Delimitation of cryptic species drastically reduces the geographical ranges of marine interstitial ghost-worms (Stygocapitella; Annelida, Sedentaria)

José Cerca,Christian Meyer,Günter Purschke,Torsten H Struck

doi:10.1016/j.ympev.2019.106663

José Cerca, Christian Meyer + Show 2 more

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https://doi.org/10.1016/j.ympev.2019.106663

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Abstract

The recognition of cryptic species concealed in traditionally established species may reveal new biogeographical patterns and alter the understanding of how biodiversity is geographically distributed. This is particularly relevant for marine ecosystems where the incidence of cryptic species is high and where species distribution data are often challenging to collect and interpret. Here, we studied specimens of the ‘cosmopolitan’ interstitial meiofaunal annelid Stygocapitella subterranea Knöllner, 1934 (Parergodrilidae, Orbiniida), obtaining data from four coastlines in the Northern hemisphere. Using phylogenetic tools and several species-delimitation methods (haplotype networks, GMYC, bPTP, maximum likelihood, posterior probability and morphology) we describe eight new Stygocapitella species. With one exception, all species are present along a single coastline, ultimately challenging the idea that Stygocapitella subterranea has a cosmopolitan distribution. We found evidence for several oceanic transitions having occurred in the past as well as a recent translocation, potentially due to human activity. No diagnostic characters were found, and qualitative and quantitative morphological data do not allow an unequivocal differentiation of the identified cryptic species. This suggests that (i) neither traditional diagnostic features nor quantitative morphology suffice to recognise species boundaries in cryptic species complexes, such as the Stygocapitella species complex; and that (ii) the recognition and description of cryptic species is of seminal importance for biodiversity assessments, biogeography and evolutionary biology.

Highlights

Species distribution data provide a valuable proxy to understand patterns of biodiversity occurrence across the globe, the influence of past geological events on taxa, and of human impact on biological communities (Holt et al, 2013)
This suggests that (i) neither traditional diagnostic features nor quantitative morphology suffice to recognise species boundaries in cryptic species complexes, such as the Stygocapitella species complex; and that (ii) the recognition and description of cryptic species is of seminal importance for biodiversity assessments, biogeography and evolutionary biology
Eight of the lineages in the tree are formally described as new species below, following species delimitation analyses, and for the sake of clarity we use their new species names (S. pacifica sp. nov., S. furcata sp. nov., S. berniei sp. nov., S. americae sp. nov., S. budaevae sp. nov., S. zecai sp. nov., S. josemariobrancoi sp. nov., and S. westheidei sp. nov.) as well as in Figs. 2 and 3

Summary

Introduction

Species distribution data provide a valuable proxy to understand patterns of biodiversity occurrence across the globe, the influence of past geological events on taxa, and of human impact on biological communities (Holt et al, 2013). Boundaries and biogeographic barriers are often hard to determine, and the patchiness of marine populations combined with the wide area occupied by oceans contributes to difficult sampling and collection. Species delimitation and identification are often compromised because organisms can be deformed following their collection and extraction from the water, due to preservation practices, or because they require sound taxonomic expertise, including adult features and unequivocal diagnostic characters (Cerca et al, 2018; Hellberg, 2009; Knowlton, 1993; Sterrer, 1973). Our understanding of evolutionary and ecological processes as well as biogeographic patterns in the sea is severely diminished (Hellberg, 2009; Johannesson, 1988; Knowlton, 1993)

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