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Mitchell, Edward

Nom
Mitchell, Edward
Affiliation principale
Site web
Fonction
Professeur ordinaire
Email
edward.mitchell@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/357
_
0000-0003-0358-506X

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  • Publication
    Accès libre
    Effect of taxonomic resolution on ecological and palaeoecological inference: a test using testate amoeba water table depth transfer functions
    Mitchell, Edward 
    ;
    Lamentowicz, Mariusz
    ;
    Payne, Richard J
    ;
    Mazei, Yuri
    Sound taxonomy is a major requirement for quantitative environmental reconstruction using biological data. Transfer function performance should theoretically be expected to decrease with reduced taxonomic resolution. However for many groups of organisms taxonomy is imperfect and species level identification not always possible. We conducted numerical experiments on five testate amoeba water table (DWT) transfer function data sets. We sequentially reduced the number of taxonomic groups by successively merging morphologically similar species and removing inconspicuous species. We then assessed how these changes affected model performance and palaeoenvironmental reconstruction using two fossil data sets. Model performance decreased with decreasing taxonomic resolution, but this had only limited effects on patterns of inferred DWT, at least to detect major dry/wet shifts. Higher-resolution taxonomy may however still be useful to detect more subtle changes, or for reconstructed shifts to be significant.
  • Publication
    Accès libre
    Assessing the ecological value of small testate amoebae (<45 μm) in New Zealand peatlands
    McKeown, Michelle M
    ;
    Wilmshurst, Janet M
    ;
    Duckert, Clément
    ;
    Wood, Jamie R
    ;
    Mitchell, Edward 
    Methodological advances are essential for robust ecological research. Quantitative reconstructions of environmental conditions using testate amoebae rely on sound taxonomy. While the taxonomy of large species is relatively well resolved, this is not the case for most small taxa (typically <45 μm long). In New Zealand, peatlands contain a diversity of both cosmopolitan and characteristic large southern endemic taxa, but also have a high abundance of small taxa. The latter are often lumped into morphotypes reducing their value as ecological indicators. In this study, we demonstrate how (a) lumping small taxa versus splitting them into unique types, and (b) including or excluding them from community analysis influenced their ecological inference. We assessed testate amoeba composition in six peat bogs from New Zealand, three that were moderately-to-highly impacted, and three that were non-impacted. Environmental variables were measured at each sampling site and the surface testate amoeba community patterns and community-environment relationships compared. We found a clear division between impacted and non-impacted sites. Several distinct small taxa were more strongly related to water-table depth and conductivity, while the larger taxa were more correlated to pH. These results show that improved taxonomic resolution of small taxa can provide more informed environmental assessment.
  • Publication
    Accès libre
    Using DNA-barcoding for sorting out protest species complexes:: A case study of the Nebela tincta–collaris–bohemica group (Amoebozoa; Arcellinida, Hyalospheniidae)
    Kosakyan, Anush 
    ;
    Gomaa, Fatma
    ;
    Mitchell, Edward 
    ;
    Heger, Thierry J.
    ;
    Lara, Enrique 
    Species identification by means of morphology is often problematic in protists. Nebela tincta–collaris–bohemica (Arcellinida) is a species complex of small to medium-sized (ca.100 μm) testate amoebae common in peat bogs and forest soils. The taxonomic validity of characters used to define species within this group is debated and causes confusion in studies of biogeography, and applications in palaeoecology.
    We examined the relationship between morphological and genetic diversity within this species complex by combined analyses of light microscopy imaging and Cytochrome Oxidase Subunit 1(COI) sequences obtained from the same individual amoeba cells. Our goals were (1) to clarify the taxonomy and the phylogenetic relationships within this group, and (2) to evaluate if individual genotypes corresponded to specific morphotypes and the extent of phenotypic plasticity.
    We show here that small variations in test morphology that have been often overlooked by traditional taxonomy correspond to distinct haplotypes. We therefore revise the taxonomy of the group. We redefine Nebela tincta (Leidy) Kosakyan et Lara and N. collaris (Ehrenberg 1848) Kosakyan et Gomaa, change N. tincta var. rotunda Penard to N. rotunda (Penard 1890), describe three new species: N. guttata n. sp. Kosakyan et Lara, N. pechorensis n. sp. Kosakyan et Mitchell, and N. aliciae n. sp. Mitchell et Lara.