When scientists from HMS Challenger dredged animals from over 5km depth, they finally laid to rest the azoic hypothesis of Edward Forbes, that life could not exist in cold dark depths of theocean, and thereby opened the doors to true deep-sea biology. The past decade has witnessed a furthersea change in our view of marine diversity, if I may be permitted the pun, a change driven to a largeextent by improved knowledge from Antarctica. For many years we viewed the tropics as the enginesof diversity; species arose in warm clear seas, especially those associated with coral reefs, and spreadslowly to populate the harsher high latitudes. Early studies of the isopod fauna had also suggested thatat least some organisms living on the continental shelf of Antarctica may have originated in the deepsea. After a period of intense work, much of it under the auspices of the SCAR EASIZ (Ecology of theAntarctic Sea Ice Zone) and more recently the EVOLANTA(Evolution in Antarctica) programmes, wecan now modify both hypotheses, with powerful implications for our understanding of global marinediversity. The marine invertebrate fauna of the Antarctic continental shelf is now better described thanmight be thought, and the total fauna may well exceed 17000 taxa. Interestingly, there are very fewplaces in the world with comparable data, but we can say that the fauna has had a long history ofevolution in situ and is not simply a last refuge for taxa that originated elsewhere.

Abundance, diversity, and distribution of suprabenthic Isopoda caught from a water layer between 0.27 to 0.60 m above the seafloor were analysed. The samples were taken during the ANT XV/3 cruise on RV Polarstern by means of an epibenthic sledge along two transects in the southern Weddell Sea (Vestkapp and Halley Bay) and another one east of King George Island. At each of these three bathymetric transects, five to six stations were sampled between 200 and 2000 m. In total, 4258 specimens of isopods were sampled at 14 stations standardized to 1000 m2 hauls. 114 species were identified from 49 genera and 23 higher taxa (families and suborders) of Isopoda. Most of them belonged to the suborder Asellota. Dominant families are Munnopsididae (Eurycopinae, Ilyarachninae), Joeropsidae, Munnidae, Paramunnidae, Ischnomesidae and Desmosomatidae. No striking differences were found between areas (Vestkapp, Halley Bay, Kapp Norvegia, and Bransfield Strait). Overall isopod abundances were highest at the shallowest station; species richness was slightly higher above 1000 m depth.

Based on data from the Weddell Sea in the Atlantic sector of the Southern Ocean, the total number of macrozoobenthic species was estimated for the entire Antarctic shelf using species-accumulation methods, jack-knife estimators, and Incidence-based Coverage Estimators of species richness. Ranging between 11 000 and 17 000 expected species, Antarctica seems to have an intermediate species richness when compared to other selected tropical, temperate or Arctic habitats.

The jaw musculature of notothenioid fishes is described and compared based on a total of 38 species referred to eight families of the suborder Notothenioidei. In the Notothenioidei, the adductor mandibulae, the largest and most conspicuous of the cranial muscles, is generally composed of sections A1, A2, A3 and Aw as in the generalized percoids. The morphology of the adductor mandibulae is similar in most notothenioid families except the Nototheniidae and Bathydraconidae. Notothenia, Paranotothenia and Dissostichus are clearly distinguished from the other nototheniid genera in having A3. Gymnodraco of the Bathydraconidae has a fused A1-A2 complex and the anterior element is segmented by a tendinous intersection from the A1-A2 complex. These features are unique to Gymnodraco and not seen in other bathydraconids. The Harpagiferidae and Artedidraconidae share the same apomorphy, the presence of A1β, with the Nototheniidae and have no synapomorphies with the Bathydraconidae and Channichthyidae. The character distribution, however, shows some inconsistencies with the previous classifications. Based on the limited evidence obtained in this study, the Notothenioidei can be divided into six groups and it seems reasonable to suggest a review of the current classification of the Nototheniidae.

