in the forest part of the transect indicated that the forest edge has shifted towards savannah. This margin-forest expansion hypothesis was reinforced by gradual changes from the forest edge to the forest core in species composition (e.g. increase in the frequency of forest-core species) and population structure (e.g. increase in forest tree-stem diameter). However, sharp changes at the forest edge (mainly the increased frequency of small forest trees) suggested that forest expansion has likely been stopped. This suggested that different phases may alternate in the dynamics of savannah-forest boundaries, including stable phases where the boundary does not move, and unstable phases where the boundary moves or expands towards savannah or forest. Variations in the fire regime as a result of the interactions among climate, fire use by humans and vegetation are likely to drive these dynamics. © CSIRO 2013.
PubMed | Institute Agronomique neo Caledonien IAC, Leiden University, National Autonomous University of Mexico, IRD Montpellier and 2 more.
Type: Journal Article | Journal: Plant, cell & environment | Year: 2016
Increases in drought-induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P
Dowle E.J.,Massey University |
Dowle E.J.,Kansas State University |
Morgan-Richards M.,Massey University |
Brescia F.,Institute Agronomique Neo Caledonien IAC |
Trewick S.A.,Massey University
Molecular Ecology | Year: 2015
The giant edible Placostylus snails of New Caledonia occur across a wide range of environmental conditions, from the dry southwest to the wetter central and northeastern regions. In large, slow-moving animals such as Placostylus, speciation could be assumed to be largely driven by allopatry and genetic drift as opposed to natural selection. We examined variation in shell morphology using geometric morphometrics and genetic structure within two species of Placostylus (P. fibratus, P. porphyrostomus), to determine the drivers of diversity in this group. Despite the current patchy distribution of snails on New Caledonia, both mtDNA and nuclear SNP data sets (>3000 loci) showed weak admixing between populations and species. Shell morphology was concordant with the genetic clusters we identified and had a strong relationship with local environment. The genetic data, in contrast to the morphological data, did not show concordance with climatic conditions, suggesting the snails are not limited in their ability to adapt to different environments. In sympatry, P. fibratus and P. porphyrostomus maintained genetic and morphological differences, suggesting a genetic basis of phenotypic variation. Convergence of shell shape was observed in two adjacent populations that are genetically isolated but experience similar habitat and climatic conditions. Conversely, some populations in contrasting environments were morphologically distinct although genetically indistinguishable. We infer that morphological divergence in the Placostylus snails of New Caledonia is mediated by adaptation to the local environment. © 2015 John Wiley & Sons Ltd.
Isnard S.,IRD Montpellier |
L'huillier L.,Institute Agronomique Neo Caledonien IAC |
Rigault F.,IRD Montpellier |
Jaffre T.,IRD Montpellier
Plant and Soil | Year: 2016
Background: New Caledonia is renowned as one of the world’s most significant biodiversity hotpots. The nutrient-deficiency and cations imbalances of ultramafic soils, which cover a third of the island, harbor a disproportionally high proportion of the plant diversity and endemism of New Caledonia. Scope: This review explores how ultramafic soils have influenced the exceptional endemism and richness of New Caledonia trough the concomitant occurrences of habitat patchiness, climatic instability, environmental gradient, and edaphic heterogeneity of ultramafic soils. We focus on the unique ‘maquis’ vegetation where selective pressures by nutrient deficiency and trace element surplus are at their acme. We aim to synthesize our current understanding of diversification and speciation of lineages that have been phylogenetically studied to date. Conclusions: Fragmentation of the peridotite mantle in isolated massifs, and as such spatial heterogeneity of ultramafic soils types, appear to promote plant endemism and speciation. Repeated independent dispersal events of pre-adapted species and persistence of paleo-endemic lineages have contributed to the phylogenetic diversity and the endemism of the ultramafic flora. Finally, historical climatic instability has caused shifts of rain forest species in refugia thereby favoring the extension of maquis species. © 2016, Springer International Publishing Switzerland.
Majorel C.,Center IRD |
Hannibal L.,Center IRD |
Soupe M.-E.,Center IRD |
Carriconde F.,Institute Agronomique Neo Caledonien IAC |
And 5 more authors.
