Evolutionary pathways among shallow and deep-sea echinoids of the genus Sterechinus in the Southern Ocean

Abstract

Artículo de publicación ISIAntarctica is structured by a narrow and deep continental shelf that sustains a remarkable number of benthic species. The origin of these species and their affinities with the deep-sea fauna that borders the continent shelf are not clear. To date, two main hypotheses have been considered to account for the evolutionary connection between the faunas: (1) either shallow taxa moved down to deep waters (submergence) or (2) deep-sea taxa colonized the continental shelf (emergence). The regular sea urchin genus Sterechinus is a good model to explore the evolutionary relationships among these faunas because its five nominal species include Antarctic and Subantarctic distributions and different bathymetric ranges. Phylogenetic relationships and divergence times among Sterechinus species were established using the COI mitochondrial gene by assuming a molecular clock hypothesis. The results showed the existence of two genetically distinct main groups. The first corresponds exclusively to the shallow-water Antarctic species S. neumayeri, while the second includes all the other nominal species, either deep or shallow. Antarctic or Subantarctic. Within the latter group, S. dentifer specimens all formed a monophyletic cluster, slightly divergent from all other specimens, which were mixed in a second cluster that included S. agassizi from the continental shelf of Argentina, S. diadema from the Kerguelen Plateau and S. antarcticus from the deep Antarctic shelf. These results suggest that the deeper-water species S. dentifer and S. antarcticus are more closely related to Subantarctic species than to the shallow Antarctic species S. neumayeri. Thus, for this genus, neither the submergence nor emergence scenario explains the relationships between Antarctic and deep-sea benthos. At least in the Weddell quadrant, the observed genetic pattern suggests an initial separation between Antarctic and Subantarctic shallow species, and a much later colonization of deep water from the Subantarctic region, probably promoted by the geomorphology of the Scotia Arc.This studywassupportedbytheGrantsINACHD05-09,Conicyt Ph.D. GrantnoD-21080136toA.D.,andbytheprojectsP05-002 ICM andPFB023(InstituteofEcologyandBiodiversity,Universidad de Chile)andINACH02-02,13-05andECOSC06B02toE.PandA.D; ANR AntflocksforB.D.,J.P.F.andT.S.Mostofthesampleswere collected duringAntarcticexpeditionsthroughtheIPEV(formerly IFRTP) programno195BENTHOS-MACandprogramno345 BENTHADEL, PolarsternAntarktisXXIII/8;CEAMARC,Bentart’06. Thanks arealsoduetointernationalprogramsCAML,EBA-SCAR and PROSUL-BrazilforencouragingandsupportingAntarctic research inEvolution

Patrones de diversidad y estructura genética en especies antárticas y subantárticas de Nacella (Nacellidae)

“…En Subantártica, la marcada diferenciación entre los linajes de Patagonia e Isla Kerguelén contrastan con los resultados registrados en otros invertebrados que muestran altos niveles de conectividad entre provincias geográficamente alejadas. Distintos grupos de invertebrados incluyendo mitílidos (Gérard et al 2008), crustáceos (Nikula et al 2010), equinodermos (Díaz et al 2011) y gasterópodos pulmonados (Cumming et al 2014) muestran evidencia de conectividad contemporánea entre provincias subantárticas geográficamente alejadas. De esta forma, para Nacella la distancia geográfica, los patrones oceanográficos y rasgos de historia de vida como su modo de desarrollo representan una barrera infranqueable para la conectividad a lo largo de Subantártica (González-Wevar et al 2010).…”

“…Estos resultados permiten corroborar el impacto generado por los ciclos glaciales del Cuaternario sobre los patrones de diversidad y estructura genética en Antártica y Subantártica. Bajos niveles de diversidad como los registrados en la lapa antártica han sido registrados en otros invertebrados de la región incluyendo Chorismus antarcticus (Pfeffer, 1887) (Raupach et al 2010), Parborlasia corrugatus (McIntosh, 1876) (Thornhill et al 2008) y Sterechinus neumayeri (Meissner, 1900) (Díaz et al 2011). Como se esperaba dentro de un contexto latitudinal, los niveles de diversidad genética en N. concinna de Antártica fueron menores que los registrados en sus parientes subantárticos N. magellanica (Patagonia) y N. edgari (Isla Kerguelén), lo que sugiere un efecto demográfico más pronunciado de las glaciaciones a medida que aumenta la latitud.…”

“…Por un lado, la CCA actúa como una gran barrera para la mayoría de los invertebrados marinos entre provincias antárticas y subantárticas (Shaw et al 2004;Page & Linse, 2002;Griffiths et al 2009;González-Wevar et al 2012a;Poulin et al 2014). Por otro lado, a lo largo de Subantártica la CCA actúa como un importante medio de transporte entre provincias geográficamente distantes, especialmente para organismos con alta capacidad dispersiva (Gérard et al 2008;Waters, 2008;Fraser et al 2009;Díaz et al 2011) y para aquellos que viven asociados a macroalgas (Nikula et al 2010;Fraser et al 2011;Cumming et al 2014). El segundo periodo durante el Mioceno medio (~ 14 Ma) se asocia a un incremento en la formación de aguas de profundidad en el OA, la intensificación de CCA y al re-establecimiento de una capa de hielo permanente en Antártica Este y en el margen Pacífico de Península Antártica (Lawver & Gahagan, 2003;Verducci et al 2009).…”

Against the flow: evidence of multiple recent invasions of warmer continental shelf waters by a Southern Ocean brittle star

“…Such a deep sea link has been used to explain the close genetic connectivity between sub-Antarctic and Antarctic morphotypes of the echinoid Sterechinus (Díaz et al, 2011). The limits of adult O. lymani/carinifera dispersal are unknown.…”

A new member of the genus Antarctonemertes (Hoplonemertea, Nemertea) from Antarctic waters

“…4), a pattern indicative of bottleneck events followed by population expansion (Slatkin and Hudson 1991). Similar star-like haplotype networks were recovered for the Antarctic shallowwater common echinoid Sterechinus neumayeri (Meissner, 1900) from both the Antarctic Peninsula and Terra Adélie (East Antarctica) (Díaz et al 2011). Furthermore, the common heteronemertean Parborlasia corrugatus and the deepwater shrimps Chorismus antarcticus (Pfeffer, 1887) and Nematocarcinus lanceopes Spence Bate, 1888 also displayed similar star-like haplotype networks, although several populations across the Southern Ocean were studied together for these three species (Thornhill et al 2008;Raupach et al 2010).…”