Species discovery and diversity in Lobocriconema (Criconematidae: Nematoda) and related plant-parasitic nematodes from North American ecoregions

Abstract

There are many nematode species that, following formal description, are seldom mentioned again in the scientific literature. Lobocriconema thornei and L. incrassatum are two such species, described from North American forests, respectively 37 and 49 years ago. In the course of a 3-year nematode biodiversity survey of North American ecoregions, specimens resembling Lobocriconema species appeared in soil samples from both grassland and forested sites. Using a combination of molecular and morphological analyses, together with a set of species delimitation approaches, we have expanded the known range of these species, added to the species descriptions, and discovered a related group of species that form a monophyletic group with the two described species. In this study, 148 specimens potentially belonging to the genus Lobocriconema were isolated from soil, individually measured, digitally imaged, and DNA barcoded using a 721 bp region of cytochrome oxidase subunit 1 (COI). One-third of the specimens were also analyzed using amplified DNA from the 3' region of the small subunit ribosomal RNA gene (18SrDNA) and the adjacent first internal transcribed spacer (ITS1). Eighteen mitochondrial haplotype groups, falling into four major clades, were identified by well-supported nodes in Bayesian and maximum likelihood trees and recognized as distinct lineages by species delimitation metrics. Discriminant function analysis of a set of morphological characters indicated that the major clades in the dataset possessed a strong morphological signal that decreased in comparisons of haplotype groups within clades. Evidence of biogeographic and phylogeographic patterns was apparent in the dataset. COI haplotype diversity was high in the southern Appalachian Mountains and Gulf Coast states and lessened in northern temperate forests. Lobocriconema distribution suggests the existence of phylogeographic patterns associated with recolonization of formerly glaciated regions by eastern deciduous forest, but definitive glacial refugia for this group of plant parasitic nematodes have yet to be identified. Unlike agricultural pest species of plant-parasitic nematodes, there is little evidence of long-distance dispersal in Lobocriconema as revealed by haplotype distribution. Most haplotype groups were characterized by low levels of intragroup genetic variation and large genetic distances between haplotype groups. The localization of nematode haplotypes together with their characteristic plant communities could provide insight into the historical formation of these belowground biotic communities.

Description and Distribution of Three Criconematid Nematodes from Hangzhou, Zhejiang Province, China

“…Five additional populations of D. limitanea from China have been reported from Guangzhou, Guangdong, Fujian and Yunan provinces. Nematodes from all of these populations have overlapping morphometric ranges, fit well within with the original description and confirm to the species as described by multiple authors (Luc, 1970;Rashid et al, 1986;Rahaman and Ahmed, 1994;Talavera and Hunt, 1997).…”

“…After mounting on stubs, the samples were coated with gold. Specimens from Costa Rica were processed for SEM using the methods described in Powers et al (2010).…”

“…The ML trees used the all sites option for gaps and 200 bootstrap replications to assess clade support. The 18S tree used all the taxa previously presented in Powers et al (2017) plus the eight new sequences from China. The COI tree includes the same taxa as the 18S tree, adding 79 new COI sequences to GenBank, plus 11 new sequences from China.…”

“…The specimen had a body length of 258 µm, spicule of 19 µm, and gubernaculum of 5 µm. In the female, the relatively abrupt constriction of the post-vulval body was not described or illustrated in the original description, but the populations from Malaysia (Sauer and Winoto, 1975), Brazil (Rashid et al, 1986), India (Rahaman and Ahmed, 1994) and Ecuador (Talavera and Hunt, 1997) reported the narrowing of the post-vulval body profile. The…”

Description of Mesocriconema ericaceum n. sp. (Nematoda: Criconematidae) and notes on other nematode species discovered in an ericaceous heath bald community in Great Smoky Mountains National Park, USA

“…Evidence for its distinct status was initially derived from its position on a mitochondrial cytochrome oxidase subunit 1 (COI) phylogenetic tree composed of 550 Mesocriconema nucleotide sequences. This criconematid taxonomic framework has been developed through the combined morphological and molecular analysis of individual nematodes, first documented by differential interference microscopy and morphological measurement, and then 'barcoded' by amplification and nucleotide sequencing of a 721 bp region of COI (Powers et al, 2014(Powers et al, , 2016. In select specimens COI has been sequenced along with ribosomal small subunit 18S rDNA and the internal transcribed spacer 1 (ITS1).…”