Molecular Ecology | Year: 2012
The fungus Pisolithus albus forms ectomycorrhizal (ECM) associations with plants growing on extreme ultramafic soils, which are naturally rich in heavy metals such as nickel. Both nickel-tolerant and nickel-sensitive isolates of P. albus are found in ultramafic soils in New Caledonia, a biodiversity hotspot in the Southwest Pacific. The aim of this work was to monitor the expression of genes involved in the specific molecular response to nickel in a nickel-tolerant P. albus isolate. We used pyrosequencing and quantitative polymerase chain reaction (qPCR) approaches to investigate and compare the transcriptomes of the nickel-tolerant isolate MD06-337 in the presence and absence of nickel. A total of 1 071 375 sequencing reads were assembled to infer expression patterns of 19 518 putative genes. Comparison of expression levels revealed that 30% of the identified genes were modulated by nickel treatment. The genes, for which expression was induced most markedly by nickel, encoded products that were putatively involved in a variety of biological functions, such as the modification of cellular components (53%), regulation of biological processes (27%) and molecular functions (20%). The 10 genes that pyrosequencing analysis indicated were induced the most by nickel were characterized further by qPCR analysis of both nickel-tolerant and nickel-sensitive P. albus isolates. Five of these genes were expressed exclusively in nickel-tolerant isolates as well as in ECM samples in situ, which identified them as potential biomarkers for nickel tolerance in this species. These results clearly suggest a positive transcriptomic response of the fungus to nickel-rich environments. The presence of both nickel-tolerant and nickel-sensitive fungal phenotypes in ultramafic soils might reflect environment-dependent phenotypic responses to variations in the effective concentrations of nickel in heterogeneous ultramafic habitats. © 2012 Blackwell Publishing Ltd.
Duron Q.,Aix - Marseille University |
Garcia-Iriarte O.,Aix - Marseille University |
Brescia F.,Institute Agronomique Neo Caledonien IAC |
Vidal E.,Aix - Marseille University
Biological Invasions | Year: 2016
Native frugivores play an important role in native plant community dynamics by participating in seed dispersal. Today many island forests are invaded by introduced omnivores, such as rats, but their role in dispersing native plants is still little known. Here, we evaluated whether native seeds from New-Caledonian rainforests can germinate after passing through an invasive rat digestive tract and compared seed germinability and germination time between seeds ingested by invasive rats and native frugivores. We offered native fruits of Ficus racemigera and Freycinetia sulcata to the rats Rattus rattus and R. exulans, three flying foxes Pteropus spp. and the pigeon Ducula goliath. Our results showed that seeds can germinate after passing through an invasive rat digestive tract, and suggest that rats can disperse seeds of both plant species. However, invasive rats may be less efficient than native frugivores, as more seeds were destroyed when passing through rat digestive tracts than through native frugivores, and because germinability was lower and germination time was longer for seeds passing through invasive rats than through native frugivores. The reduced efficiency of rats may result from their generalized diet, the structure of their digestive tract, and/or their feeding behavior. In New-Caledonian rainforests, dispersal services on both plant species are likely well fulfilled by flying foxes and Ducula pigeons, but rats do not seem to be as efficient dispersers. Consequently, management measures to protect native frugivores should help to conserve seed dispersal services. © 2016 Springer International Publishing Switzerland
Wulff A.S.,University of New Caledonia |
Wulff A.S.,Institute Agronomique neo Caledonien IAC |
Hollingsworth P.M.,Royal Botanic Garden Edinburgh |
Ahrends A.,Royal Botanic Garden Edinburgh |
And 4 more authors.
PLoS ONE | Year: 2013
New Caledonia is a global biodiversity hotspot facing extreme environmental degradation. Given the urgent need for conservation prioritisation, we have made a first-pass quantitative assessment of the distribution of Narrow Endemic Species (NES) in the flora to identify species and sites that are potentially important for conservation action. We assessed the distributional status of all angiosperm and gymnosperm species using data from taxonomic descriptions and herbarium samples. We characterised species as being NES if they occurred in 3 or fewer locations. In total, 635 of the 2930 assessed species were classed as NES, of which only 150 have been subjected to the IUCN conservation assessment. As the distributional patterns of un-assessed species from one or two locations correspond well with assessed species which have been classified as Critically Endangered or Endangered respectively, we suggest that our distributional data can be used to prioritise species for IUCN assessment. We also used the distributional data to produce a map of "Hotspots of Plant Narrow Endemism" (HPNE). Combined, we used these data to evaluate the coincidence of NES with mining activities (a major source of threat on New Caledonia) and also areas of conservation protection. This is to identify species and locations in most urgent need of further conservation assessment and subsequent action. Finally, we grouped the NES based on the environments they occurred in and modelled the habitat distribution of these groups with a Maximum Entropy Species Distribution Model (MaxEnt). The NES were separable into three different groups based primarily on geological differences. The distribution of the habitat types for each group coincide partially with the HPNE described above and also indicates some areas which have high habitat suitability but few recorded NES. Some of these areas may represent under-sampled hotspots of narrow endemism and are priorities for further field work. © 2013 Wulff et al.
