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In the present work, persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and metabolites, polybrominated diphenyl ethers (PBDEs), and hexachlorocyclohexane (HCH) were analyzed in three Antarctic notothenioids fish species: Trematomus newnesi (TRN), Notothenia coriiceps (NOC) and Notothenia rossii (NOR). The contribution of each POP-family to the total load was as follows: ΣPCB (40%) > ΣDDT (27%) > ΣPBDEs (23%) > ΣHCH (10%). Among the 23 PCB congeners analyzed, penta -CBs homologues were the prevalent group, followed by hexa -CBs and hepta -CBs. DDT and its metabolites presented the following trend: p , p ′-DDT > p , p ′-DDE ~ p , p ′-DDD. PBDE profile was dominated by BDE-47 and BDE-99 congeners, followed by BDE-100 > BDE-28 > BDE-154, BDE-153. Among HCHs, the γ-HCH isomer was detected in all samples, constituting 69% total HCH load, while α-HCH and β-HCH contributions were 15% and 16%, respectively. The levels of POPs reported here suggest that NOR and NOC are more susceptible to accumulate the analyzed contaminants than TRN, a species not previously analyzed for POPs. Distribution of POPs among different tissues of the three species (muscle, liver, gonads, and gills) was also investigated. Considering lipid weight, the general pattern of POPs distribution in tissues indicated that while gonads showed higher levels of PCBs, DDTs and HCH, the most significant PBDE concentrations were recorded in gills. Also, a comparative analysis of POPs concentration in fish samples from Antarctic area was included. [ABSTRACT FROM AUTHOR]

Antifreeze proteins (AFPs) of polar marine teleost fishes are widely recognized as an evolutionary innovation of vast adaptive value in that, by adsorbing to and inhibiting the growth of internalized environmental ice crystals, they prevent death by inoculative freezing. Paradoxically, systemic accumulation of AFP-stabilized ice could also be lethal. Whether or how fishes eliminate internal ice is unknown. To investigate if ice inside high-latitude Antarctic notothenioid fishes could melt seasonally, we measured its melting point and obtained a decadal temperature record from a shallow benthic fish habitat in McMurdo Sound, Antarctica. We found that AFP-stabilized ice resists melting at temperatures above the expected equilibrium freezing/melting point (eqFMP), both in vitro and in vivo. Superheated ice was directly observed in notothenioid serum samples and in solutions of purified AFPs, and ice was found to persist inside live fishes at temperatures more than 1 °C above their eqFMP for at least 24 h, and at a lower temperature for at least several days. Field experiments confirmed that superheated ice occurs naturally inside wild fishes. Over the long-term record (1999-2012), seawater temperature surpassed the fish eqFMP in most summers, but never exceeded the highest temperature at which ice persisted inside experimental fishes. Thus, because of the effects of AFP-induced melting inhibition, summer warming may not reliably eliminate internal ice. Our results expose a potentially antagonistic pleiotropic effect of AFPs: beneficial freezing avoidance is accompanied by melting inhibition that may contribute to lifelong accumulation of detrimental internal ice crystals. [ABSTRACT FROM AUTHOR]

The article discusses the increment in the susceptibility to oxidative damage for the Notothenioidei fish and the environmental perturbations brought by the climate change. Topics discussed include information on the ability of Antarctic fish, changes in the total enzymatic activity of catalase and acclimation to decreased seawater pH. Also mentioned is that the ability of Notothenioidei fishes to predict the antioxidant capacity of oceans.

A number of Antarctic fish species are affected by an unusual gill condition known as X-cell disease, named in reference to morphologically similar lesions of unknown aetiology reported from northern hemisphere fishes. Despite the disease being first recorded in Antarctic fishes over 25 years ago, no progress has been made in identifying its cause or in confirming any possible relationship with northern fishes. Although once thought to be a neoplasm, observations of lesions in non-Antarctic fishes point towards a parasitic origin. The life cycle of the proposed causal organism is unknown, however, and the only stages identified are those of the eponymous cells in the lesions. Here, we show X-cells in diseased gills of the Antarctic nototheniid Trematomus bernacchii represent multinucleate cysts of an unknown parasitic organism. Furthermore, we use molecular genetic methodology to show that the organism responsible is closely related to that identified in X-cell lesions of the common European dab, Limanda limanda and that the disease thus has a global distribution. Phylogenetic tree construction based on 18S rDNA sequences confirms that X-cell organisms form a group of closely related parasites, but robust positioning of the X-cell clade in the tree awaits more extensive genetic sequencing. [ABSTRACT FROM AUTHOR]

Although it has been reported that Notothenia rossii elsewhere hatches in spring, our daily increment back-counting from the capture date in otoliths of fingerlings caught in Potter Cove, South Shetland Islands, in the 2000s, showed two main periods of larval hatching, one in summer (February-March) and another in winter (July). In concordance, the simultaneous presence of two cohorts born the same year was identified in the age/length frequency distribution of fish sampled in spring 2010, which belonged to biological ages 0+ and 1+ and hatched, respectively, in summer and winter-spring. Maximum and minimum ages of pelagic blue-phase and demersal brown-phase fingerlings were, respectively, 227 and 240 days, indicating a demersal settlement after about 8 months from hatching. The estimated growth rate was 0.23-0.33 mm/day, equivalent to that of South Georgia fingerlings and higher than those of other nototheniids of similar size range. Based on early life events associated with the hatching periods, two types of life cycles are hypothesised for South Shetland fingerlings. The pelagic blue-phase fingerlings (6.5-7.6 cm TL, age group 0+) hatched in July (winter cohort), entering in Potter Cove in February-March. The brown-phase fingerlings (6.3-10.6 cm, mostly of age group 0+) hatched in February-March (summer cohort) and were collected in the cove in spring (the smaller specimens) or in summer (the larger ones). Finally, early juveniles (10.7-15.5 cm, age group 1+) hatched in winter, mainly in July (winter cohort), entering in the cove the following year to spend the second winter inshore. [ABSTRACT FROM AUTHOR]

