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

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The importance of coastal morphology, and its influence on the magnitude of larval delivery and subsequent recruitment patterns of brachyuran decapods, was investigated at a broad range of spatial and temporal scales along the central coast of Chile. Larvae were quantified through plankton net towing as well as by using artificial settlement collectors deployed at different depths, while the abundance of benthic stages was quantified via in situ SCUBA airlifting and visual surveys. The abundance of young-of-the-year (YOY) and of individuals older than 1 yr (>1 yr) was compared between sites with contrasting conditions of coastal exposure at peninsulas several hundred kilometers apart. Additionally, we pursued a temporally more detailed surveying program, which included more species, at the southernmost peninsula. From our results we conclude that: (1) in general, the abundance of Paraxanthus barbiger, the most abundant species throughout, was greater at all locations in 2003 compared with 2004 and it was also greater (particularly >1 yr individuals) at protected sites; (2) for most of the species, the abundance of megalopae and YOY was highly seasonal, with peaks during the austral spring and summer months; and (3) for at least 2 of the 4 species considered in the southernmost peninsula, the abundance of YOY and >1 yr individuals exhibited higher abundance at the protected site. In spite of our efforts, we failed to find significant correlation between local abundance of settlers on artificial collectors and YOY individuals that settled in nursery habitats directly below. Post-settlement mortality, operating very soon after settlement, is a likely explanation for this finding. Our study highlights the importance of considering factors such as coastal morphology together with the occurrence of post-settlement processes when studying coastal organisms with complex life cycles.

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BackgroundDespite the impressive growth of sequence databases, the limited availability of nuclear markers that are sufficiently polymorphic for population genetics and phylogeography and applicable across various phyla restricts many potential studies, particularly in non-model organisms. Numerous introns have invariant positions among kingdoms, providing a potential source for such markers. Unfortunately, most of the few known EPIC (Exon Primed Intron Crossing) loci are restricted to vertebrates or belong to multigenic families.ResultsIn order to develop markers with broad applicability, we designed a bioinformatic approach aimed at avoiding multigenic families while identifying intron positions conserved across metazoan phyla. We developed a program facilitating the identification of EPIC loci which allowed slight variation in intron position. From the Homolens databases we selected 29 gene families which contained 52 promising introns for which we designed 93 primer pairs. PCR tests were performed on several ascidians, echinoderms, bivalves and cnidarians. On average, 24 different introns per genus were amplified in bilaterians. Remarkably, five of the introns successfully amplified in all of the metazoan genera tested (a dozen genera, including cnidarians). The influence of several factors on amplification success was investigated. Success rate was not related to the phylogenetic relatedness of a taxon to the groups that most influenced primer design, showing that these EPIC markers are extremely conserved in animals.ConclusionsOur new method now makes it possible to (i) rapidly isolate a set of EPIC markers for any phylum, even outside the animal kingdom, and thus, (ii) compare genetic diversity at potentially homologous polymorphic loci between divergent taxa.

One of the most relevant characteristics of the extant Southern Ocean fauna is its resiliency to survive glacial processes of the Quaternary. These climatic events produced catastrophic habitat reductions and forced some marine benthic species to move, adapt or go extinct. The marine benthic species inhabiting the Antarctic upper continental shelf faced the Quaternary glaciations with different strategies that drastically modified population sizes and thus affected the amount and distribution of intraspecific genetic variation. Here we present new genetic information for the most conspicuous regular sea urchin of the Antarctic continental shelf, Sterechinus neumayeri. We studied the patterns of genetic diversity and structure in this broadcast-spawner across three Antarctic regions: Antarctic Peninsula, the Weddell Sea and Adélie Land in East Antarctica. Genetic analyses based on mitochondrial and nuclear markers suggested that S. neumayeri is a single genetic unit around the Antarctic continent. The species is characterized by low levels of genetic diversity and exhibits a typical star-like haplotype genealogy that supports the hypothesis of a single in situ refugium. Based on two mutation rates standardized for this genus, the Bayesian Skyline plot analyses detected a rapid demographic expansion after the Last Glacial Maximum. We propose a scenario of rapid postglacial expansion and recolonization of Antarctic shallow areas from a less ice-impacted refugium where the species survived the LGM. Considering the patterns of genetic diversity and structure recorded in the species, this refugium was probably located in East Antarctica.

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endemic to South Georgia), M. steineni (South Georgia and Crozet Island) and the morphologically variable M. violacea (=M. expansa , M. porcellana and M. pruinosa) , with populations in southern South America , the Falkland/Malvinas , Crozet and Kerguelen Islands. Margarella violacea and M. achilles are sister species, closely related to M. steineni, with M. antarctica sister to all these. This taxonomy reflects contrasting biogeographic patterns on either side of the APF in the Southern Ocean. Pop-ulations of Margarella north of the APF (M. violacea) showed significant genetic variation but with many shared haplotypes between geographically distant populations. By contrast, populations south of the APF (M. antarctica, M. steineni and M. achilles) exhibited fewer haplotypes and comprised three distinct species, each occurring across a separate geographical range. We hypothesize that the biogeographical differences may be the consequence of the presence north of the APF of buoyant kelpspotential longdistance dispersal vectors for these vetigastro-pods with benthic-protected developmentand their near-absence to the south. Finally, we suggest that the low levels of genetic diversity within higher-latitude Margarella reflect the impact of Quaternary glacial cycles that exterminated local populations during their maxima.