Lack of population genetic structure in the marine nematodes Ptycholaimellus pandispiculatus and Terschellingia longicaudata in beaches of the Persian Gulf, Iran

Abstract

We investigated genetic diversity and population genetic structure of two common benthic nematode species, Ptycholaimellus pandispiculatus and Terschellingia longicaudata, from sandy beaches in the area of Bandar Abbas (Iran), Persian Gulf. Based upon partial mitochondrial cytochrome oxidase c subunit 1 (COI) gene data, 17 and two haplotypes were found for P. pandispiculatus and Te. longicaudata, respectively. Analysis of molecular variance did not reveal a significant population genetic structure for either species. The absence of genetic structuring indicates substantial dispersal and gene flow in our study area. To assess the species structure of Te. longicaudata at a larger geographic scale, we compared 18S rDNA and COI sequences from Iran and the Scheldt Estuary in The Netherlands to ascertain whether they truly belong to the same species. Our data confirmed previous studies that Te. longicaudata likely constitutes a complex of multiple cryptic species, with one of these species having a (near) cosmopolitan distribution.

Metabarcoding data allow for reliable biomass estimates in the most abundant animals on earth

“…Those that could not be distinguished shared the same marker gene sequence and, as such, cannot be distinguished, based on sequencing (Table 2). The rRNA genes were recently suggested to be incapable of identifying many nematode taxa to species and genus level resolution was consequently suggested as a reliable lower-resolution alternative (Creer et al 2016;Sahraean et al 2017). It should, therefore, be considered in metabarcoding studies of unknown species composition, when the full species diversity is aimed at identification in a sample.…”

Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox

“…Of these, 40 papers reported an unchanged distribution of some of the focal taxa (accounting for 82 species), 25 reported an increase of distribution (including 112 species) and 22 a decrease of distribution (including 160 species). Only 27 papers used a combination of molecular and morphological data to assess species delineation (Todaro et al 1996(Todaro et al , 2014Curini-Galletti and Puccinelli 1998;Westheide and Hass-Cordes 2001;De Ley et al 2005;Sterrer and Sørensen 2006;Suatoni et al 2006;Leasi and Todaro 2007;Casu et al 2009;Neusser et al 2011;Eder et al 2011;Kieneke et al 2012;Jörger et al 2012; (Schmidt and Westheide 2000;Bhadury et al 2006;Todaro et al 2006;Casu and Curini-Galletti 2006;Bik et al 2010Bik et al , 2012Gruber-Vodicka et al 2011;Tulchinsky et al 2012;Baldrighi et al 2013;Yamasaki et al 2014;Fonseca et al 2014; Norenburg 2014, 2016;Meyer-Wachsmuth et al 2014;Scarpa et al 2015;Sahraean et al 2017). Moreover, 14 papers mentioned difficulties in morphological characterization of the considered taxa (we refer to this issue as the low-morphology problem, see below).…”

“…Considering the prevalence of cryptic species complexes and the subsequent reduction in distribution ranges in studies employing molecular investigations, the distribution of most meiofauna species seems clearly inflated as complexes of cryptic species consists of several, independent distributions, currently interpreted as a single distribution range(Casu and Curini-Galletti 2004;Derycke et al 2005;Andrade et al 2011;Tulchinsky et al 2012;Leasi and Norenburg 2014). Our survey showed that cosmopolitan or, at least, amphi-oceanic distributions of most meiofauna species seldom occur and that increases in distribution range are not supported by molecular approaches.Therefore, the taxonomic identity and assumed wide distribution ranges of many meiofauna species assumed to be examples of the 'meiofauna paradox' is not verified(Schmidt and Westheide 2000;Casu and Curini-Galletti 2006;Suatoni et al 2006;Casu et al 2009;Tulchinsky et al 2012;Jörger et al 2012;Kieneke et al 2012;Leasi et al 2013; Norenburg 2014, 2016;Meyer-Wachsmuth et al 2014;Karanovic et al 2016;Sahraean et al 2017;Kieneke and Nikoukar 2017). Careful reinvestigations, including detailed morphological and molecular analyses should resolve the paradox of widespread species.…”

A taxonomic review and revisions of Microstomidae (Platyhelminthes: Macrostomorpha)

“…Larsson et al 2008;Telford et al 2000;) and other meiofauna (e.g. Verheye et al 2016;Alvarez-Campos et al 2017;Kieneke & Nikoukar 2017;Michaloudi et al 2017;Sahraean et al 2017;Zhao et al 2018) and are thus applicable in identifying species and assessing intraspeciYic diversity.…”