Is ‘everything everywhere’? Unprecedented cryptic diversity in the cosmopolitan flatworm Gyratrix hermaphroditus

Abstract

Many nominal species of microscopic animals traditionally fitting the ‘everything is everywhere’ paradigm have been revealed to be complexes of cryptic species. Here, we explore species diversity within the micrometazoan flatworm Gyratrix hermaphroditus—unique among meiofauna because of its global occurrence in a wide variety of brackish, freshwater and marine environments. With maximum likelihood and Bayesian approaches, we analysed 18S, 28S, 5.8S and ITS2 rDNA sequences from 401 specimens across the global distribution of G. hermaphroditus. Generalized Mixed Yule Coalescent (GMYC) and Automatic Barcode Gap Discovery (ABGD) methods delineated 78 and 62 putative species, respectively. This renders G. hermaphroditus one of the most species‐rich complexes known to date. Based on shape variations of the male copulatory organ, 14 morphotypes corresponding with molecular clades were identified within the species complex. Within morphotypes, morphometric measurements were able to further discriminate between GMYC species using discriminant analyses. While most putative species occur on local or regional scales, over 10% are distributed over vast distances (>500 km apart) and two GMYC and six ABGD species have colonised multiple continents. This suggests that the cosmopolitanism of the G. hermaphroditus species complex is not just caused by mixing cryptic species with a more limited geographic distribution, but is due to the presence of previously unrecognised cosmopolitan taxa. The wide variation in distribution patterns between putative species indicates that meiofaunal biogeography should not be simplified into ‘everything is everywhere’, but rather entails every ecological state, extending from local endemism to true cosmopolitanism.

Late Cenozoic environmental changes drove the diversification of a weevil genus endemic to the Cape Floristic Region

“…This method collapses sequences into haplotypes and then constructs statistical parsimony haplotype networks formed at the 95% confidence level. This SD approach was carried out only on the concatenated dataset (following other authors; see e.g ., Vondráček et al, 2018, Tessens et al, 2021), considering each network as a putative species. As a sixth SD approach, we used a multilocus coalescent‐based SD approach implemented in the program tr2 (Fujisawa et al, 2016).…”

Cryptic, sibling or neither of the two? Integrative species delimitation ofPsylliodesflea beetles with overlapping ranges

“…Moreover, this study substantiates the relevance of a range‐wide assessment of morphological and genetic variation, including populations from the type locality, the entire overlapping area between the species, as well as allopatric populations of both species. Such an exhaustive sampling makes it less likely the presence of well‐known artefacts derived from a partial analysis of genetic and morphological variability (Bergsten et al, 2012; Furfaro et al, 2021; Meyer & Paulay, 2005; Phillips et al, 2019; Puillandre et al, 2012; Tessens et al, 2021).…”

“…In other cases, characters used for the species diagnosis and assumed to have a discrete variation, when further assessed across a wider geographic and population scope, reveal a pattern of continuous variation that is overlapping with closely related species. This is especially likely for wide‐ranging species whose descriptions are based on a few individuals from a low number of localities covering a limited portion of the species range (Tessens et al, 2021). This is not an infrequent case for species described in the old times or from poorly sampled areas (Darwell & Cook, 2017; Deng et al, 2019; McBride et al, 2009; Morek et al, 2019).…”

Species composition and abundance of free-living turbellarians in three different wetlands in Southern Brazil

“…This uncertainty could generate misinterpretations in determining the abundance and diversity of turbellarians at different sites. Thus, analyses using (meta) barcoding as an additional identification tool are highly recommended for ecological and biodiversity studies that would help us to detect sibling species that would otherwise be difficult to identify (Balsamo et al 2020, Tessens et al 2021. The present analysis of the turbellarian community on floating vegetation microhabitats provides an overview that is useful in understanding the dynamics of ecological systems in wetlands in southern Brazil, particularly inside the ESEC Taim nature reserve.…”