Hidden diversity in two species complexes of munnopsid isopods (Crustacea) at the transition between the northernmost North Atlantic and the Nordic Seas

Abstract

Eurycope producta Sars, 1868 and Eurycope inermis Hansen, 1916 are two widely distributed and highly abundant isopod species complexes within Icelandic waters, a region known for its highly variable environment. The two species complexes have bathymetric depth ranges from 103 to 2029 m (E. producta) and from 302 to 2113 m (E. inermis). Molecular evidence was used for species delimitation within these species complexes by analyzing nuclear (18S rDNA, H3) and mitochondrial (16S rDNA, COI) sequence data. Tree-based methods (BI and ML) and four species delimitation methods (ABGD, GMYC, NDT, PTP) were applied, in order to disentangle the two species complexes. A total of eight and four species clades could be identified within samples of the E. producta and E. inermis complexes and respectively included the closely related species E. dahli Svavarsson, 1987; E. hanseni Ohlin, 1901; and E. cornuta Sars, 1864. The morphological findings coincide with the observed molecular species clades. The elucidated species clades were geographically and bathymetrically much more restricted than previously assumed. Eight species clades featured depth spans of less than 400 m and only four species clades featured depth spans of 1000 to 1500 m. Only two species clades (E. producta sensu stricto and E. inermis sensu stricto) were found on both sides of the Greenland-Scotland Ridge. Further, species distribution maps were generated using random forest, to predict potential distributional patterns for the resolved species clades of the two species complexes. We present the first attempt of combining morphological, molecular, and species distribution models in marine isopods thus far.