Antarctic ecosystems in transition - life between stresses and opportunities.

Important findings from the second decade of the 21st century on the impact of environmental change on biological processes in the Antarctic were synthesised by 26 international experts. Ten key messages emerged that have stakeholder-relevance and/or a high impact for the scientific community. They address (i) altered biogeochemical cycles, (ii) ocean acidification, (iii) climate change hotspots, (iv) unexpected dynamism in seabed-dwelling populations, (v) spatial range shifts, (vi) adaptation and thermal resilience, (vii) sea ice related biological fluctuations, (viii) pollution, (ix) endangered terrestrial endemism and (x) the discovery of unknown habitats.

Quantification of neurons in the olfactory bulb of the catsharks Scyliorhinus canicula (Linnaeus, 1758) and Galeus melastomus (Rafinesque, 1810).

In vertebrates, the olfactory bulb (OB) is the zone of the brain devoted to receiving the olfactory stimuli. The size of the OB relative to the size of the brain has been positively correlated to a good olfactory capability but, recently, this correlation was questioned after new investigation techniques were developed. Among them, the isotropic fractionator allows to estimate the number of neurons and non-neurons in a given portion of nervous tissue.

High mercury levels in Antarctic toothfish Dissostichus mawsoni from the Southwest Pacific sector of the Southern Ocean.

Mercury is a bioaccumulating toxic pollutant which can reach humans through the consumption of contaminated food (e.g. marine fish).

Cytogenetic characterization of the Antarctic silverfish Pleuragramma antarctica (Boulenger 1902) through analysis of mitotic chromosomes from early larvae.

This paper describes the cytogenetic features of the Antarctic silverfish Pleuragramma antarctica (Boulenger 1902), a keystone species of the Antarctic coastal marine ecosystem. Conventional cytogenetic analyses and physical mapping of repetitive DNA sequences were performed on metaphase plates obtained through direct chromosome preparation from P. antarctica early larvae.

Secondary Folds Contribute Significantly to the Total Surface Area in the Olfactory Organ of Chondrichthyes.

The olfactory organ of Chondrichthyes is characterized by a central support with several lamellae covered by a sensory olfactory epithelium. Although secondary folds are present on the lamellae in all the chondrichthyan species analyzed to date, their shape and size have not been described. We here analyze the olfactory organ of 13 elasmobranch and 1 holocephalan species, describe the shape of the secondary folds and evaluate how they contribute to the epithelial surface area.

Legacy persistent organic pollutants including PBDEs in the trophic web of the Ross Sea (Antarctica).

The ecological features of the Ross Sea trophic web are peculiar and different from other polar food webs, with respect to the use of habitat and species interactions; due to its ecosystem integrity, it is the world's largest Marine Protected Area, established in 2016. Polar organisms are reported to bioaccumulate lipophilic contaminant, viz persistent organic pollutants (POPs). Legacy POPs and flame retardants (polybrominated diphenyl ethers, PBDEs) were studied in key species of the Ross Sea (Euphausia superba, Pleuragramma antarctica) and their predators (Dissostichus mawsoni, Pygoscelis adeliae, Aptenodytes forsteri, Catharacta maccormicki, Leptonychotes weddellii).

Clarification of the Terminology of the Olfactory Lamellae in Chondrichthyes.

Several papers regard the anatomy of the peripheral olfactory organ, the olfactory rosette, in the class of Chondrichtyes. The complex shape of this organ and the differences among species give clues to functional, evolutionary, and ecological observations; data on a larger number of species are needed in order to have a more complete insight. The rosette is made up of a central support and of numerous lamellae, which are lined by the sensory epithelium.

Gross anatomy and histology of the olfactory rosette of the shark Heptranchias perlo.

Sharks belonging to the family Hexanchidae have six or seven gill slits, unlike all other elasmobranchs, which have five gill slits. Their olfactory organs have a round shape, which is common for holocephalans, but not for elasmobranchs. Thus, the shape of the olfactory organ represents a further, less striking, peculiarity of this family among elasmobranchs.

Evolution in an extreme environment: developmental biases and phenotypic integration in the adaptive radiation of antarctic notothenioids.

Background: Over the past 40 million years water temperatures have dramatically dropped in the Southern Ocean, which has led to the local extinction of most nearshore fish lineages. The evolution of antifreeze glycoproteins in notothenioids, however, enabled these ancestrally benthic fishes to survive and adapt as temperatures reached the freezing point of seawater (-1.86 °C).

First Description of a Palatal Organ in Chimaera monstrosa (Chondrichthyes, Holocephali).

Chimaeroid fishes are the only extant Holocephali, a subclass of Chondrichthyes. We describe for the first time a well evidenced structure localized in the palate of the chimaeroid Chimaera monstrosa, here named a palatal organ (PO). Attention has been paid to the holocephalan head morphology, but there has been no mention of this particular organ in the literature.

A demonstration of nesting in two antarctic icefish (genus Chionodraco) using a fin dimorphism analysis and ex situ videos.

Visual observations and videos of Chionodraco hamatus icefish at the "Acquario di Genova" and histological analyses of congeneric species C. hamatus and C. rastrospinosus adults sampled in the field provided new anatomical and behavioral information on the reproductive biology of these white blooded species that are endemic to the High-Antarctic region.

