Antarctic teleost immunoglobulins: more extreme, more interesting

We have investigated the immunoglobulin molecule and the genes encoding it in teleosts living in the Antarctic seas at the constant temperature of −1.86 °C. The majority of Antarctic teleosts belong to the suborder Notothenioidei (Perciformes), which includes only a few non-Antarctic species. Twenty-one Antarctic and two non-Antarctic Notothenioid species were included in our studies. We sequenced immunoglobulin light chains in two species and μ heavy chains, partially or totally, in twenty species. In the case of heavy chain, genomic DNA and the cDNA encoding the secreted and the membrane form were analyzed. From one species, Trematomus bernacchii, a spleen cDNA library was constructed to evaluate the diversity of VH gene segments. T. bernacchii IgM, purified from the serum and bile, was characterized. Homology Modelling and Molecular Dynamics were used to determine the molecular structure of T. bernacchii and Chionodraco hamatus immunoglobulin domains. This paper sums up the previous results and broadens them with the addition of unpublished data.     

Sex determination in Antarctic notothenioid fish: chromosomal clues and evolutionary hypotheses

In fish, the determination of sex can be controlled by genetic factors, environmental factors or a combination of both. The presence of heteromorphic sex-related chromosomes is widely acknowledged as strongly indicative of genetic control of sex determination (GSD) acting over other sex control systems. Heteromorphic sex-related chromosomes have been observed in a minority of teleosts (approximately 4 %). However, when looking at the fishes of the suborder Notothenioidei the frequency of sex-related chromosomes increases substantially, reaching 26.67 % of the cytogenetically studied species. Noteworthy, sex chromosomes were observed only in cold-adapted species which live in the Antarctic coastal waters, whereas morphologically differentiated sex chromosomes were never observed in the temperate non-Antarctic notothenioid families. Recent evidence suggests that the sex-linked chromosomes across the Antarctic notothenioid families may not share a common origin, but likely originated more than once during notothenioid evolutionary history, thus implying the presence of selection pressures operating toward fixation of GSD system. On the whole, the cytogenetic evidences suggest the Antarctic-specific fixation of differentiated heteromorphic sex-related chromosomes and of a prominent GSD across Antarctic notothenioids that may be an additional manifestation of notothenioid evolution in thermally stable cold environment.     

Hemoglobin from the Antarctic fish Notothenia coriiceps neglecta. 2. Amino acid sequence of the alpha chain of Hb1

The complete amino acid sequence of the alpha chain of the main hemoglobin of the Antarctic fish Notothenia coriiceps neglecta (family Nototheniidae) has been determined. It consists of 142 residues; an acetylated seryl residue is at the amino terminal. The molecular mass is 15,519 Da. In comparison with alpha-chain sequences of non-Antarctic poikilothermic fish hemoglobins, the homology appears to be significantly lower than that existing among the latter species. A higher homology has been found with the alpha-chain sequence of the non-poikilothermic bluefin tuna.     

Gluconeogenic pathway does not display metabolic cold adaptation in liver of Antarctic notothenioid fish

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 _a) and Q₁₀. 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.     

Analysis of dietary overlap in Antarctic fish (Notothenioidei) from the South Shetland Islands: no evidence of food competition

A dietary overlap analysis between notothenioid species was carried out among three fish assemblages in the South Shetland Island area. Using Tyler's (1972) method, the re-occurrence of main and secondary prey among fish predators was 33% in summer and 37% over the year at Potter Cove, 25% in summer and 7% in winter at Admiralty Bay, and 20% in autumn/winter around Elephant Island. Likewise, using the "S" index of Linton et al. (1981), the diet similarity between most species pairs is <50%. This relatively low dietary overlap may be explained by the about equally divided occurrence of generalised feeders and specialised feeders, with no evidence of competition among them. The fishes' trophic niches seem to be separated by depth and prey taxa. These findings are compared with other Antarctic fish communities and those in similar non-Antarctic cold marine ecosystems.     

Otolith Morphology and Relationships of Several Fish Species of the Suborder Scorpaenoidei

Journal of Ichthyology - Otolith (sagitta) morphology is described in six tropical fish species belonged to different genera of the suborder Scorpaenoidei: Synanceia horrida, Inimicus sinensis,...     