Background The notothenioids comprise a diverse group of fishes that rapidly radiated after isolation by the Antarctic Circumpolar Current approximately 14-25 million years ago. Given that evolutionary adaptation has led to finely tuned traits with narrow physiological limits in these organisms, this system provides a unique opportunity to examine physiological trade-offs and limits of adaptive responses to environmental perturbation. As such, notothenioids have a rich history with respect to studies attempting to understand the vulnerability of polar ecosystems to the negative impacts associated with global climate change. Unfortunately, despite being a model system for understanding physiological adaptations to extreme environments, we still lack fundamental molecular tools for much of the Nototheniidae family. Results Specimens of the emerald notothen, Trematomus bernacchii, were acclimated for 28 days in flow-through seawater tanks maintained near ambient seawater temperatures (-1.5°C) or at +4°C. Following acclimation, tissue specific cDNA libraries for liver, gill and brain were created by pooling RNA from n = 5 individuals per temperature treatment. The tissue specific libraries were bar-coded and used for 454 pyrosequencing, which yielded over 700 thousand sequencing reads. A de novo assembly and annotation of these reads produced a functional transcriptome library of T. bernacchii containing 30,107 unigenes, 13,003 of which possessed significant homology to a known protein product. Digital gene expression analysis of these extremely cold adapted fish reinforced the loss of an inducible heat shock response and allowed the preliminary exploration into other elements of the cellular stress response. Conclusions Preliminary exploration of the transcriptome of T. bernacchii under elevated temperatures enabled a semi-quantitative comparison to prior studies aimed at characterizing the thermal response of this endemic fish whose size, abundance and distribution has established it as a pivotal species in polar research spanning several decades. The comparison of these findings to previous studies demonstrates the efficacy of transcriptomics and digital gene expression analysis as tools in future studies of polar organisms and has greatly increased the available genomic resources for the suborder Notothenioidei, particularly in the Trematominae subfamily. [ABSTRACT FROM AUTHOR]

Among all validation methods of age determination in fish, release of known age and marked specimens gives the most reliable information. We carried out a tag-recapture experiment on Notothenia rossii at Potter Cove, to validate, for first time for this species using this method, the principle of annual deposition of an annulus in scales and otoliths. Of 132 juvenile specimens (TL = 22.1–38.1 cm) tagged and released in successive years from 2004 to 2010, 7 were recaptured at the same site after periods of 1–13 months. In scales of five specimens recovered after 10–13 months, one extra annulus was laid down, exhibiting an additional winter zone of closely spaced sclerites. Consistently, the same analysis in two individuals marked and recaptured during the same summer, after 1–3 months at liberty, did not show the deposition of an additional annulus. All the fish tagged or recaptured during the experiment period (December to March) showed in their scales an edge zone of widely spaced sclerites, in agreement with the known pattern of growth in summer. Likewise, an analysis in selected specimens showed good consistency between the numbers of sclerites deposited in scales and the time of fish release. The comparative analysis between scales taken at recapture and otoliths of the same individual allowed a simultaneous counting of the annuli with complete correspondence. The growth in length of fish ranged from 0.5 to 6.1 cm, depending on the time of release. [ABSTRACT FROM AUTHOR]

Determining the timing, extent and underlying causes of interspecific gene exchange during or following speciation is central to understanding species' evolution. Antarctic notothenioid fish, thanks to the acquisition of antifreeze glycoproteins during Oligocene transition to polar conditions, experienced a spectacular radiation to >100 species during Late Miocene cooling events. The impact of recent glacial cycles on this group is poorly known, but alternating warming and cooling periods may have affected species' distributions, promoted ecological divergence into recurrently opening niches and/or possibly brought allopatric species into contact. Using microsatellite markers and statistical methods including Approximate Bayesian Computation, we investigated genetic differentiation, hybridization and the possible influence of the last glaciation/deglaciation events in three icefish species of the genus Chionodraco. Our results provide strong evidence of contemporary and past introgression by showing that: (i) a substantial fraction of contemporary individuals in each species has mixed ancestry, (ii) evolutionary scenarios excluding hybridization or including it only in ancient times have small or zero posterior probabilities, (iii) the data support a scenario of interspecific gene flow associated with the two most recent interglacial periods. Glacial cycles might therefore have had a profound impact on the genetic composition of Antarctic fauna, as newly available shelf areas during the warmer intervals might have favoured secondary contacts and hybridization between diversified groups. If our findings are confirmed in other notothenioids, they offer new perspectives for understanding evolutionary dynamics of Antarctic fish and suggest a need for new predictions on the effects of global warming in this group. [ABSTRACT FROM AUTHOR]

Background: Among the cold-adapted Antarctic notothenioid fishes, the high-latitude bald notothen Pagothenia borchgrevinki is particularly notable as the sole cryopelagic species, exploiting the coldest and iciest waters of the Southern Ocean. Because P. borchgrevinki is a frequent model for investigating notothenioid cold-adaptation and specialization, it is imperative that "omic" tools be developed for this species. In the absence of a sequenced genome, a well annotated reference transcriptome of the bald notothen will serve as a model of gene expression in the coldest and harshest of all polar marine environments, useful for future comparative studies of cold adaptation and thermal responses in polar teleosts and ectotherms. Results: We sequenced and annotated a reference transcriptome for P. borchgrevinki, with added attention to capturing the transcriptional responses to acute and chronic heat exposures. We sequenced by Roche 454 a normalized cDNA library constructed from pooled mRNA encompassing multiple tissues taken from environmental, warm acclimating, and acute heat stressed specimens. The resulting reads were assembled into 42,620 contigs, 17,951 of which could be annotated. We utilized this annotated portion of the reference transcriptome to map short Illumina reads sequenced from the gill and liver of environmental specimens, and also compared the gene expression profiles of these two tissue transcriptomes with those from the temperate model fish Danio rerio. From this, we identified a conserved group of 58 GO terms, in which terms related to transcription and its regulation, ubiquitin-protein ligase activity, protein ubiquitination, and protein binding among others are more prevalent in the bald notothen, suggesting the pertinent genes play essential roles in cold temperature functioning. Conclusion: We sequenced multiple tissue transcriptomes from native and heat-exposed experimental specimens of the high Antarctic, cryopelagic notothenioid P. borchgrevinki to construct a reference transcriptome. In a proof of concept, we utilized the annotated reference transcriptome to profile the gene expression patterns of gill and liver, and identified a suite of over and under-represented GO terms when compared to the tropical water zebrafish suggesting these functions may be important for surviving in freezing waters. The transcriptome resource from this study will aid future investigations of cold adaptation and thermal response of polar ectothermic species. [ABSTRACT FROM AUTHOR]