In the Antarctic ciliate, Euplotes focardii, the heat-shock protein 70 (Hsp70) gene does not show any appreciable activation by a thermal stress. Yet, it is activated to appreciable transcriptional levels by oxidative and chemical stresses, thus implying that it evolved a mechanism of selective, stress-specific response. A basic step in investigating this mechanism is the determination of the complete nucleotide sequence of the E. focardii Hsp70 gene. This gene contains a coding region specific for an Hsp70 protein that carries unique amino acid substitutions of potential significance for cold adaptation, and a 5' regulatory region that includes sequence motifs denoting two distinct types of stress-inducible promoters, known as “Heat Shock Elements” (HSE) and “Stress Response Elements” (StRE). From the study of the interactions of these regulatory elements with their specific transactivator factors we expect to shed light on the adaptive modifications that prevent the Hsp70 gene of E. focardii from responding to thermal stress while being responsive to other stresses.

Sterechinus neumayeri is an abundant regular sea urchin that lives in the shallow Antarctic waters. This organism has been used as a model system in many fields of the Antarctic biology. Yet, understanding of the evolutionary identity of the species, such as its phylogenetic relationships and divergence time, remains limited. Here, we reconstructed the molecular phylogenies of the species together with two sea urchin species in southernmost South America (Loxechinus albus and Pseudechinus magellanicus), a parechinid species (Paracentrotus lividus) and three strongylocentrotid species (Strongylocentrotus purpuratus, S. intermedius, and Hemicentrotus pulcherrimus) using mitochondrial DNA sequences of 12S rDNA-tRNA(gln) region (877nt) and cytochrome oxidase subunit I (COI, 1079nt). The rate of sequence evolution and the divergence time of the species were then estimated from the trees. The phylogenetic trees reveal that S. neumayeri is a sister group to the lineage of L. albus and P. lividus, and separated from the lineage 24–35 million years ago (m.y.a.). The divergence between S. neumayeri and L. albus coincides with the separation of Antarctica from South America, suggesting that the tectonic event must have provoked the cladogenesis of the species through vicariance.

Hypotheses concerning the diversification of notothenioid fishes have relied extensively on estimates of divergence times using molecular clock methods. The timing of diversification of the cold adapted antifreeze glycoprotein (AFGP)-bearing Antarctic notothenioid clade in the middle to late Miocene has been correlated with the onset of polar climatic conditions along the Antarctic Continental Shelf. Critical examination of the previous molecular clock analyses of notothenioids reveals several problems associated with heterogeneity of nucleotide substitution rates among lineages, the application of potentially inappropriate nucleotide substitution rates, and the lack of confidence intervals for divergence time estimates. In this study, the notothenioid partial gene mtDNA 12S-16S rRNA (PG-rRNA) molecular clock was reanalysed using a tree-based maximum likelihood strategy that attempts to account for rate heterogeneity of nucleotide substitution rates among lineages using the penalized likelihood method, and bootstrap resampling to estimate confidence intervals of divergence time estimates. The molecular clock was calibrated using the notothenioid fossil Proeleginops grandeastmanorum. Divergence time estimates for all nodes in the PG-rRNA maximum likelihood tree were substantially older than previous estimates. In particular, the estimated age of the AFGP-bearing Antarctic notothenioid clade predates the onset of extensive sea ice and development of polar conditions by at least 10 million years. Despite caveats involving the fossil calibration and limitations of the PG-rRNA dataset, these divergence time estimates provide initial observations for the development of a novel model of the diversification of cold adapted Antarctic notothenioid fishes.

To study how teleosts have modified their immunoglobulin structures to adapt to the Antarctic environment, we investigated Trematomus bernacchii IgM at protein and gene levels. Serum IgM was purified, characterized and quantified. The nucleotide and deduced amino acid sequences of IgL and IgH were determined. Upon comparison with other teleosts, T. bernacchii IgH showed a higher hydrophilic character and the presence of two remarkable insertions, probably increasing the flexibility of the molecule. To investigate the amplitude of the antibody repertoire, a VH library was constructed. The analysis of rearranged VH/D/JH transcripts revealed a high occurrence of the RGYW motif and a clear bias in the usage of serine codons. Diversity generated by insertions/deletions occurred more often than in other species. VH sequences fell into only two gene families referred to as Trbe VH I and Trbe VH II. The deduced amino acid sequence of the membrane region was found to be the longest and an F/Y substitution was observed at a highly conserved position. Models of the transmembrane helices of T. bernacchii and other teleost Ig were constructed by molecular dynamics. Finally, the analysis of the antibody specificity revealed the presence of antibodies specific to the proteins of nematode parasites.