Antioxidant potential is positively correlated with mitochondrial enzyme activity in Antarctic and non-Antarctic notothenioid fishes

Antarctic notothenioid fishes possess high oxidative capacities, large amounts of intracellular lipid combined with biological membranes enriched in polyunsaturated fatty acids, all of which could make these animals susceptible to oxidative injury, particularly in the form of lipid peroxidation. The central objective in this study was to examine capacities for oxidative metabolism and total antioxidant defense in Antarctic and non-Antarctic notothenioids in order to test the hypothesis that the cold-bodied Antarctic fishes possess elevated activities of citrate synthase (CS), matched by a more robust antioxidant (AOX) defense, than non-Antarctic species. CS activities and total AOX capacities were measured in brain and heart of 4 Antarctic species and 2 non-Antarctic species collected on the 2004 ICEFISH cruise. While no statistical differences are found among Antarctic and non-Antarctic fishes in either CS or AOX capacities, AOX capacity in both tissues expands with CS activity among individuals measured when all species are combined. There is also a 4.5-fold greater AOX capacity, when normalized to CS activity, in brain than in heart indicating the requirement for extra AOX defense in a tissue well known for its particularly high levels of phospholipids more prone to lipid peroxidation.     

Some like it hot, some like it cold: the heat shock response is found in New Zealand but not Antarctic notothenioid fishes

Previous research on Antarctic notothenioids has demonstrated that cells of cold-adapted Antarctic notothenioids lack a common cellular defense mechanism called the heat shock response (HSR), the induction of a family of heat shock proteins (Hsps) in response to elevated temperatures. The goal of this study was to address how widespread the loss of the HSR is within the Notothenioidei suborder and, specifically, to ask whether cold temperate non-Antarctic notothenioids possess the HSR. In general, Antarctic fish have provided an important opportunity for physiologists to examine responses to selection in the environment and to ask whether traits of the notothenioids represent cold adaptation, or whether the traits are related to history and are characteristics of the notothenioid lineage. Using in vivo metabolic labeling, results indicate that one of the two New Zealand notothenioids possess an HSR. The thornfish, Bovichtus variegatus Richardson, 1846, expressed heat shock proteins (Hsp) in response to heat stress, whereas the black cod, Notothenia angustata Hutton, 1875, did not display robust stress-inducible Hsp synthesis at the protein-level. However, further analysis using Northern blotting clearly demonstrated that mRNA for a common Hsp gene, hsp70, was present in cells of both New Zealand species following exposure to elevated temperatures. Overall, combined evidence on the HSR in notothenioid fishes from temperate New Zealand waters indicate that the loss of the HSR in Antarctic notothenioid fishes occurred after the separation of Bovichtidae from the other Antarctic notothenioid families, and that the HSR was most likely lost during evolution at cold and constant environmental temperatures.     

Molecular taxonomy of the suborder Bodonina (Order Kinetoplastida), including the important fish parasite,Ichthyobodo necator

Ichthyobodo necator is an important fish ectoparasite with a broad host and ecological range. A novel method, involving the use of an anesthetic, allowed the collection of large numbers of parasites from the skin and gills of hybrid striped bass (Morone saxatilis male x M. chrysops female). Genomic DNA from these samples was used to amplify and clone the 18S rRNA gene. The 18S rRNA gene was similarly cloned from Bodo caudatus, Bodo edax, Bodo saltans, an unidentified Bodo species, and Dimastigella trypaniformis. The resulting sequences were aligned with other representative kinetoplastid species using pileup and similarities in secondary structure. Phylogenetic relationships within the suborder Bodonina and representatives of the suborder Trypanosomatina were determined using maximum-likelihood statistics. The phylogenetic analyses strongly supported the order Kinetoplastida as a monophyletic assemblage consisting of at least two major lineages. One lineage consisted exclusively of L. necator, indicating that it may represent a new suborder. The second lineage consisted of all other kinetoplastid species. This second lineage appeared to contain at least 8 bodonine sublineages, none of which correlated with currently recognized families. For three sublineages, there was a close correspondence between the 18S phylogeny and the classical taxonomy of Dimastigella, Rhynchobodo, and Rhynchomonas. In contrast, Bodo and Cryptobia were polyphyletic, containing species in two or more sublineages that may represent separate genera.     

