The identification of sympatric cryptic free-living nematode species in the Antarctic intertidal

Abstract

The diversity of free-living nematodes in the beaches of two Antarctic islands, King George and Deception islands was investigated. We used morphological and molecular (LSU, and two fragments of SSU sequences) approaches to evaluate 236 nematodes. Specimens were assigned to at least genera using morphology and were assessed for the presence of cryptic speciation. The following genera were identified: Halomonhystera, Litoditis, Enoploides, Chromadorita, Theristus, Oncholaimus, Viscosia, Gammanema, Bathylaimus, Choanolaimus, and Paracanthonchus; along with specimens from the families Anticomidae and Linhomoeidae. Cryptic speciation was identified within the genera Halomonhystera and Litoditis. All of the cryptic species identified live sympatrically. The two cryptic species of Halomonhystera exhibited no significant morphological differences. However, Litoditis species 2 was significantly larger than Litoditis species 1. The utility of molecular data in confirming the identifications of some of the morphologically more challenging families of nematodes was demonstrated. In terms of which molecular sequences to use for the identification of free-living nematodes, the SSU sequences were more variable than the LSU sequences, and thus provided more resolution in the identification of cryptic speciation. Finally, despite the considerable amount of time and effort required to put together genetic and morphological data, the resulting advance in our understanding of diversity and ecology of free-living marine nematodes, makes that effort worthwhile.

Comparison of morphological, DNA barcoding, and metabarcoding characterizations of freshwater nematode communities

“…A similar result was reported in another nematode study, in which a reduced taxonomic assignment was obtained using the dada2 pipeline (Waeyenberge, Sutter, Viaene, & Haegeman, 2019). As the dada2 pipeline uses a more stringent filtering process than the standard OTU-pipeline, it might omit several sequences maintained in the OTU approach, resulting in a much lower number of reads in the final ASV Several initiatives have attempted to curate global biodiversity in public databases for molecular purposes, but these efforts are far from complete (Geiger et al, 2016;Lee et al, 2017). Our study highlights the need to quickly expand molecular databases in order to allow the full use of molecular methods in accurate species assignments.…”

“…Several initiatives have attempted to curate global biodiversity in public databases for molecular purposes, but these efforts are far from complete (Geiger et al, ; Lee et al, ). Our study highlights the need to quickly expand molecular databases in order to allow the full use of molecular methods in accurate species assignments.…”

New evidence of cryptic speciation in the family Longidoridae (Nematoda: Dorylaimida)

“…However, species delimitation based only on morphological studies may be a difficult task given the inconspicuous or non‐existent (e.g., pseudocryptic and cryptic speciation) differences among closely related species (Lajus, Sukhikh, & Alekseev, 2015). This phenomenon has been described extensively in many taxa such as nematodes in both marine and terrestrial ecosystems (Lee et al., 2017; Oliveira, Decraemer, Moens, dos Santos, & Derycke, 2017; Palomares‐Rius, Cantalapiedra‐Navarrete, & Castillo, 2014). There are several reasons that can be used to explain cryptic speciation in nematodes, such as genetic mutations and ecological adaptations by geographic location or host range (Palomares‐Rius et al., 2014; Wellborn & Broughton, 2008).…”

“…This enormous acceleration in the identification of cryptic species suggests that traditional morphological techniques may be deficient for accurate species identification in some species groups (Bickford et al., 2007; Jörger & Schrödl, 2013). In fact, the application of molecular techniques to taxa delimitation has uncovered a remarkable number of unknown cryptic species and/or revealed species hidden under one species identity (Gutiérrez‐Gutiérrez, Palomares‐Rius, Cantalapiedra‐Navarrete, Landa, & Castillo, 2011; Lee et al., 2017; Palomares‐Rius et al., 2014; Pérez‐Portela, Arranz, Rius, & Turon, 2013; Pfenninger & Schwenk, 2007). The conserved morphology that characterizes soil nematodes has led to the development of molecular methods using different fragments of nuclear (nc) ribosomal and mitochondrial DNA (mt) gene sequences to be used in DNA barcoding (Hebert, Ratnasingham, & de Waard, 2003; Palomares‐Rius, Cantalapiedra‐Navarrete, Archidona‐Yuste, Blok, & Castillo, 2017; Palomares‐Rius, Cantalapiedra‐Navarrete, Archidona‐Yuste, Subbotin, & Castillo, 2017; Palomares‐Rius et al., 2014).…”

“…Deciphering the cryptic biodiversity of soil nematodes is an essential task to increase our knowledge about soil ecosystem functioning (Barnes et al., 2018). Many cryptic species of both free‐living and plant‐parasitic nematodes (PPNs) have been discovered (Lee et al., 2017; Palomares‐Rius et al., 2014). In the case of PPNs, the discovery and unraveling of cryptic species has implications in food security, quarantine, and agronomic management of crops (Palomares‐Rius et al., 2014).…”