Embryonic β-globin in the non-Antarctic notothenioid fish Cottoperca gobio (Bovichtidae)

The genome sequence of the channel bull blenny, Cottoperca gobio (Günther, 1861)

We present a genome assembly for Cottoperca gobio (channel bull blenny, (Günther, 1861)); Chordata; Actinopterygii (ray-finned fishes), a temperate water outgroup for Antarctic Notothenioids. The size of the genome assembly is 609 megabases, with the majority of the assembly scaffolded into 24 chromosomal pseudomolecules. Gene annotation on Ensembl of this assembly has identified 21,662 coding genes.

Molecular adaptations in haemoglobins of notothenioid fishes

Since haemoglobins of all animal species have the same haem group, differences in their properties, including oxygen affinity, electrophoretic mobility and pH sensitivity, must result from the interaction of the prosthetic group with specific amino-acid residues in the primary structure. For this reason, fish globins have been the subject of extensive studies in recent years, not only for their structural characteristics, but also because they offer the possibility to investigate the evolutionary history of these ancient molecules in marine and freshwater species living in a great variety of environmental conditions. This review summarizes the current knowledge on the structure, function and phylogeny of haemoglobins of notothenioid fishes. On the basis of crystallographic analysis, the evolution of the Root effect is analysed. Adaptation of the oxygen transport system in notothenioids seems to be based on evolutionary changes, involving levels of biological organization higher than the structure of haemoglobin. These include changes in the rate of haemoglobin synthesis or in regulation by allosteric effectors, which affect the amount of oxygen transported in blood. These factors are thought to be more important for short-term response to environmental challenges than previously believed.

The adaptation of polar fishes to climatic changes: Structure, function and phylogeny of haemoglobin

In the Antarctic, fishes of dominant suborder Notothenioidei have evolved in a unique thermal scenario. Phylogenetically related taxa of the suborder live in a wide range of latitudes, in Antarctic, sub-Antarctic and temperate oceans. Consequently, they offer a remarkable opportunity to study the physiological and biochemical characters gained and, conversely, lost during their evolutionary history. The evolutionary perspective has also been pursued by comparative studies of some features of the heme protein devoted to O(2) transport in fish living in the other polar region, the Arctic. The two polar regions differ by age and isolation. Fish living in each habitat have undergone regional constraints and fit into different evolutionary histories. The aim of this contribution is to survey the current knowledge of molecular structure, functional features, phylogeny and adaptations of the haemoglobins of fish thriving in the Antarctic, sub-Antarctic and Arctic regions (with some excursions in the temperate latitudes), in search of insights into the convergent processes evolved in response to cooling. Current climate change may disturb adaptation, calling for strategies aimed at neutralising threats to biodiversity.

Inferring evolution of fish proteins: the globin case study

Because hemoglobins (Hbs) of all animal species have the same heme group, differences in their properties, including oxygen affinity, electrophoretic mobility, and pH sensitivity, must result from the interaction of the prosthetic group with specific amino acid residues in the primary structure. For this reason, fish globins have been the object of extensive studies in the past few years, not only for their structural characteristics but also because they offer the possibility to investigate the evolutionary history of Hbs in marine and freshwater species living in a large variety of environmental conditions. For such a purpose, phylogenetic analysis of globin sequences can be combined with knowledge of the phylogenetic relationships between species. In addition, Type I functional-divergence analysis is aimed toward predicting the amino acid residues that are more likely responsible for biochemical diversification of different Hb families. These residues, mapped on the three-dimensional Hb structure, can provide insights into functional and structural divergence.

Biogeography and adaptation of Notothenioid fish: hemoglobin function and globin-gene evolution

The recognition of the important role of the polar habitats in global climate changes has awakened great interest in the evolutionary biology of polar organisms. They are exposed to strong environmental constraints, and it is important to understand how they have adapted to cope with these challenges and to what extent adaptations may be upset by current climate changes. We present an introductory overview of the evolution of the Antarctic fish fauna with emphasis on the dominant perciform sub-order Notothenioidei, as well as some specific comments on the biogeography of the three phyletically basal notothenioid families. The wealth of information on the ecology and biodiversity of the species inhabiting high-Antarctic and sub-Antarctic regions provides a necessary framework for better understanding the origin, evolution and adaptation of this unique group of fish. Notothenioidei offer opportunities for identification of the biochemical characters or the physiological traits responsible for thermal adaptation. The availability of phylogenetically related taxa in a wide range of latitudes has allowed to look into the molecular bases of environmentally driven phenotypic gain and loss of function. In the process of cold adaptation, the evolutionary trend of notothenioids has produced unique specialisations, including modification of hematological characteristics, e.g. decreased amounts and multiplicity of hemoglobins. The Antarctic family Channichthyidae (the notothenioid crown group) is devoid of hemoglobin. This loss is related to a single deletional event removing all globin genes with the exception of the inactive 3' end of adult alpha-globin. In reviewing hemoglobin structure, function and phylogeny, the evolution of the fish Root effect is analysed in detail. Adaptation of the oxygen-transport system in notothenioids seems to be based on evolutionary changes involving levels of biological organisation higher than the structure of hemoglobin.