Cloning and characterization of a Δ9-desaturase gene of the Antarctic fish Chionodraco hamatus and Trematomus bernacchii

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 Δ⁹-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 Δ⁹-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 Δ⁹-desaturase proteins of other Antarctic fish but not in Eleginops maclovinus that experiences higher environmental temperatures and in all other Δ⁹-desaturase genes of mammals present in data bases. C. hamatus Δ⁹-desaturase gene complements a Saccharomyces cerevisiae mutant lacking Δ⁹-desaturase (Ole1) gene. Analysis of sequence homology of the trans-membrane domains of Δ⁹-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.     

Variability in brain ganglioside composition: A further molecular mechanism beside serum antifreeze-glykoproteins for adaptation to cold in Antarctic and Arctic-boreal fishes

Summary Gangliosides and sialoglycoproteins from brain, liver and muscle have been isolated from 6 Antarctic fish species from the suborder Notothenoids and from 4 Arctic-boreal fish species. In addition freezing and melting points from serum of both groups were examined in order to determine the presence of protein antifreezes. In comparison with eurythermic fishes of temperate climates in both groups the phylogenetical adaptation to cold is correlated with a significantly higher concentration of gangliosides in the brain. The ganglioside concentration of liver in Antarctic fish, but not in Arctic species, is 3 to 5fold higher than in mammals (rat); in muscle the ganglioside content is increased only in red-blooded Antarctic fish as compared with mammals. The concentration of neuronal sialo-glycoproteins generally is lower in Antarctic fish than in other marine teleosts; in muscles the content is 2 to 3fold higher than in mammals. The molecular composition of brain gangliosides is characterized by an extreme high polarity which is due to an equipment with highly sialylated fractions (40 to 50% higher sialylated than tetrasialogangliosides). There are distinct differences between the freezing and melting point of blood serum, especially in the Antarctic species in favour of the existence of protein antifreezes. The results are discussed with regard to the fact that the extremely high polarity of brain gangliosides reflects a very efficient mechanism on molecular level to keep the neuronal membrane functional under low temperature conditions.     

Biochemical adaptations of notothenioid fishes: comparisons between cold temperate South American and New Zealand species and Antarctic species

Fishes of the perciform suborder Notothenioidei afford an excellent opportunity for studying the evolution and functional importance of diverse types of biochemical adaptation to temperature. Antarctic notothenioids have evolved numerous biochemical adaptations to stably cold waters, including antifreeze glycoproteins, which inhibit growth of ice crystals, and enzymatic proteins with cold-adapted specific activities (k(cat) values) and substrate binding abilities (K(m) values), which support metabolism at low temperatures. Antarctic notothenioids also exhibit the loss of certain biochemical traits that are ubiquitous in other fishes, including the heat-shock response (HSR) and, in members of the family Channichthyidae, hemoglobins and myoglobins. Tolerance of warm temperatures is also truncated in stenothermal Antarctic notothenioids. In contrast to Antarctic notothenioids, notothenioid species found in South American and New Zealand waters have biochemistries more reflective of cold-temperate environments. Some of the contemporary non-Antarctic notothenioids likely derive from ancestral species that evolved in the Antarctic and later "escaped" to lower latitude waters when the Antarctic Polar Front temporarily shifted northward during the late Miocene. Studies of cold-temperate notothenioids may enable the timing of critical events in the evolution of Antarctic notothenioids to be determined, notably the chronology of acquisition and amplification of antifreeze glycoprotein genes and the loss of the HSR. Genomic studies may reveal how the gene regulatory networks involved in acclimation to temperature differ between stenotherms like the Antarctic notothenioids and more eurythermal species like cold-temperate notothenioids. Comparative studies of Antarctic and cold-temperate notothenioids thus have high promise for revealing the mechanisms by which temperature-adaptive biochemical traits are acquired - or through which traits that cease to be of advantage under conditions of stable, near-freezing temperatures are lost - during evolution.     