The study of spatial and temporal distribution and diversity of ichthyoplankton (fish eggs and larvae) can provide fisheries-independent information on the population dynamics and recruitment processes of marine fish species. Ichthyoplankton studies in the Southern Ocean have to date been largely constrained to the summer months. We analysed ichthyoplankton data collected from a year round, long term (2002-2008), plankton trawl sampling programme in a large fjord system (Cumberland Bay) at South Georgia, sub-Antarctic (54.25°S, 36.5°W) to assess temporal changes in larval fish diversity and abundance. Larvae of 22 species, representing nine families, were identified although three, Krefftichthys anderssoni (Myctophidae), Lepidonotothen nudifrons/Trematomus hansoni (Nototheniidae) and Champsocephalus gunnari (Channichthyidae), dominated abundance in all years. Significant seasonal and interannual differences in the larval fish assemblage were revealed by multivariate analyses. Estimates of larval growth are provided for five abundant species. Considerable inter-specific differences in relative larval growth rate were recorded but interannual variability within species was small. However, in the commercially important C. gunnari, multiple larval cohorts, representing a protracted spawning season, were observed to grow at different rates, and this may be related to temperature and/or food availability. A comparison with historical growth data from South Georgia suggests there has been little change in growth rate for the main species over the last three decades. [ABSTRACT FROM AUTHOR]

Notothenioid fishes of the Southern Ocean have evolved under cold and stable temperatures for millions of years. Due to rising temperatures in the Southern Ocean, investigating thermal limits and the capacities for inducing a temperature acclimation response in notothenioids has become of increasing interest. Here, we investigated effects of temperature acclimation on cardiorespiratory responses and cardiac and skeletal muscle energy metabolism in a benthic Antarctic notothenioid, Trematomus bernacchii. We acclimated specimens to −1, 2 and 4.5 °C for 14 days and quantified heart rates and ventilation rates during an acute increase in temperature. Ventilation rates showed an effect of acclimation both at initial steady-state acclimation conditions and during an acute temperature increase, suggesting a partial thermal compensatory response. However, acclimation did not affect heart rates at steady-state acclimation conditions and the temperatures at which onset of cardiac arrhythmia occurred, suggesting lack of inducible thermal tolerance in cardiac performance. Citrate synthase (CS), lactate dehydrogenase (LDH) and 3-hydroxyacyl dehydrogenase activities in skeletal muscle tissues suggested acclimation-induced shifts in metabolic fuel preferences, and a marked increase in LDH activity with acclimation to 4.5 °C showed an increase in anaerobic metabolism. In heart tissue, CS and LDH activities decreased with acclimation to 4.5 °C, suggesting reduced cardiac ATP production. Overall, the data suggest a partial acclimatory response to temperature by T. bernacchii and support the hypothesis that reduced cardiac acclimatory capacity may play a role in limiting the thermal plasticity of T. bernacchii. [ABSTRACT FROM AUTHOR]

Abstract: Genes involved in the calcium signalling pathway have a relationship with cold tolerance in many plants. The primary reaction to many different environmental stresses is an increase in the cytoplasmic Ca2+ concentration. Such variations in the Ca2+ concentration could change the activity of Ca2+-dependent protein functions, further regulating the expression of stress-related genes; therefore, the Ca2+ signalling pathway is involved in the biological stress reaction. The expression of the calcium-modulated protein gene, calmodulin, in Antarctic notothenioid fish (Dissostichus mawsoni) accounts for 0.23% of all transcripts, which is a very high level of expression in this cold-water fish. To elucidate the function of calmodulin (CaM) from Antarctic notothenioid fishes, we introduced the calmodulin (CaM) gene into tobacco plants using a viral vector based on pea early browning virus (PEBV). RT-PCR and Western blot results confirmed that the CaM gene was over-expressed in tobacco. Under low-temperature stress, the CaM transgenic plants exhibited faster growth than wild-type plants. The physiological and biochemical effects of the high-level expression of CaM in tobacco were analysed, and the changes in the electrolyte leakage activity and malondialdehyde content showed that CaM over-expression in tobacco increased the cold tolerance of the plants. These results demonstrate that CaM can possibly be used to enhance the low-temperature tolerance of plants. [Copyright &y& Elsevier]

Antarctic notothenioid fish display specializations related to cope with their chronically cold environment, such as high triacylglycerol (TAG) content in tissues. The metabolic fate of glycerol, a product of TAG mobilization, has not been studied in Antarctic fish. To assess the importance of glycerol as a substrate for gluconeogenesis and to determine whether this pathway is metabolically cold adapted (MCA), key hepatic enzyme activities were measured in Antarctic ( Notothenia coriiceps, Gobionotothen gibberifrons, and Chionodraco rastrospinosus) and non-Antarctic ( Dissostichus eleginoides, Patagonotothen ramsayi, and Eleginops maclovinus) notothenioid fish. Fructose 1,6-biphosphatase (FBP), phosphoenolpyruvate carboxykinase (PEPCK), and glycerol kinase (GK) activities were similar in both groups at common temperatures (1, 6, 11, or 21 °C). In particular, thermal sensitivity for the reactions catalyzed by FBP and PEPCK was analogous between Antarctic and non-Antarctic species, reflected by similar values for Arrhenius energy of activation ( E) and Q. Additionally, hepatic glycerol, glucose, and glycogen contents together with plasma glycerol and glucose concentrations were similar for all of the species studied. Our results do not support the concept of MCA in hepatic gluconeogenesis and may indicate that the use of glycerol as a precursor for glucose synthesis by this pathway is of low physiological importance in Antarctic fish. [ABSTRACT FROM AUTHOR]

Chionodraco hamatus and Trematomus bernacchii are perciforms, members of the fish suborder Notothenioidei that live in the Antarctic Ocean and experience very cold and persistent environmental temperature. These fish have biochemical and molecular features that allow them to live at these extreme cold temperatures. Fine tuning of the level of unsaturated fatty acids content in membrane is a key mechanism of living organisms to adapt to cold and high temperatures. Desaturases are key enzymes that synthesize unsaturated fatty acyl-CoAs from saturated fatty acids. We cloned and sequenced a Δ-desaturase gene and its cDNA of C. hamatus, and the cDNA of T. bernacchii. The coded proteins are virtually identical and share homology to other Δ-desaturase fish sequences. These proteins contain, in the first trans-membrane domain, two cysteine residues that may form a disulfur bond present in the corresponding membrane region of Δ-desaturase proteins of other Antarctic fish but not in Eleginops maclovinus that experiences higher environmental temperatures and in all other Δ-desaturase genes of mammals present in data bases. C. hamatus Δ-desaturase gene complements a Saccharomyces cerevisiae mutant lacking Δ-desaturase ( Ole1) gene. Analysis of sequence homology of the trans-membrane domains of Δ-desaturase and the cytoplasmic region of the same proteins of Antarctic fish, non-Antarctic fish and mammals suggest that the significant differences found in the homologous sequences of the first trans-membrane domain may be due to the specific lipid content of their membrane. [ABSTRACT FROM AUTHOR]

