Molecular analysis and comparative morphology to resolve a complex of cryptic Xiphinema species

Abstract

P. (2010). Molecular analysis and comparative morphology to resolve a complex of cryptic Xiphinema species. -Zoologica Scripta, 39, 483-498.During nematode surveys in cultivated and natural environments in southern Spain nine populations of parthenogenic Xiphinema species tentatively identified as Xiphinema cf. pyrenaicum and one population morphologically close to Xiphinema turcicum were detected. Surveys in southern France also identified one population resembling X. pyrenaicum. We developed a comparative study among these related Xiphinema species, including topotypes of two species of this group previously synonymized, viz. Xiphinema hispanum and Xiphinema sphaerocephalum, by considering morphological and morphometrical features together with molecular data from nuclear ribosomal RNA genes (D2-D3 expansion segments of 28S, ITS1, and partial 18S). Morphological and morphometrical results identified eight of the Spanish populations as Xiphinema nuragicum (previously synonymized with X. pyrenaicum) whereas the ninth population was identified as Xiphinema adenohystherum (also synonymized with X. pyrenaicum). The species X. adenohystherum, X. nuragicum, X. pyrenaicum, and X. sphaerocephalum were shown to be morphologically almost indistinguishable but clearly separated by phylogenetic analyses, thus constituting a complex of cryptic species. Consequently, X. adenohystherum, X. nuragicum, and X. sphaerocephalum were re-established as valid species. Similarly, X. hispanum (morphologically similar to X. aceri) was also shown as a valid species. Xiphinema turcicum, morphologically related to X. pyrenaicum complex by its rounded tail, uterus with a pseudo-Z-differentiation and small spines, was phylogenetically distant to these species based on D2-D3 expansion segments of 28S and ITS1, which suggests a morphological convergence in their evolution.

A phylogenetic assessment of the colonisation patterns in Spauligodon atlanticus Astasio-Arbiza et al., 1987 (Nematoda: Oxyurida: Pharyngodonidae), a parasite of lizards of the genus Gallotia Boulenger: no simple answers

“…As already reported (Blouin, 2002;Gutiérrez-Gutiérrez et al, 2010), the 18S rRNA presents limited variation for resolving nematode relationships either between closely related species or at the intraspecific level. However, when assessing deeper relationships between S. atlanticus and other nematodes, this marker is very useful for an initial molecular identification.…”

“…However, parasites often present a simplified morphology, and molecular techniques are starting to show that many presumed single species actually consist of genetically different parasite lineages, suggestive of cryptic species (Blouin, 2002;Miura et al, 2005;Gutiérrez-Gutiérrez et al, 2010). The lack of morphological differentiation between related parasite species may be due to similar selective pressures promoting morphological convergence in species that are not closely related (Banks & Paterson, 2005).…”

Prevalence, polyphasic identification, and molecular phylogeny of dagger and needle nematodes infesting vineyards in southern Spain

“…Abbreviations are defined in Jairajpuri and Ahmad (1992) characterized by Gutiérrez-Gutiérrez et al (2010). Sequences for X. hispidum, X. lupini, L. alvegus and L. magnus were obtained for these species in this study.…”

Morphological and molecular characterisation of Helicotylenchus pseudorobustus (Steiner, 1914) Golden, 1956 and related species (Tylenchida: Hoplolaimidae) with a phylogeny of the genus

“…As a result, taxonomic difficulties often arise from under-or over-estimation of intraspecific variability of certain mor phological characters that are currently used for species diagnosis. The existence in Helicotylenchus and other ge nera of plant-parasitic nematodes of species complexes, which are morphologically almost indistinguishable but may be phylogenetically distant from one another, has been revealed by molecular studies and complicates the identification of these nematodes (Oliveira et al, 2006;Gutierrez-Gutierrez et al, 2010;Cantalapiedra-Navarrete et al, 2013). In recent years, sequences of nuclear ribosomal RNA gene (rRNA) have been used for molecular characterisation and reconstruction of phylogenetic rela tionships within the Hoplolaimidae and especially within Helicotylenchus (Subbotin et al, 2007(Subbotin et al, , 2011Bae et al, 2009;Flolterman et al, 2009).…”