The hemoglobins of the cold-adapted Antarctic teleost Cygnodraco mawsoni

The blood of the teleost Cygnodraco mawsoni, of the endemic Antarctic family Bathydraconidae, contains a major hemoglobin (Hb 1), accompanied by a minor component (Hb 2, about 5% of total). The two hemoglobins have identical alpha chains and differ by the beta chain. The complete amino acid sequence of the three chains has been elucidated, thus establishing the primary structure of both hemoglobins. The sequences show a 53-65% identity with non-Antarctic poikilotherm fish species; on the other hand, a very high degree of similarity (83-88%) has been found between Hb 1 and the major component of another Antarctic species of a different family. The hemoglobin functional properties relative to oxygen binding have been investigated in intact erythrocytes, 'stripped' hemolysate and purified components of C. mawsoni. The hemoglobins display the Bohr and Root effects, indicating fine regulation of oxygen binding by pH and by the physiological effectors organic phosphates.     

Structure and function of the Gondwanian hemoglobin of Pseudaphritis urvillii, a primitive notothenioid fish of temperate latitudes

The suborder Notothenioidei dominates the Antarctic ichthyofauna. The non-Antarctic monotypic family Pseudaphritidae is one of the most primitive families. The characterization of the oxygen-transport system of euryhaline Pseudaphritis urvillii is herewith reported. Similar to most Antarctic notothenioids, this temperate species has a single major hemoglobin (Hb 1, over 95% of the total). Hb 1 has strong Bohr and Root effects. It shows two very uncommon features in oxygen binding: At high pH values, the oxygen affinity is exceptionally high compared to other notothenioids, and subunit cooperativity is modulated by pH in an unusual way, namely the curve of the Hill coefficient is bell-shaped, with values approaching 1 at both extremes of pH. Molecular modeling, electronic absorption and resonance Raman spectra have been used to characterize the heme environment of Hb 1 in an attempt to explain these features, particularly in view of some potentially important nonconservative replacements found in the primary structure. Compared to human HbA, no major changes were found in the structure of the proximal cavity of the alpha-chain of Hb 1, although an altered distal histidyl and heme position was identified in the models of the beta-chain, possibly facilitated by a more open heme pocket due to reduced steric constraints on the vinyl substituent groups. This conformation may lead to the hemichrome form identified by spectroscopy in the Met state, which likely fulfils a potentially important physiological role.     

Morphological and biochemical variations in the gills of 12 aquatic air-breathing anabantoid fish

All fish species in the Anabantoidei suborder are aquatic air-breathing fish. These species have an accessory air-breathing organ, called the labyrinth organ, in the branchial cavity and can engulf air at the surface of the water to assist in gas exchange. It is therefore necessary to examine the extent of gill modification among anabantoid fish species and the potential trade-offs in their function. The experimental hypothesis that we aimed to test is whether anabantoid fishes have both morphological and functional variations in the gills among different species. We examined the gills of 12 species from three families and nine genera of Anabantoidei. Though the sizes of the fourth gill arch in three species of Trichogaster were reduced significantly, not all anabantoid species had morphological and functional variations in the gills. In these three species, the specific enzyme activity and relative protein abundance of Na(+)/K(+)-ATPase were significantly higher in the anterior gills as compared with the posterior gills and the labyrinth organ. The relative abundance of cytosolic carbonic anhydrase, an indicator of gas exchange, was found to be highest in the labyrinth organ. The phylogenetic distribution of the fourth gill's morphological differentiation suggests that these variations are lineage specific, which may imply a phylogenetic influence on gill morphology in anabantoid species.     

The Lepocreadiidae (Digenea) of fishes from the north-east Atlantic: review of the genusParalepidapedon Shimazu & Shimura, 1984, with a description ofP. williamsi n. sp.

A new species,Paralepidapedon williamsi, is described from the fishCottunculus microps and an unidentified fish of the suborder Cottoidei in the NE Atlantic Ocean. This species is the first member of the genus to be recognized in the Atlantic Ocean. Its general morphology is similar to that of the other members of the genus, but it is distinguished by its large eggs and the relatively few gland-cells associated with the external seminal vesicle. The genusParalepidapedon, which differs fromNeolepidapedon in the possession of a uroproct, is reviewed and a key to the species given. The genus is considered to include five species.     