We reviewed photographic images of fishes from depths of 381–2282 m in Marguerite Bay and 405–2007 m in the Amundsen Sea. Marguerite Bay fishes were 33% notothenioids and 67% non-notothenioids. Channichthyids (47%) and nototheniids (44%) were the most abundant notothenioids. The deep-living channichthyid Chionobathyscus dewitti (74%) and the nototheniid genus Trematomus (66%) were the most abundant taxa within these two families. The most abundant non-notothenioids were the macrourid Macrourus whitsoni (72%) and zoarcids (18%). Amundsen Sea fishes were 87% notothenioids and 13% non-notothenioids, the latter exclusively Macrourus whitsoni. Bathydraconids (38%) and artedidraconids (30%) were the most abundant notothenioids. We observed that Macrourus whitsoni was benthopelagic and benthic and infested by large ectoparasitic copepods. Juvenile (42 cm) Dissostichus mawsoni was not neutrally buoyant and resided on the substrate at 1277 m. Lepidonotothen squamifrons was seen near and on nests of eggs in early December. A Pogonophryne sp. from 2127 m was not a member of the deep-living unspotted P. albipinna group. Chionobathyscus dewitti inhabited the water column as well as the substrate. The pelagic zoarcid Melanostigma gelatinosum was documented in the water column a few metres above the substrate. The zoogeographic character of the Marguerite Bay fauna was West Antarctic or low-Antarctic and the Amundsen Sea was East Antarctic or high-Antarctic. [ABSTRACT FROM PUBLISHER]

Abstract: Population genetics patterns of marine fish in general and of Southern Ocean fish in particular range from virtual panmixia over ocean-wide scale to deeply fragmented populations. However the causes underlying these different patterns are not properly understood. In this paper, we tested the hypotheses that population connectivity is positively related to a combination of life history traits, namely duration of pelagic larval period and the tendency towards pelagic life style in the adulthood. To do so, we analysed the variability of six microsatellite and one mitochondrial marker (cytochrome b) in three Southern Ocean fish species (Trematomus newnesi, Trematomus hansoni and Trematomus bernacchii). They share a recent common ancestor but notably differ in their duration of pelagic larval period as well as pelagic versus benthic lifestyle. We sampled over a range of more than 5000km for all three species and used a number of population genetics tools to investigate past and contemporary levels of connectivity. All species experienced population fluctuations, but coalescent simulations suggested that contemporary populations are in migration-drift equilibrium. Although global FST values were rather low, a significant population structure separated the High-Antarctic from the Peninsular regions in all species. The level of genetic differentiation was much lower in the pelagic versus benthic species. Present data suggest that past and present genetic structuring in the Southern Ocean are indeed related with the ecological traits of Antarctic fish, however the relative importance of individual factors remains unclear. [Copyright &y& Elsevier]

Abstract: The teleost suborder Notothenioidei is restricted to the Southern Ocean and has been described as a species flock spanning the whole of it. Within the suborder, the subfamily Trematominae is important for coastal Antarctic ecosystems. The eleven Trematomus species occupy a large range of ecological niches. The genus is monophyletic if the genus Pagothenia (two additional species) and Cryothenia amphitreta, also nested within it, are included. Although the Trematominae have received much interest, the relationships among these fourteen species are still unclear. Several recent studies have tried to resolve these interrelationships; however no complete and clear picture has emerged, probably because of the use of a low number of insufficiently variable markers. The only common results places T. scotti as the sister-group of the rest of the subfamily and T. loennbergi close to T. lepidorhinus. We use here more variable markers. Four nuclear markers, two of which are new, and a mitochondrial marker for the biggest trematomine sampling ever gathered (14 species, 78 specimens). We found that several nuclear haplotypes are shared by several species (mostly in very closely related species). The haplotype patterns coupled with the cytogenetics of the subfamily suggest that a phenomenon of incomplete lineage sorting (ILS) is likely to be at play. Using a calibration linked to fossil evidence, we evaluate the relative ages of each clade within the Trematominae to assess the proximity of the speciation events to one another. The main trematomine diversification was recent and sudden. [Copyright &y& Elsevier]

An isolated partial right dentary (BAS D.515.2) collected by the British Antarctic Survey prompted a re-evaluation of gadiform remains from the La Meseta Formation (conventionally middle Eocene) of Isla Marambio (Seymour Island), Antarctic Peninsula. Modern gadiforms (hakes and cods) range from the Arctic to Antarctic, inhabiting deep sea benthic, shore, estuarine, and freshwater environments. Based on a fossil record primarily composed of otoliths, they are known to extend back to the Eocene and Oligocene. The new specimen was recovered from the fossil penguin locality D.515. It is characterized by a single row of sharp, ankylosed teeth set upon robust bony pedestals. The surface anterior to the mental foramen exhibits ascending and descending ridges with slightly rugose texture. The ascending ridge is fractured, but partially covers the lateral aspect of the tooth row. BAS D.515.2 is unlike the dentary of macrourid gadiforms, also recovered from the Eocene of Antarctica. BAS D.515.2 preserves several features similar to previously published accounts of the gadiform “†Mesetaichthys” from Isla Marambio. These specimens are probably the same taxon and their combined character suite indicates it is a member of Merluccidae. Thus, these are the only non-otolithic skeletal specimens of an Eocene hake known outside of the London Clay's †Rhinocephalus. [ABSTRACT FROM AUTHOR]

