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

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.