The non-long terminal repeat retrotransposons Rex1 and Rex3 were identified in 13 species of Antarctic fishes from five families of the suborder Notothenioidei. Partial reverse transcriptase gene sequences were characterized for Notothenia coriiceps, Trematomus newnesi and Dissostichus mawsoni (Nototheniidae), and Gymnodraco acuticeps (Bathydraconidae). Rex1 and Rex3 both formed a notothenioid-specific monophyletic group compared to the corresponding elements from other fishes. They globally evolved under purifying selection, showing their activity during notothenioid evolution. Fluorescence in situ hybridization analysis of the chromosomal distribution of Rex1 and Rex3 was performed for several notothenioid fish species. Rex1 was generally less abundant than Rex3, which was widely scattered on the chromosomes with more intense hybridization patterns in some specific zones. Particularly, Rex3 accumulated in Chionodraco hamatus in pericentromeric areas, short arms of some pairs as well as in an intercalary band in the long arm of the Y chromosome similarly to a previously described DNA transposon. Such pattern similarities suggest the presence of autosomal and gonosomal regions of preferential accumulation for different types of repeated elements in notothenioid genomes. To the best of our knowledge, this report is the first description and analysis of retrotransposable elements in Antarctic fish genomes.

Organisms living in the Arctic and Antarctic are exposed to strong environmental constraints, especially temperature. Consequently, haemoglobin evolution has included adaptations with implications at the biochemical, physiological and molecular levels. The northern and southern polar oceans have very different oceanographic characteristics. Within the study of the molecular bases of cold adaptation in fish inhabiting polar habitats, and taking advantage of the information available on haemoglobin structure and function, we analysed the evolutionary history of the α and β globins of Antarctic and Arctic haemoglobins, under the assumption of the molecular-clock hypothesis, as a basis for reconstructing the phylogenetic relationships between species. Temperate fish, including two non-Antarctic notothenioids of special evolutionary interest, were also considered. Phylogenetic analysis was performed on the multiple sequence alignments constructed with the programme Clustal X. Tree topologies indicate that the chains of Antarctic major and minor haemoglobins cluster in two well separated groups and diverged prior to cold adaptation, forming a monophyletic group. In Arctic haemoglobins, the structure/function relationship reveals important differences in comparison with Antarctic ones, indicating a distinct evolutionary pathway. The Arctic ichthyofauna (unlike the Antarctic, dominated by one taxonomically uniform group) is characterized by high diversity, reflected in the phylogeny of a given trait. The constant physico-chemical conditions of the Antarctic waters are matched by a clear grouping of fish globin sequences, whereas the variability typical of the Arctic Ocean corresponds to high sequence variation, reflected in the trees by scattered intermediate positions between the Antarctic and non-Antarctic clades. The evolutionary history of the Root effect, an important physiological feature of fish haemoglobin, was investigated. Analysis of the fate of the residues of the β chains suggested to be correlated with the Root effect indicate that they should rather be regarded as ancestral characters, inherited by some species but not by others.

Ninety-five percent of the fish species known from the Antarctic continental shelf and upper slope are acanthomorphs, i.e. spiny teleosteans. Notothenioids (suborder Notothenioidei) are acanthomorphs and so is their sister group. Unfortunately, until recently acanthomorph intra-relationships were so poorly known that it was necessary to sample all of this diversity just to search for a single sister group relationship. Using recent advances in acanthomorph molecular phylogenetics, particular properties of separate analyses and a new protocol of dataset combination, we identified a clade that contains the sister group of notothenioids, the Percidae (perches), and a number of relatives. Among these relatives are the Serranidae (sea basses), the genera Trachinus (weeverfish), Chelidonichthys (gurnard), Scorpaena (scorpionfish), and a group composed of the Zoarcoidei (eelpouts) and the Cottoidei (sculpins) with the Gasterosteidae (sticklebacks) as their sister group. Interestingly, that clade contains 88% of the fish species found on the Antarctic continental shelf and upper slope. The interrelationships of its components and their distribution show that the Antarctic benthic fish fauna has at least three origins.