Parvalbumins (PVs) from Antarctic notothenioid fishes display a pattern of thermal adaptation that likely reflects evolutionary changes in protein conformational flexibility. We have used ancestral sequence reconstruction and homology modeling to identify two amino acid changes that could potentially account for the present thermal sensitivity pattern of Antarctic fish PVs compared with a PV from a theoretical warm-adapted ancestral fish. To test this hypothesis, ancient PVs were resurrected in the lab using PV from the notothenioid Gobionotothen gibberifrons as a platform for introducing mutations comparable to the reconstructed ancestral PV sequences. The wild-type PV (WT) as well as three mutant expression constructs were engineered: lysine 8 to asparagine (K8N), lysine 26 to asparagine (K26N) and a double mutant (DM). Calcium equilibrium dissociation constants (Kd) versus temperature curves for all mutants were right-shifted, as predicted, relative to that of WT PV. The Ka values for the K8N and K26N single mutants were virtually identical at all temperatures and showed an intermediate level of thermal sensitivity. The DM construct displayed a full conversion of thermal sensitivity pattern to that of a PV from a warm/temperate-adapted fish. Additionally, the Kd versus temperature curve for the WT construct revealed greater thermal sensitivity compared with the mutant constructs. Measurements of the rates of Ca2+ dissociation (Koff) showed that all mutants generally had slower koff values than WT at all temperatures. Calculated rates of Ca2+ binding (kon) for the K8N and K26N mutants were similar to values for the WT PV at all temperatures. In contrast, the calculated kon values for the DM PV were faster, providing mechanistic insights into the nature of potentially adaptive changes in Ca2+ binding in this PV. The overall results suggest that the current thermal phenotype of Antarctic PVs can be recapitulated by just two amino acid substitutions. [ABSTRACT FROM AUTHOR]

Among the endemic notothenioid fish of Antarctica, the Antarctic silverfish ( Pleuragramma antarcticum) is the only species in which all developmental stages live throughout the water column. It is widely distributed in the shelf waters around the continent, inhabiting both open waters and areas of pack ice at depths from 0 to 900 m. In successfully occupying this habitat, it evolved a suite of specific biological, ecological and physiological adaptations to the environmental conditions in the cold and highly seasonal Antarctic waters. Specialization for the pelagic environment evolved over millions of years enabled life under unusual environmental constraints and colonization of the pelagic realm of the Antarctic continental shelf. A sudden change of environmental conditions driven by the current rapid climate change could negatively affect this weak equilibrium, with a catastrophic cascade effecting higher trophic levels. Indeed, as both adults and early life stages of the Antarctic silverfish appear to be strongly dependent on sea-ice, this species would be especially sensitive to climatic or oceanic changes that reduce the extent of sea-ice cover or the timing of formation of coastal polynyas. [ABSTRACT FROM AUTHOR]

The goal of the ICEFISH 2004 cruise, which was conducted on board RVIB Nathaniel B. Palmer and traversed the transitional zones linking the South Atlantic to the Southern Ocean, was to compare the evolution, ecology, adaptational biology, community structure, and population dynamics of Antarctic notothenioid fishes relative to the cool/temperate notothenioids of the sub-Antarctic. To place this work in a comprehensive ecological context, cruise participants surveyed the benthos and geology of the biogeographic provinces and island shelves on either side of the Antarctic Polar Front (or Antarctic Convergence). Genome-enabled comparison of the responses of cold-living and temperate notothenioids to heat stress confirmed the sensitivity of the former to a warming Southern Ocean. Successful implementation of the international and interdisciplinary ICEFISH research cruise provides a model for future exploration of the sub-Antarctic sectors of the Indian and Pacific Oceans. [ABSTRACT FROM AUTHOR]

Many ectotherms rapidly acquire a short-lived increase in heat tolerance following a heat shock. This capacity to heat harden has been noted in a number of temperate fishes, but it is unknown whether it can also be found among the stenothermal Antarctic notothenioid fishes. To investigate, specimens of six notothenioid species were first brought to their critical thermal maxima (CTMax), and then following a recovery period of 4-24 h, a second CTMax was determined for each species to test for an increase in heat tolerance. All six species showed a significant increase over their initial CTMaxs, providing evidence for the existence of heat hardening in notothenioids. The magnitude of this increase ranged from 0.6 ± 0.29 to 1.8 °C ± 0.45, comparable to previously reported values from several temperate fishes and amphibians. This suggests that the heat hardening of Antarctic notothenioids remains undiminished despite their limited heat tolerance and provides further evidence that these fishes retain plasticity in their responses to heat despite their historical residence in a constant cold environment. [ABSTRACT FROM AUTHOR]

For the past 10 to 13 million years, Antarctic notothenioid fish have undergone extraordinary periods of evolution and have adapted to a cold and highly oxygenated Antarctic marine environment. While these species are considered an attractive model with which to study physiology and evolutionary adaptation, they are poorly characterized at the molecular level, and sequence information is lacking. The transcriptomes of the Antarctic fishes Notothenia coriiceps, Chaenocephalus aceratus, and Pleuragramma antarcticum were obtained by 454 FLX Titanium sequencing of a normalized cDNA library. More than 1,900,000 reads were assembled in a total of 71,539 contigs. Overall, 40% of the contigs were annotated based on similarity to known protein or nucleotide sequences, and more than 50% of the predicted transcripts were validated as full-length or putative full-length cDNAs. These three Antarctic fishes shared 663 genes expressed in the brain and 1,557 genes expressed in the liver. In addition, these cold-adapted fish expressed more Ub-conjugated proteins compared to temperate fish; Ub-conjugated proteins are involved in maintaining proteins in their native state in the cold and thermally stable Antarctic environments. Our transcriptome analysis of Antarctic notothenioid fish provides an archive for future studies in molecular mechanisms of fundamental genetic questions, and can be used in evolution studies comparing other fish. [ABSTRACT FROM AUTHOR]

The mackerel icefish ( Champsocephalus gunnari Lönnberg, 1905) is a ray-finned fish living in the Southern Ocean around Antarctica. We sequenced the complete mitochondrial (mt) genome of the mackerel icefish and a segment from cytochrome b to the control region (CR) in 32 individuals. The mt genome of the mackerel icefish was rearranged, containing two nicotinamide adenine dinucleotide (reduced form) dehydrogenase subunit 6 ( ND6), two tRNAGlu, and two CRs. However, variations in numbers of ND6 and tRNAGlu were observed amongst individuals. These variations included type 1 (containing two ND6 and two tRNAGlu), type 2 (containing one ND6, one incomplete ND6, and one tRNAGlu), and type 3 (containing one ND6 and one tRNAGlu). The gene orders of types 1 and 2, and variations in numbers of ND6 and tRNAGlu were not previously found in any Antarctic notothenioids, whereas type 3 is the same as that of Racovitzia glacialis. Phylogenetic analyses of CR DNA sequences showed that duplicated CRs of the same species formed a monophyletic group, suggesting that duplication of CRs occurred in each species. The frequent duplication of mt genomes in Antarctic notothenioids is an unusual feature in vertebrates. We propose that interspecific hybridization and impairment of mismatch repair might account for the high frequency of gene duplications and rearrangement of mt genomes in Antarctic notothenioids. [ABSTRACT FROM AUTHOR]

