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14 results for “Antarctic icefish”
Supplementary data for: Genomics of secondarily temperate adaptation in the only non-Antarctic icefish
<p class="MsoNormal">White-blooded Antarctic icefishes are an example of extreme biological specialization both to the chronic cold of the Southern Ocean and to life without hemoglobin. As a result, icefishes display derived physiology that limits them to the cold and highly oxygenated Antarctic waters. Despite these constraints, a single icefish species, the pike icefish <em>Champsocephalus esox</em>, is presently found in temperate South American waters. To study the genetic mechanisms underlying temperate adaptation in this species, we generated chromosome-level genome assemblies of both <em>C. esox</em> and its Antarctic sister species, <em>Champsocephalus gunnari</em>. The <em>C. esox </em>genome is similar in structure and organization to that of Antarctic icefishes. However, we observe evidence of chromosomal rearrangements, some of which coincide with regions of elevated genetic divergence in pike icefish populations. Our results show several key biological pathways under selection, including genes related to the mitochondria, iron transport, and light sensing, highlighting candidates behind temperate adaptation in this species. The <em>C. esox</em> genome also shows antifreeze glycoprotein pseudogenization, likely due to relaxed selection following ancestral escape from Antarctica. While the organization of the canonical antifreeze glycoprotein locus is conserved in both <em>C. esox</em> and <em>C. gunnari</em>, both<em> </em>species show a translocation of antifreeze genes, previously unobserved in notothenioids. Our results present the first genomic characterization of a secondarily temperate notothenioid to date and serve as a basis for understanding the group's adaptive potential against a rapidly changing Antarctic environment.</p>
Cranial modularity drives phenotypic diversification and adaptive radiation of Antarctic icefishes
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Supplementary data for: Genomics of secondarily temperate adaptation in the only non-Antarctic icefish
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Data from: The loss of hemoglobin and myoglobin does not minimize oxidative stress in Antarctic icefishes
The unusual pattern of expression of hemoglobin (Hb) and myoglobin (Mb) among Antarctic notothenioid fishes provides an exceptional model system for assessing the impact of these proteins on oxidative stress. We tested the hypothesis that the lack of oxygen-binding proteins may reduce oxidative stress. Levels and activity of pro-oxidants, small-molecule and enzymatic antioxidants, and levels of oxidized lipids and proteins in liver, oxidative skeletal muscle, and heart ventricle were quantified in five species of notothenioid fishes differing in the expression of Hb and Mb. Levels of ubiquitinated proteins and rates of protein degradation by the 20S proteasome were also quantified. Although levels of oxidized proteins and lipids, ubiquitinated proteins, and antioxidants are higher in red-blooded fishes than in Hb-less icefishes in some tissues, this pattern does not persist across all tissues. Expression of Mb is not associated with oxidative damage in heart ventricle, whereas the activity of citrate synthase and contents of heme are positively correlated with oxidative damage in most tissues. Despite some tissue differences in levels of protein carbonyls among species, rates of degradation by the 20S proteasome are not markedly different, suggesting either alternative pathways for eliminating oxidized proteins or redox tone varies among species. Together, our data indicate that the loss of Hb and Mb does not correspond with a clear pattern of either reduced oxidative defense or oxidative damage.
Data from: The loss of hemoglobin and myoglobin does not minimize oxidative stress in Antarctic icefishes
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Data from: Evidence for past and present hybridization in three Antarctic icefish species provides new perspectives on an evolutionary radiation
Determining the timing, extent, and underlying causes of inter-specific 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.
Figure 5 in The complete mitochondrial genome of the mackerel icefish, Champsocephalus gunnari (Actinopterygii: Channichthyidae), with reference to the evolution of mitochondrial genomes in Antarctic notothenioids
Figure 5. Phylogenetic relationships of control regions inferred by the maximum likelihood (ML) method. Statistical support is shown on the branches: bootstrap values (above) and posterior probability (below). BI, Bayesian inference; CR, control region.
Figure 1 in The complete mitochondrial genome of the mackerel icefish, Champsocephalus gunnari (Actinopterygii: Channichthyidae), with reference to the evolution of mitochondrial genomes in Antarctic notothenioids
Figure 1. Evolution of mitochondrial genomes in Antarctic notothenioids modified from Zhuang & Cheng (2010). Abbreviations: 12S, 12S ribosomal RNA; CR, control region; Cyt b, cytochrome b; E, tRNAGlu; F, tRNAPhe; ND, nicotinamide adenine dinucleotide (reduced form) dehydrogenase; P, tRNAPro; T, tRNAThr.