PubMed | University of Kentucky, CNRS Laboratory of Plant Reproduction and Development, University of New Caledonia and Institute Agronomique neo Caledonien IAC
Type: | Journal: Annals of botany | Year: 2017
Recent parsimony-based reconstructions suggest that seeds of early angiosperms had either morphophysiological or physiological dormancy, with the former considered as more probable. The aim of this study was to determine the class of seed dormancy present in Amborella trichopoda, the sole living representative of the most basal angiosperm lineage Amborellales, with a view to resolving fully the class of dormancy present at the base of the angiosperm clade.Drupes of A. trichopoda without fleshy parts were germinated and dissected to observe their structure and embryo growth. Pre-treatments including acid scarification, gibberellin treatment and seed excision were tested to determine their influence on dormancy breakage and germination. Character-state mapping by maximum parsimony, incorporating data from the present work and published sources, was then used to determine the likely class of dormancy present in early angiosperms.Germination in A. trichopoda requires a warm stratification period of at least approx. 90 d, which is followed by endosperm swelling, causing the water-permeable pericarp-mesocarp envelope to split open. The embryo then grows rapidly within the seed, to radicle emergence some 17 d later and cotyledon emergence after an additional 24 d. Gibberellin treatment, acid scarification and excision of seeds from the surrounding drupe tissues all promoted germination by shortening the initial phase of dormancy, prior to embryo growth.Seeds of A. trichopoda have non-deep simple morphophysiological dormancy, in which mechanical resistance of the pericarp-mesocarp envelope plays a key role in the initial physiological phase. Maximum parsimony analyses, including data obtained in the present work, indicate that morphophysiological dormancy is likely to be a pleisiomorphic trait in flowering plants. The significance of this conclusion for studies of early angiosperm evolution is discussed.
PubMed | Center for Pacific Crops and Trees, Institute Agronomique neo Caledonien IAC, British Petroleum, Bioversity International and 2 more.
Type: Journal Article | Journal: PloS one | Year: 2016
This study aims to understand the genetic diversity of traditional Oceanian starchy bananas in order to propose an efficient conservation strategy for these endangered varieties. SSR and DArT molecular markers are used to characterize a large sample of Pacific accessions, from New Guinea to Tahiti and Hawaii. All Pacific starchy bananas are shown of New Guinea origin, by interspecific hybridization between Musa acuminata (AA genome), more precisely its local subspecies M. acuminata ssp. banksii, and M. balbisiana (BB genome) generating triploid AAB Pacific starchy bananas. These AAB genotypes do not form a subgroup sensu stricto and genetic markers differentiate two subgroups across the three morphotypes usually identified: Iholena versus Popoulu and Maoli. The Popoulu/Maoli accessions, even if morphologically diverse throughout the Pacific, cluster in the same genetic subgroup. However, the subgroup is not strictly monophyletic and several close, but different genotypes are linked to the dominant genotype. One of the related genotypes is specific to New Caledonia (NC), with morphotypes close to Maoli, but with some primitive characters. It is concluded that the diffusion of Pacific starchy AAB bananas results from a series of introductions of triploids originating in New Guinea area from several sexual recombination events implying different genotypes of M. acuminata ssp. banksii. This scheme of multiple waves from the New Guinea zone is consistent with the archaeological data for peopling of the Pacific. The present geographic distribution suggests that a greater diversity must have existed in the past. Its erosion finds parallels with the erosion of cultural traditions, inexorably declining in most of the Polynesian or Melanesian Islands. Symmetrically, diversity hot spots appear linked to the local persistence of traditions: Maoli in New Caledonian Kanak traditions or Iholena in a few Polynesian islands. These results will contribute to optimizing the conservation strategy for the ex-situ Pacific Banana Collection supported collectively by the Pacific countries.
PubMed | Institute Agronomique neo Caledonien IAC, Koniambo Nickel SAS KNS, University of New Caledonia, Aix - Marseille University and 2 more.
Type: Journal Article | Journal: Molecular ecology | Year: 2016
Microbial species richness and assemblages across ultramafic ecosystems were investigated to assess the relationship between their distributional patterns and environmental traits. The structure of microorganism communities in the Koniambo massif, New Caledonia, was investigated using a metagenetic approach correlated with edaphic and floristic factors. Vegetation cover and soil properties significantly shaped the large phylogenetic distribution of operational taxonomic unit within microbial populations, with a mean per habitat of 3.477 (317) for bacteria and 712 (43) for fungi. Using variance partitioning, we showed that the effect of aboveground vegetation was the most significant descriptor for both bacterial and fungal communities. The floristic significant predictors explained 43% of the variation for both the bacterial and fungal community structures, while the edaphic significant predictors explained only 32% and 31% of these variations, respectively. These results confirm the previous hypothesis that the distribution of microorganisms was more structured by the vegetation cover rather than the edaphic characteristics and that microbial diversity is not limited in ultramafic ecosystems.