Genetic connectivity from the Arctic to the Antarctic: Sclerolinum contortum and Nicomache lokii (Annelida) are both widespread in reducing environments

Abstract

The paradigm of large geographic ranges in the deep sea has been challenged by genetic studies, which often reveal putatively widespread species to be several taxa with more restricted ranges. Recently, a phylogeographic study revealed that the tubeworm Sclerolinum contortum (Siboglinidae) inhabits vents and seeps from the Arctic to the Antarctic. Here, we further test the conspecificity of the same populations of S. contortum with additional mitochondrial and nuclear markers. We also investigate the genetic connectivity of another species with putatively the same wide geographic range - Nicomache lokii (Maldanidae). Our results support the present range of S. contortum, and the range of N. lokii is extended from vents and seeps in the Nordic Seas to mud volcanoes in the Barbados Trench and Antarctic vents. Sclerolinum contortum shows more pronounced geographic structure than N. lokii, but whether this is due to different dispersal capacities or reflects the geographic isolation of the sampled localities is unclear. Two distinct mitochondrial lineages of N. lokii are present in the Antarctic, which may result from two independent colonization events. The environmental conditions inhabited by the two species and implications for their distinct habitat preference is discussed.

Figure 1

Map of sampling stations for Sclerolinum contortum and Nicomache lokii generated in QGIS. The two stations in the Barbados Trench were located so close together that these are indicated with only one circle. There were also multiple sampling stations on the E2 ridge in the eastern Scotia Sea (see Table 1).

Figure 2

TCS haplotype networks of COI, 16S, CytB and 28S of Sclerolinum contortum and Nicomache lokii Each line represents one mutation, and black dots represents missing haplotypes. The size of the circles is proportional to the sample size of the haplotype, and haplotype designation and sample size (in brackets) is also indicated for each haplotype. For 28S two sequences were included per specimen, but the size of the circles is scaled to represent number of specimens, and the number in brackets is also scaled in the same way (number of sequences divided by two). Haplotypes are colored according to location, and corresponds to the colors in Fig. 1: Loki’s Castle – light green, HMMV – dark green, GoM – light blue, Barbados Trench – dark blue, Hook Ridge – orange, eastern Scotia Sea – yellow. For Nicomache lokii, haplogroup A is highlighted with a red outline.

Figure 3

Species tree of Nicomache spp. with Petaloproctus tenuis as outgroup. Node values represent posterior probabilities and node heights are median heights. The phylogeny was inferred under the multispecies coalescent model in BEAST2 using the STACEY package for species delimitation, and with the tree models for 28S and 18S linked.