Trematomus newnesi is a common inshore species with a circum-Antarctic distribution. It provides the only known example of phenotypic plasticity in Antarctic notothenioid fish, existing as populations of typical, large mouth and intermediate morphs that can be difficult to identify. Using specimens from both Potter Cove, King George/25 de Mayo Island, and from McMurdo Sound, we found that the morphometric measurements gape width/head length (HL), upper jaw length/HL and, to a lesser extent, orbit diameter/HL reliably separated the morphs. For use in a key, we converted the ratios into the qualitative characters head shape, head width and upper jaw length relative to middle of the eye. To increase the reliability of the key, we also assessed intra-morph variability in these characters. The key is supplemented with colour photographs illustrating the distinctive features for separation of the morphs. We discovered that, in the case of the specimens from Potter Cove, each morph had a distinct pattern of colouration: typical-trunk blotched, with yellow or orange-brown predominating especially on pectoral and caudal fins; large mouth-trunk blotched, with green predominating especially in pectoral and opercular regions; and intermediate-trunk less blotched, with homogeneous dark brown-grey on trunk, pectoral and caudal fins. We also discuss the ecological implications of colour in the morphs. [ABSTRACT FROM AUTHOR]

Abstract: The Antarctic marine environment is one of the most extreme on Earth due to its stably low temperature and high oxygen content. Here we discuss various aspects of the molecular adaptations evolved by Antarctic fish and marine microorganisms living in this environment. This review will in particular focus on: (i) the genetic/genomic bases of adaptation in Antarctic notothenioid fish; (ii) the role of neuroglobin recently identified in the brain of Antarctic icefish; (iii) the structural and functional features of globins of the Antarctic marine bacterium Pseudoalteromonas haloplanktis TAC125. [Copyright &y& Elsevier]

As the Southern Ocean cooled to −1.8 °C over the past 40 My, the teleostean clade Notothenioidei diversified and, under reduced selection pressure for an oxygen-transporting apparatus, became less reliant on hemoglobin and red blood cells. At the extreme of this trend, the crown group of Antarctic icefishes (Channichthyidae) lost both components of oxygen transport. Under the decreased selection scenario, we hypothesized that the Antarctic dragonfishes (Bathydraconidae, the red-blooded sister clade to the icefishes) evolved lower blood hemoglobin concentrations because their globin gene complexes (α- and β-globin gene pairs linked by a regulatory intergene) transcribe globin mRNAs less effectively than those of basal notothenioids (e.g., the Nototheniidae [notothens]). To test our hypothesis, we 1) sequenced the α/β-intergenes of the adult globin complexes of three notothen and eight dragonfish species and 2) measured globin transcript levels in representative species from each group. The typical nototheniid intergene was ∼3–4 kb in length. The bathydraconid intergenes resolved into three subclasses (long [3.8 kb], intermediate [3.0 kb], and short [1.5–2.3 kb]) that corresponded to the three subclades proposed for the taxon. Although they varied in length due to indels, the three notothen and eight dragonfish intergenes contained a conserved ∼90-nt element that we have previously shown to be required for globin gene transcription. Using the quantitative polymerase chain reaction, we found that globin mRNA levels in red cells from one notothen species and from one species of each dragonfish subclade were equivalent statistically. Thus, our results indicate that the bathydraconids have evolved adult globin loci whose regulatory intergenes tend to be shorter than those of the more basal nototheniids yet are equivalent in transcriptional efficacy. Their low blood hemoglobin concentrations are most likely due to reduction in hematocrit. [ABSTRACT FROM PUBLISHER]

Abstract: To investigate the genomic architecture underlying the quintessential adaptive phenotype, antifreeze glycoprotein (AFGP) that enables Antarctic notothenioid survival in the frigid Southern Ocean, we isolated the AFGP genomic locus from a bacterial artificial chromosome library for Dissostichus mawsoni. Through extensive shotgun sequencing of pertinent clones and sequence assembly verifications, we reconstructed the highly repetitive AFGP genomic locus. The locus comprises two haplotypes of different lengths (363.6kbp and 467.4kbp) containing tandem AFGP, two TLP (trypsinogen-like protease), and surprisingly three chimeric AFGP/TLP, one of which was previously hypothesized to be a TLP-to-AFGP evolutionary intermediate. The ~100kbp haplotype length variation results from different AFGP copy number, suggesting substantial dynamism existed in the evolutionary history of the AFGP gene family. This study provided the data for fine resolution sequence analyses that would yield insight into the molecular mechanisms of notothenioid AFGP gene family evolution driven by Southern Ocean glaciation. [Copyright &y& Elsevier]

Abstract: Pelagic fish assemblages and community structure were examined along longitudinal and meridian transects off Adélie and George V Land, East Antarctica, in the austral summer 2008. Fish were sampled with an RMT 8 net principally from six discrete depth layers (0–50–100–200–500–1000–2000 m) in the oceanic zone and from three depth layers (0–50–100–200 m) over the continental shelf zone. A total of 20,281 individuals from 27 species were collected. Pleuragramma antarcticum was the most dominant species by number (18,710 inds), followed by Chionodraco hamatus (768), Trematomus newnesi (375), Cyclothone microdon (101), Electrona antarctica (92), Bathylagus antarcticus (51) and Notolepis coatsi (54). Cluster analysis revealed that the fish community was clearly divided at the Antarctic Slope Front into separate oceanic and shelf assemblages, being dominated by mesopelagic fish and notothenioids, respectively. The Southern Boundary of Antarctic Circumpolar Current likely restricted a more northern distribution of notothenioids in the upper 200 m. Mesopelagic fish dominated the large biomass below 500 m and notothenioids dominated that in the upper 100 m. It is considered that mesopelagic fish in the oceanic zone would unlikely be eaten by seabirds because no distinctive diel vertical migration to the surface layer was observed. In the neritic zone, notothenioids (C. hamatus, T. newnesi and P. antarcticum) possibly play an important role as prey items for flying seabirds, penguins and other notothenioids fish especially in the shallow depth stratum (0–100 m). [Copyright &y& Elsevier]

