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6 August 2024 Panmixia and local endemism: a revision of the Eubranchus rupium species complex with a description of new species
Darya Y. Grishina, Dimitry M. Schepetov, Tatiana I. Antokhina, Manuel António E. Malaquias, Ángel Valdés, Irina A. Ekimova
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Abstract

Species of the genus Eubranchus Forbes, 1838 (Mollusca: Gastropoda: Nudibranchia) are common faunistic elements of boreal benthic ecosystems, associated with hydroid communities. Recent studies have suggested that the widely distributed trans-Arctic E. rupium (Møller, 1842) constitutes a complex of at least three candidate species, but the detailed taxonomy of the complex remains unresolved. The purpose of the present paper is to conduct an integrative taxonomic study including molecular genetic methods (a phylogenetic analysis using COI, 16S rRNA and histone H3 with application of species delimitation methods) and morphological study (light and scanning electron microscopy) of E. rupium and closely related species. The specific aims of this study were to establish the species boundaries, morphological variability, and the phylogeographic structure within this group. The phylogeographic analysis included a TCS-based network analysis, an analysis of molecular variance (AMOVA), divergence time estimations, and ancestral area reconstructions. We demonstrate that specimens initially identified as E. rupium included three distinctive species: the nominal E. rupium with an amphiboreal range, the new species Eubranchus novik sp. nov. from the Sea of Japan, for which a taxonomic description is provided in this paper, and Eubranchus sp. from the northern Kuril Islands, which requires the collection and study of additional material for formal description. Our results confirm the amphiboreal distribution of E. rupium, as no geographic structure was found across Pacific, Arctic and Atlantic populations, and the results of the AMOVA analysis showed no differences between groups of samples from different geographic regions. The divergence of the ‘Eubrancus rupium species complex’ is estimated from the late Miocene or the Miocene–Pliocene boundary to the late Pliocene. It is hypothesised that the most probable ancestral region for the Eubranchus rupium species complex is the north-western Pacific, and the subsequent speciation likely occurred due to dispersal followed by allopatric speciation.

ZooBank: urn:lsid:zoobank.org:pub:228E0C46-0BF7-4DDD-9C00-67B50E298D65

Darya Y. Grishina, Dimitry M. Schepetov, Tatiana I. Antokhina, Manuel António E. Malaquias, Ángel Valdés, and Irina A. Ekimova "Panmixia and local endemism: a revision of the Eubranchus rupium species complex with a description of new species," Invertebrate Systematics 38(8), (6 August 2024). https://doi.org/10.1071/IS24032
Received: 4 April 2024; Accepted: 9 July 2024; Published: 6 August 2024
KEYWORDS
amphiboreal species
ancestral area reconstruction
biodiversity
Divergence time estimation
Mollusca
Nudibranch
phylogenetics
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