New insights into the phylogeny and morphometry of ring nematodes of the subfamily Discocriconemellinae (Nematoda: Criconematidae): Xenocriconemella and Discocriconemella

In this study, we determine the relevance of applying integrative taxonomic approaches for disentangling the underestimation and real nematode biodiversity of Discocriconemellinae (genera Xenocriconemella and Discocriconemella). Our work suggests a new methodology for studying the species boundaries of cryptic species complexes in soil nematodes, by partitioning the morphological variability into body size and body shape variation components. This methodology is applied to delimit species within cryptic species complexes, such as the Xenocriconemella macrodora complex (including Xenocriconemella tica sp. nov.) and a new species complex in the genus Discocriconemella (including two new species, Discocriconemella costaricense sp. nov. and the morphologically analogous Discocriconemella cryptocostaricense sp. nov.) found in a nematode survey carried out in natural forests in Costa Rica. This revealed that consistently, both X. macrodora and D. costaricense species complexes showed heterogeneity only in shape and not in size. Phylogenetic congruence of these species groups was well supported in the phylogenetic analyses of ribosomal and mitochondrial markers. The genus Xenocriconemella was almost the only one that formed a monophyletic lineage within Criconematidae in ribosomal and mitochondrial phylogenetic trees. However, the genus Discocriconemella, including the two new species, formed a paraphyletic distribution between clades of species of this genus with independent lineages, confirming previous studies.