Figure 4. A in The complete mitochondrial genome of the mackerel icefish, Champsocephalus gunnari (Actinopterygii: Channichthyidae), with reference to the evolution of mitochondrial genomes in Antarctic notothenioids
Figure 4. A, linear representation of three types of gene content from the partial cytochrome b (Cyt b) to 12S rRNA in the mitochondrial (mt) genome of the mackerel icefish. Black and dark grey arrows respectively represent the first and the second duplicates. The first duplicate of the type-1 genome contains full-length nicotinamide adenine dinucleotide (reduced form) dehydrogenase subunit 6 (ND6) and tRNAGlu. Type-2 contains a half-sized ND6 only. Type-3 does not contain ND6 or tRNAGlu. B, PCR amplifications for detecting ND6 and tRNAGlu in the three types of mt genome of the mackerel icefish. PCR fragments between Cyt b and control region (CR) 2 (Cyt b-CR2) and between CR2 and CR3 (CR2-CR3) contain the first and second copies of ND6, respectively. The PCR fragment between ND5 and Cyt b (ND5-Cyt b) did not contain ND6 or tRNAGlu. M, size marker. Lanes 1, 2, 7, and 10 are type-1 individuals. Lanes 3, 4, 8 and 11 are type-2 individuals. Lanes 5, 6, 9, and 12 are type-3 individuals. Abbreviations: E, tRNAGlu; F, tRNAPhe; P, tRNAPro; T, tRNAThr.
Figure 3 in The complete mitochondrial genome of the mackerel icefish, Champsocephalus gunnari (Actinopterygii: Channichthyidae), with reference to the evolution of mitochondrial genomes in Antarctic notothenioids
Figure 3. Map of the mackerel icefish mitochondrial (mt) genome as a circular diagram. The map represents the mt genome of a type-1 individual in which ND6 and tRNAGlu were transposed to a position between tRNAThr and tRNAPro flanked by intergenic spacers (UN3 and UN4), and the ND6- to -CR segment was duplicated once. Fourteen protein-coding genes, two rRNA genes, and noncoding regions are labelled with abbreviations. Twenty-four tRNA genes are shown by a one-letter amino acid code. Different codons used by each of tRNALeu and tRNASer are shown in parentheses. Genes transcribed from the heavy strand and light strand are respectively presented outside and inside the circle. Heavy- and light-strand replication origins are represented by OH and OL, respectively. Abbreviations: 12S, 12S ribosomal RNA; 16S, 16S ribosomal RNA; A, tRNAAla; ATP, ATP synthase; C, tRNACys; CO, cytochrome oxidase; Cyt b, cytochrome b; D, tRNAAsp; E, tRNAGlu; F, tRNAPhe; G, tRNAGly; H, tRNAHis; I, tRNAIle; K, tRNALys; L, tRNALeu; M, tRNAMet; N, tRNAAsn; ND, nicotiamide adenine dinucleotide (reduced form) dehydrogenase; P, tRNAPro; Q, tRNAGln; R, tRNAArg; S, tRNASer; T, tRNAThr; V, tRNAVal; W, tRNATrp; Y, tRNATyr.
Data from: Evidence for past and present hybridization in three Antarctic icefish species provides new perspectives on an evolutionary radiation
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Data from: Evolutionary suppression of erythropoiesis via the modulation of TGF-β signaling in an Antarctic icefish
The Antarctic icefish, a family (Channichthyidae) of teleosts within the perciform suborder Notothenioidei, are the only known vertebrates without oxygen-transporting haemoglobins and that are largely devoid of circulating erythrocytes. To elucidate the evo-devo mechanisms underpinning the suppressed erythropoiesis in the icefish, we conducted comparative studies on the transcriptomes and microRNAomes of the primary haematopoietic tissues between an icefish (Chionodraco hamatus) and two red-blooded notothenioids (Trematomus bernacchii and Gymnodraco acuticeps). We identified substantial remodelling of the haematopoietic programs in the icefish through which erythropoiesis is selectively suppressed. Experimental verification showed that erythropoietic suppression in the icefish may be attributable to the upregulation of TGF-β signalling, which coincides with reductions in multiple transcription factors essential for erythropoiesis and the upregulation of hundreds of microRNAs, the majority (> 80%) of which potentially target erythropoiesis regulating factors. Of the six microRNAs selected for verification, three miRNAs (miR-152, miR-1388 and miR-16b) demonstrated suppressive functions on GATA1 and ALAS2, which are two factors important for erythroid differentiation, resulting in reduced numbers of erythroids in microinjected zebra fish embryos. Codon substitution analyses of the genes of the TGF-β superfamily revealed signs of positive selection in TGF-β1 and endoglin in the lineages leading to Antarctic notothenioids. Both genes are previously known to function in erythropoietic suppression. These findings implied a general trend of erythropoietic suppression in the cold-adapted notothenioid lineages through evolutionary modulation of the multi-functional TGF-β signalling pathway. This trend is more pronounced in the haemoglobin-less icefish, which may pre-emptively hinder the otherwise defective erythroids from production.
Data from: Evolutionary suppression of erythropoiesis via the modulation of TGF-β signaling in an Antarctic icefish
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Evolutionary suppression of erythropoiesis via the modulation of TGF-β signaling in an Antarctic icefish
GEO Series GSE70113. Gymnodraco acuticeps; Trematomus bernacchii; Chionodraco hamatus. 9 samples. Type: Expression profiling by high throughput sequencing.
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