First detection of taste buds in a chimaeroid fish (Chondrichthyes: Holocephali) and their Gαi-like immunoreactivity.

The mucosa covering the tongue of the Chimaera monstrosa has been investigated with histological and immunohistochemical methods allowing to describe, for the first time, gustatory structures (taste buds) in this subclass of cartilaginous fish. G-protein-alpha-subunit-inhibitory-like (Gαi-like) immunoreactivity has been detected in the taste buds of C. monstrosa, as described in other vertebrates.

Neuronal nitric oxide synthase (nNOS) immunoreactivity in the olfactory system of a cartilaginous fish.

Nitric oxide is a regulative molecule with important roles in the olfactory system of vertebrates. Chondrichtyans have a key position in vertebrate evolution and nothing is known about nitric oxide in their olfactory system. Aim of this work was to investigate the neuronal nitric oxide synthase (nNOS) immunoreactivity in the olfactory system of the shark Scyliorhinus canicula.

Cell proliferation and apoptosis in the olfactory epithelium of the shark Scyliorhinus canicula.

To date, no study has been published on cell renewal in the olfactory epithelium of Chondrichthyes. Our work aimed at detecting proliferating cells (by Proliferating Cell Nuclear Antigen - PCNA immunohistochemistry) and apoptotic cells (by terminal uridine deoxynucleotidyl transferase nick end labeling method) in the olfactory epithelium of the shark Scyliorhinus canicula. PCNA immunoreactivity and mitotic figures were localized almost exclusively at the basal and apical thirds of the epithelial thickness.

First evidence of a leptin-like peptide in a cartilaginous fish.

Leptin is a hormone involved in food intake. Although leptin is evolutionarily conserved, no studies have investigated its presence in cartilaginous fish. Here, we report the presence of leptin-like immunoreactivity in the gastro-intestinal tract and liver of the cartilaginous fish Scyliorhinus canicula using western blot and immunohistochemical analyses.

G protein alpha subunits in the olfactory epithelium of the holocephalan fish Chimaera monstrosa.

Receptor neurons in the olfactory and vomeronasal epithelia of vertebrates have dendritic specialization that is correlated to the receptor gene family they express and the G protein coupled with that receptor (in particular the G protein alpha subunit). There are not very many data in the literature about the morphological and molecular features of the olfactory epithelium of Chondrichthyes. In this work, the presence and distribution of different types of G protein alpha subunits (Galpha(o), Galpha(q) and Galpha(olf)) were investigated in the olfactory epithelium of the holocephalan Chimaera monstrosa using immunohistochemistry.

Molecular pedomorphism underlies craniofacial skeletal evolution in Antarctic notothenioid fishes.

Background: Pedomorphism is the retention of ancestrally juvenile traits by adults in a descendant taxon. Despite its importance for evolutionary change, there are few examples of a molecular basis for this phenomenon. Notothenioids represent one of the best described species flocks among marine fishes, but their diversity is currently threatened by the rapidly changing Antarctic climate.

First detection of neuropeptide Y (NPY)-like immunoreactivity in the lateral line: presence and distribution in the neuromasts of the Antarctic notothenioid fish Trematomus bernacchii.

The mechanosensory lateral line (LL) is involved in many fish and amphibian behaviors, however little is known about the molecules involved in the signal transmission. Neuropeptide Y (NPY) has a number of functions in vertebrate physiology and also plays important roles in different sensory systems. The Antarctic nototheniods are a monophyletic radiation of fishes that have evolved under the extreme environmental conditions of low light and cold, where non-visual sensory structures, such as LL, are of importance.

GnRH immunodetection in the brain of the holocephalan fish Chimaera monstrosa L.: correlation to oocyte maturation.

Chimera monstrosa (rabbit fish) like other holocephalans is a rare, delicate deep sea fish. Owing to the difficulty of sampling individuals in good shape, there is a paucity of information available on the morphology and physiology of this species especially concerning reproduction. In holocephalans, a hypothalamus-pituitary-gonadal axis has been postulated and a GnRH molecule identical to cGnRH II has been identified.

First detection of olfactory marker protein (OMP) immunoreactivity in the olfactory epithelium of a cartilaginous fish.

Olfactory marker protein (OMP) is a protein expressed in the mature olfactory and vomeronasal neurons of many vertebrates, such as mammals, amphibians and bony fishes. Aim of this work was to investigate the OMP expression in the olfactory epithelium of the shark Scyliorhinus canicula (Linnaeus, 1758), by immunohistochemistry (IHC). Immunoreactivity was detected in the olfactory receptor neurons, in the crypt neurons and in the nerve fibers below the epithelium.

Observations of crypt neuron-like cells in the olfactory epithelium of a cartilaginous fish.

A new receptor neuron (RN) type was recently described in bony fish olfactory epithelium (OE): the crypt receptor neuron. This name is due to its main feature: the presence, at the apical part, of a deep invagination into which cilia protrude. The presence of this receptor neuron type is well documented in different species of bony fishes but it has never been described in cartilaginous fishes.