Population structure and phylogenetic relationships of a new shallow‐water Antarctic phyllodocid annelid

Abstract

Shallow‐water polychaetes are abundant and diverse components of the Southern Ocean benthic communities, and although they have been widely studied, new species that are relatively common are still discovered. Here, we report the discovery of Pterocirrus giribeti sp. n., a new and abundant intertidal and upper‐subtidal Antarctic phyllodocid. To establish the phylogenetic relationships of the new species, we sequenced two nuclear (18S and 28S) and two mitochondrial (COI and 16S) markers. Although the phylogenetic relationships obtained for the family Phyllodocidae were not fully resolved, we assigned our new phyllodocid to the genus Pterocirrus based on both its phylogenetic position and its morphological characters. Using COI and 16S sequences of 126 and 118 individuals, respectively, from eight populations across the South Shetland Islands and the Antarctic Peninsula, we also investigated the genetic diversity and gene flow patterns of this new species. Our results suggested that all populations were panmictic, likely due to the presence of planktotrophic larvae allowing long‐distance dispersal. Interestingly, some genetic substructure was detected despite panmixis, and we identified a semipermeable barrier coinciding with an oceanic front produced by the intrusion into the Bransfield Strait of a tongue of water from the Weddell Sea. This front produced signatures of differentiation on populations at the tip of the West Antarctic Peninsula. Moreover, our results indicated a recent demographic expansion throughout the sampled area, in agreement with the “glacial refugium” hypothesis stated for other Antarctic shallow‐water invertebrates.

Population substructure and signals of divergent adaptive selection despite admixture in the sponge Dendrilla antarctica from shallow waters surrounding the Antarctic Peninsula

“…These results support the existence of a recent and rapid demographic expansion of D. antarctica in the WAP and the South Shetlands, which could have started after the last glacial-interglacial alternation (~20,000-10,000 years ago) when the last Antarctic shelf recolonization took place (see Allcock & Strugnell, 2012). This hypothesis has been suggested for other shallow-water Antarctic invertebrates (Díaz, Féral, Féral, David, Saucède, & Poulin, 2011;González-Wevar et al, 2011;Leiva, Riesgo, Riesgo, Avila, Rouse, & Taboada, 2018;Thornhill, Mahon, Norenburg, & Halanych, 2008), which could have migrated northwards to sub-Antarctic islands during glacial periods and recolonized the Antarctic shelf during interglacial periods.…”

“…Accordingly, the main genetic break we detected partially coincided with the Peninsula Front, but grouping King George Island together with O'Higgins Bay (Figure d), which is in agreement with the high migration flow from O'Higgins Bay to King George Island discussed above. A similar genetic break coincident with the Peninsula Front has already been identified for the brittle star O. victoriae using SNPs (Galaska et al, ), and also for the intertidal phyllodocid P. giribeti using a fragment of the mitochondrial COI marker (Leiva et al, ). In addition, different reproductive timing due to, for instance, the effects of north–south differences in sea‐ice retreat (Stammerjohn, Martinson, Smith, & Iannuzzi, ) could also play a role in population substructure with distinct breeding groups (Sugg, Chesser, Dobson, & Hoogland, ).…”

“…However, although this long-distance connectivity is unusual in sponges, it is common in other Antarctic marine invertebrates. Examples of high gene flow are shown in many Antarctic species, such as the brittle stars A. agassizii (Galaska et al, 2017a) and Ophionotus victoriae (Galaska et al, 2017b), the Antarctic limpet N. concinna (González-Wevar et al, 2013), the nemertean Parborlasia corrugatus (Thornhill et al, 2008) and the annelid Pterocirrus giribeti (Leiva et al, 2018).…”

“…Despite the lack of strong population structure, DAPC detected O. victoriae using SNPs (Galaska et al, 2017a), and also for the intertidal phyllodocid P. giribeti using a fragment of the mitochondrial COI marker (Leiva et al, 2018). In addition, different reproductive timing due to, for instance, the effects of north-south differences in sea-ice retreat (Stammerjohn, Martinson, Smith, & Iannuzzi, 2008) could also play a role in population substructure with distinct breeding groups (Sugg, Chesser, Dobson, & Hoogland, 1996).…”

Detecting glacial refugia in the Southern Ocean

“…However, the data analysis and/or interpretation of preliminary evidence were constrained by various factors, leaving the refugia hypotheses unanswered. Some studies suggested that evidence of glacial survival is reflected by overall genetic patterns but did not propose explicit locations of glacial refugia (Raupach et al 2010, Dömel et al 2015, Sromek et al 2015, Leiva et al 2018, Miller et al 2018), while others had limited sample coverage (Janko et al 2007, Baird et al 2012, Díaz et al 2012, Wiernes et al 2013) and were confounded by discoveries of multiple cryptic species in datasets (Wilson et al 2009, Allcock et al 2011, Baird et al 2011, Wiernes et al 2013, Harder et al 2016, González‐Wevar et al 2019).…”