Molecular analysis of Arctic material of Dendronotus robustus and Dendronotus velifernext section
The present molecular analysis shows that there are two distinct species under the name Dendronotus robustus, corresponding to D. robustus Verrill, 1870 and D. velifer G.O. Sars, 1878. Of the sampled specimens, 11 belonged to the former species and five to the latter. Minimal uncorrected p-distances for the COI gene are significantly different between both species, with a range of 8.74% ±1.24%. Distances within D. robustus group are within 0.71%. Distances within D. velifer group are up to 0.54%, but distances between D. robustus and D. velifer groups reach 9.34%. Results obtained by PopART both for the COI and for 16S genes showed a network of haplotypes that clearly clustered into two groups coincident with the species D. robustus and D. velifer (Figure 4a, b).
Statistical analysis of the bathymetric distribution
The comparison of the bathymetric distribution of specimens of Dendronotus robustus and D. velifer which were involved in the molecular taxonomic analysis (see above) reveal significant statistical differences (p=0.002, Figure 4c). The bathymetric data for historical specimens of D. velifer and for recently collected D. robustus demonstrate statistically significant differences (p <0.001, Figure 4c; right lilac and left blue bars). At the same time, the bathymetric data between historical specimens of D. velifer and the recently collected specimens of D. velifer do not show any significant differences (Figure 4c).