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The importance of being integrative: a remarkable case of synonymy in the genus Viridiscus (Heterotardigrada: Echiniscidae)

ABSTRACT: There are two predominant sources of taxonomically useful morphological variability in the diverse tardigrade family Echiniscidae: the internal structure and surface sculpture of the cuticular plates covering the dorsum (sculpturing) and the arrangement and morphology of the trunk appendages (chaetotaxy). However, since the appendages often exhibit intraspecific variation (they can be reduced or can develop asymmetrically), sculpturing has been considered more stable at the species level and descriptions of new echiniscid species based solely on morphology are still being published. Here, we present a case study in which a detailed analysis of the morphology and multiple genetic markers of several species of the genus Viridiscus shows that cuticular sculpture may also exhibit considerable intraspecific variation and lead to false taxonomic conclusions. In a population collected from the eastern Nearctic, in the type locality of the recently described species V. miraviridis, individuals with transitional morphotypes between those reported for V. viridissimus and V. miraviridis were found. Importantly, all morphotypes within the viridissimus–miraviridis spectrum were grouped in a single monospecific clade according to rapidly evolving markers (ITS-1, ITS-2 and COI). Given the morphological and genetic evidence, we establish V. miraviridis as a junior synonym of V. viridissimus. This study explicitly demonstrates that a lack of DNA data associated with morphological descriptions of new taxa jeopardizes the efforts to unclutter tardigrade systematics. Additionally, V. perviridis and V. viridissimus are reported from Lâm Đồng Province in southern Vietnam, which considerably broadens their known geographic ranges.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40851-021-00181-z.

SUBMITTER: Gasiorek P

PROVIDER: S-EPMC8605589 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The genus Xiphinema includes a remarkable group of invertebrates of the phylum Nematoda comprising ectoparasitic animals of many wild and cultivated plants. Damage is caused by direct feeding on root cells and by vectoring nepoviruses that cause diseases on several crops. Precise identification of Xiphinema species is critical for launching appropriate control measures. We make available the first detailed information on the diversity and distribution of Xiphinema species infesting wild and cultivated olive in a wide-region in southern Spain that included 211 locations from which 453 sampling sites were analyzed. The present study identified thirty-two Xiphinema spp. in the rhizosphere of olive trees, ten species belonging to Xiphinema americanum-group, whereas twenty-two were attributed to Xiphinema non-americanum-group. These results increase our current knowledge on the biodiversity of Xiphinema species identified in olives and include the description of four new species (Xiphinema andalusiense sp. nov., Xiphinema celtiense sp. nov., Xiphinema iznajarense sp. nov., and Xiphinema mengibarense sp. nov.), and two new records for cultivate olives (X. cadavalense and X. conurum). We also found evidence of remarkable prevalence of Xiphinema spp. in olive trees, viz. 85.0% (385 out of 453 sampling sites), and they were widely distributed in both wild and cultivated olives, with 26 and 17 Xiphinema spp., respectively. Diversity indexes (Richness, Hill´s diversity, Hill´s reciprocal of D and Hill´s evenness) were significantly affected by olive type. We also developed a comparative morphological and morphometrical study together with molecular data from three nuclear ribosomal RNA genes (D2-D3 expansion segments of 28S, ITS1, and partial 18S). Molecular characterization and phylogenetic analyses allowed the delimitation and discrimination of four new species of the genus described herein and three known species. Phylogenetic analyses of Xiphinema spp. resulted in a general consensus of these species groups. This study is the most complete phylogenetic analysis for Xiphinema non-americanum-group species to date.

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The importance of being integrative: a remarkable case of synonymy in the genus Viridiscus (Heterotardigrada: Echiniscidae)

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