Ribosomal genes in notothenioid fishes: Focus on the chromosomal organisation

This mini-review makes a survey and a summary of some major issues concerning the chromosomal organisation of ribosomal genes in fish genomes, by using Notothenioidei as the model. The increasing body of information, published during the last two decades on the chromosomal mapping of the two ribosomal genes classes (45S rDNA and 5S rDNA) in notothenioids, makes it possible to recognise the main evolutionary trends across the phylogeny of the group. As one of the major features, the rDNA clusters are organised in a single chromosomal locus in most of the species. This locus is located at different positions along the chromosomes in the basal groups (non-Antarctic Clade), whereas it maintains a strongly conserved location in the cold-adapted species (Antarctic Clade). Important structural changes, leading to the co-localisation of the two ribosomal gene classes, occurred early in the notothenioid phylogeny, perhaps in the common ancestor of the Eleginopidae and Nototheniidae. The cytogenetic evidences indicate that an increased amount of ribosomal genes, organised in two large chromosomal loci, is present in the giant Antarctic fish Dissostichus mawsoni. This gain in rRNA genes is an important genomic change, having possible implications for the fitness of this notothenioid fish that combines large size, pelagic lifestyle and cold-adaptation.     

Sheep haemopexin: immunological cross-reactivity with other vertebrate sera and evidence for the absence of haemopexin in some mouflon

A monospecific antiserum to sheep haemopexin was produced in rabbits. By using this antiserum, as well as absorbed antisera to sheep and mouflon serum proteins, it was proved that some mouflon sera lack haemopexin. In immunodiffusion, when using the monospecific antiserum, immunoprecipitates were present only in species' belonging to suborder Ruminantia. None of the other mammalian, nor any of the avian, reptilian, amphibian and fish species tested, showed reaction.     

Phylogeography of the Chionodraco genus (Perciformes,Channichthydae) in the Southern Ocean

Antarctic fish of the suborder Notothenioidei represent one of the most notable examples of adaptive radiation in the marine environment. The evolutionary relationships between and within the eight families of this suborder have been well established by numerous studies, whereas the microevolutionary processes of notothenioid species remain largely unexplored. In the present paper we investigated the evolutionary relationships between three closely related species of the genus Chionodraco (family Channichthyidae), namely Chionodraco hamatus, Chionodraco rastrospinosus, and Chionodraco myersi by analysing portions of the mitochondrial genome (D-loop and 16S rRNA). The taxonomic status of C. hamatus and C. rastrospinosus as separate species has been questioned because of the limited number of key morphological characters that distinguish these two taxa. Our results, based on the analysis of several specimens belonging to both morphological groups revealed a small genetic differentiation among haplotypes, however, a clear separation between the two nominal species emerged since all individuals of each of the two taxa clustered together in distinct monophyletic groups. C. myersi appeared more distantly related in the phylogenetic analysis. For one species, C. hamatus, sampling was carried out at three different geographic locations in the area of the Ross Sea and Weddell Sea. The results showed that the partition of the genetic variation within this species is not compatible with the hypothesis of panmixia as gene flow between populations was significantly reduced.     

Examination of Antarctic prokaryotic diversity through molecular comparisons

Prokaryotes perform key functions in Antarctic ecosystems, and knowledge of the taxonomy of Antarctic prokaryotes is a prerequisite for the transfer of information between fields of scientific inquiry. The taxonomy of prokaryotes has been greatly revised and improved due to the refinements afforded by molecular techniques such as 16S rRNA sequencing. Past inventories of Antarctic microbial diversity are difficult to reconcile with the developing, phylogenetically-based taxonomy.Antarctic prokaryotes are considerably diverse and most evolutionary groups are represented, including representatives of both Archaea and Bacteria. The diversity appears unique due to the ease with which new species can be isolated; however, that may be a result of our vastly incomplete knowledge of both Antarctic and non-Antarctic prokaryotic diversity. Use of the 16S rRNA gene as a molecular clock would suggest that the majority of Antarctic prokaryotes diverged from their nearest known non-Antarctic relatives long before a stable ice-sheet developed in Antarctica. The time of colonization (or recolonization) of Antarctic environments by individual species may have been very recent in evolutionary time scales.