Abstract: The feeding ecology of the notothenioid fish Pleuragramma antarcticum was studied in the Dumont d’Urville Sea (East Antarctica) near the French Antarctic station. Stable isotopes (δ13C and δ15N) and diet contents were used in order to study dietary shifts between fish larvae and juveniles. All specimens had low δ13C values (<−24‰), a main characteristic of high-Antarctic pelagic species. Fish larvae showed differences in both carbon and nitrogen ratios when compared with juveniles. Muscle δ15N values showed a difference of one trophic level (∼3‰) between larvae (6.7‰) and juveniles (9.7–10.0‰) and a trophic position of tertiary consumers. Diet content analyses (stereomicroscope and scanning electron microscopes) indicated that larvae are omnivorous, feeding on phytoplankton (mainly diatoms) as well as on zooplankton species. A positive relationship between δ15N values and size was found and indicated a carnivorous diet for older specimens. [Copyright &y& Elsevier]

Abstract: The RSV Aurora Australis survey allowed the first comprehensive study of the demersal ichthyofaunal environment and of the diversity of the Dumont d’Urville Sea. We observed a high dominance of the Notothenioidei in both the number of species and in integrated abundances. The Nototheniidae was the most abundant family with 44.7% of the total integrated abundance, followed by Bathydraconidae (18.8%). Trematomus eulepidotus was the dominant species with 19.9% of the total individuals catch. Nevertheless, 43 of the 53 species caught could be considered as very rare. The Bathydraconidae was the most diversified family with 11 species caught. The highest integrated abundances of fish were found from 400 to 800m. Well-structured species communities were observed, with high species richness from 570 to 681m. The richest zones were located along the basins and along their upper-sides. Statistical analyses indicated large-scale spatial patterns in species composition, with clear differences in fish communities from the continental slopes, the basins and on the shelf. At a finer spatial scale, the current in the George V Basin and iceberg scouring on the banks and their sides tended to create locally heterogeneous small-scale habitats. We suggest that the glacial history and the structured habitats allowed successive colonisations of the seabed by demersal fish. [Copyright &y& Elsevier]

edidraconids (Plunderfishes) are small benthic notothenioid fishes of the Antarctic and South Georgia shelf and slope. The family Artedidraconidae is monophyletic; however, the relationships within the family have remained poorly explored until now, and based on a small sample of the genus Artedidraco. The present study focuses on the interrelationships among the artedidraconid genera and the phylogeny of the genus Artedidraco. 2,353 base pairs from 77 specimens were sequenced from the partial mitochondrial cytochrome oxidase I gene and cytochrome b gene, the partial mitochondrial control region and the partial nuclear rhodopsin retrogene. The genus Artedidraco is not monophyletic, confirming the preliminary relationships found by Derome et al. (Mol Phylogenet Evol 24:139-152, ): Pogonophryne, Dolloidraco and Histiodraco are well embedded within the genus Artedidraco. From Artedidraco skottsbergi and A. loennbergi to A. orianae and A. mirus, the tree shows that there is an increasing number of upper lateral line tubular scales and decreasing number of disc-shaped scales. There is also a trend toward a decrease in the number of epipleural ribs and an increase in number of pleural ribs along the tree. [ABSTRACT FROM AUTHOR]

Abstract: The Southern Ocean is home to two major types of fishes: the largely endemic suborder Notothenioidei and representatives of oceanic fish families that are widely distributed in the midwater and benthic environments elsewhere (e.g. bathylagids, myctophids, liparids, and zoarcids). In most regions of the coastal Antarctic, e.g. the Ross Sea, there is a distinct separation in the pelagic communities at the shelf break between the oceanics (off-shelf) and the endemics (on-shelf). Coincidentally, in much of the coastal Antarctic, the shelf break also marks the boundary between a water column entirely composed of the very cold (−2°C) Ice Shelf Water and an oceanic profile that includes warmer circumpolar deep water (2°C at 200m) at intermediate depths. The distinct separation in pelagic communities observed in most coastal regions of the Antarctic is not seen on the western Antarctic Peninsula (WAP), where circumpolar deep water intrudes to form a warmer midwater and oceanic species are strongly represented. It was hypothesized that the cold ice-shelf water, lethal to fishes without antifreeze glycoproteins (AFGPs) in their blood, was excluding the oceanic species from most of the Antarctic continental shelf waters. To test the hypothesis, nine species of fish captured in WAP shelf waters were tested for the presence of AFGPs. The oceanic fish families analyzed: Myctophidae (Electrona and Gymnoscopelus), Zoarcidae (Melanostigma), Gempylidae (Paradiplospinus), Paralepididae (Notolepis), and Bathylagidae (Bathylagus) showed no antifreeze activity. Two endemic species captured in the same sampling program did show antifreeze activity: the important pelagic species Pleuragramma antarcticum (Nototheniidae) and the Bathydraconid species Vomeridens infuscipinnus. The absence of AFGPs in the blood of Antarctic oceanic species makes a strong case for temperature exclusion of oceanic fishes in the coastal Antarctic. [Copyright &y& Elsevier]

Abstract: The adaptive radiation of the Antarctic notothenioid ancestral benthic fish stock within the chronic freezing waters of the Southern Ocean gave rise to five highly cold adapted families. Their stenothermy, first observed from several high-latitude McMurdo Sound species, has been of increasing recent interest given the threat of rising polar water temperatures from global climate change. In this study we determined the heat tolerance in a geographically diverse group of 11 Antarctic species as their critical thermal maximum (CTMax). When acclimatized to their natural freezing water temperatures, environmental CTMaxs ranged from 11.95 to 16.17°C, well below those of fishes endemic to warmer waters. There was a significant regional split, with higher CTMaxs in species from the more northerly and thermally variable Seasonal Pack-ice Zone. When eight of the Antarctic species were warm acclimated to 4°C all showed a significant increase over their environmental CTMaxs, with several showing plasticity comparable in magnitude to some far more eurythermal fishes. When the accrual of heat tolerance during acclimation was followed in three high-latitude McMurdo Sound species, it was found to develop slowly in two of them, which was correlated with their low metabolic rates. [Copyright &y& Elsevier]

The article presents a study on the effect of global warming on Notothenioids, a taxonomic group that dominates Antarctic fish. It notes that the genetic constraints of this group limits their adaptation to climate change specifically the scenario in Southern Ocean. An observation on Trematomus bernacchii, an Antarctic fish, responding to heat stress suggests a lack of specific heat-shock response. A study of macro- and micro-evolutionary processes of Notothenioids is said to be essential to understand better how they can cope with climate change.

Adaptive radiation is usually triggered by ecological opportunity, arising through (i) the colonization of a new habitat by its progenitor; (ii) the extinction of competitors; or (iii) the emergence of an evolutionary key innovation in the ancestral lineage. Support for the key innovation hypothesis is scarce, however, even in textbook examples of adaptive radiation. Antifreeze glycoproteins (AFGPs) have been proposed as putative key innovation for the adaptive radiation of notothenioid fishes in the ice-cold waters of Antarctica. A crucial prerequisite for this assumption is the concurrence of the notothenioid radiation with the onset of Antarctic sea ice conditions. Here, we use a fossil-calibrated multi-marker phylogeny of nothothenioid and related acanthomorph fishes to date AFGP emergence and the notothenioid radiation. All timeconstraints are cross-validated to assess their reliability resulting in six powerful calibration points. We find that the notothenioid radiation began near the Oligocene-Miocene transition, which coincides with the increasing presence of Antarctic sea ice. Divergence dates of notothenioids are thus consistent with the key innovation hypothesis of AFGP. Early notothenioid divergences are furthermore congruent with vicariant speciation and the breakup of Gondwana. [ABSTRACT FROM AUTHOR]

We characterized nine polymorphic microsatellites by an enriched library from the Antarctic silverfish Pleuragramma antarcticum, a key species in the high Antarctic zone of the Southern Ocean. The number of alleles scored ranged from 7 to 39, whereas the observed and expected heterozygosity ranged from 0.4000 to 0.9750 and from 0.3943 to 0.9782, respectively. Cross-amplification was tested in the 3 species of the genus Chionodraco (Channichthyidae). These new microsatellites could potentially be useful in further investigations on P. antarcticum for which many questions on population structure and exposition to global environment change are still open to debate. [ABSTRACT FROM AUTHOR]

Abstract: Rolling-circle (RC) eukaryotic transposons, known as helitrons, are found in a wide range of organisms, from protist to mammals. Autonomous helitrons have a distinctive open reading frame (ORF) encoding a polypeptide that contains typical domains for RC replication (RCR): the Rep (RCR initiator) and the DNA helicase domains. These elements are believed to have an important role in the host genome evolution, owing to their frequent capture of host genes, some of which can evolve into novel genes or become essential for helitron transposition. We conducted a molecular analysis of the suborder Notothenioidei, a group of Perciformes that currently dominate the Antarctic waters by virtue of their remarkable cold-adaptation ability. A novel helitron from the genome of the icefish species Chionodraco hamatus, belonging to the Channichthyidae, the most derived Notothenioids family, was isolated, characterized and designated as HeliNoto (8.9kb). Its ORF was compared to homologous sequences from different species in a comprehensive phylogenetic analysis. For the first time the putative functional domains of a helitron were subjected to a well accurate structural analysis including chromosomal localization. Finally, the distribution of HeliNoto among Notothenioids was investigated. [Copyright &y& Elsevier]

The perciform suborder Notothenoidei provides a compelling opportunity to study the adaptive radiation of a marine species-flock in the cold Southern Ocean that surrounds Antarctica. To facilitate genome-level studies of the diversification of these fishes, we present estimates of the genome sizes of 11 Antarctic species and describe the production of high-quality bacterial artificial chromosome (BAC) libraries for two, the red-blooded notothen Notothenia coriiceps and the white-blooded icefish Chaenocephalus aceratus. Our results indicate that evolution of phylogenetically derived notothenioid families (e.g., the crown group Channichthyidae [icefishes]), was accompanied by genome expansion. Six species from the basal family Nototheniidae had C-values between 0.98 and 1.20 pg, a range that is consistent with the genome sizes of proposed outgroups (e.g., percids) of the notothenioid suborder. In contrast, four icefishes had C-values in the range 1.66–1.83 pg. The BAC libraries VMRC-19 (N. coriiceps) and VMRC-21 (C. aceratus) comprise 12× and 10× coverage of the respective genomes and have average insert sizes of 138 and 168 kb. Paired BAC-end reads representing ∼0.1% of each genome showed that the repetitive element landscapes of the two genomes (13.4% of the N. coriiceps genome and 14.5% for C. aceratus) were similar. The availability of these high-quality and well-characterized BAC libraries sets the stage for targeted genomic analyses of the unusual anatomical and physiological adaptations of the notothenioids, some of which mimic human diseases. Here we consider the evolution of secondary pelagicism by various taxa of the group and illustrate the utility of Antarctic icefishes as an evolutionary-mutant model of human osteopenia (low-mineral density of bones). [ABSTRACT FROM AUTHOR]

Antarctic plunderfishes (Notothenioidei, Artedidraconidae) are important components of the Southern Ocean fish fauna. As a contribution to the Victoria Land Transect Project, we performed a cytogenetic analysis of six species from three of the four artedidraconid genera, Artedidraco glareobarbatus, A. orianae, A. skottsbergi, A. shackletoni, Histiodraco velifer, and Pogonophryne sp. We investigated the species-specific cytogenetic features and highlighted patterns of chromosomal evolutionary change using a molecular phylogeny based on mitochondrial and nuclear genes. Despite a conserved diploid number, some important karyotypic traits account for major differences among artedidraconid species. Specific cytogenetic features, including the chromosomal organization of ribosomal genes and the occurrence of sex chromosomes, are characteristics of A. skottsbergi, making this species distinct among those studied. These chromosomal peculiarities are consistent with the phylogenetic hypothesis resolving A. skottsbergi as the sister lineage of all other Artedidraconidae. A karyological similarity was found between A. glareobarbatus and A. shackletoni consistent with their inferred sister species relationship in the phylogeny. The results indicate that artedidraconids are not conservative in their genomic organization at the chromosomal level and provide new evidence for the degree of biological diversity in this notothenioid group. [ABSTRACT FROM AUTHOR]