Effect of elevated temperature on membrane lipid saturation in Antarctic notothenioid fish.

Homeoviscous adaptation (HVA) is a key cellular response by which fish protect their membranes against thermal stress. We investigated evolutionary HVA (long time scale) in Antarctic and non-Antarctic fish. Membrane lipid composition was determined for four Perciformes fish: two closely related Antarctic notothenioid species (Trematomus bernacchii and Pagothenia borchgrevinki); a diversified related notothenioid Antarctic icefish (Chionodraco hamatus); and a New Zealand species (Notolabrus celidotus). The membrane lipid compositions were consistent across the three Antarctic species and these were significantly different from that of the New Zealand species. Furthermore, acclimatory HVA (short time periods with seasonal changes) was investigated to determine whether stenothermal Antarctic fish, which evolved in the cold, stable environment of the Southern Ocean, have lost the acclimatory capacity to modulate their membrane saturation states, making them vulnerable to anthropogenic global warming. We compared liver membrane lipid composition in two closely related Antarctic fish species acclimated at 0 °C (control temperature), 4 °C for a period of 14 days in T. bernacchii and 28 days for P. borchgrevinki, and 6 °C for 7 days in both species. Thermal acclimation at 4 °C did not result in changed membrane saturation states in either Antarctic species. Despite this, membrane functions were not compromised, as indicated by declining serum osmolality, implying positive compensation by enhanced hypo-osmoregulation. Increasing the temperature to 6 °C did not change the membrane lipids of P. borchgrevinki. However, in T. bernacchii, thermal acclimation at 6 °C resulted in an increase of membrane saturated fatty acids and a decline in unsaturated fatty acids. This is the first study to show a homeoviscous response to higher temperatures in an Antarctic fish, although for only one of the two species examined.

Changes in physiological responses of an Antarctic fish, the emerald rock cod (Trematomus bernacchii), following exposure to polybrominated diphenyl ethers (PBDEs).

Although polybrominated diphenyl ethers (PBDEs) have the ability to undergo long-range atmospheric transport to remote ecosystems like Antarctica, a recent study found evidence for a local source within the Antarctic. PBDEs from sewage treatment outfalls of McMurdo Station and Scott Base on Ross Island have been attributed to the high concentrations measured in emerald rock cod (Trematomus bernacchii). The potential impact of PBDEs on Antarctic fish physiology is unknown and therefore, the aim of this study was to obtain a greater understanding of physiological responses of emerald rock cod for assessing changes in ecosystem quality. A PBDE mixture (ΣPBDE 8 congeners) was administered fortnightly over 42 days and physiological changes were observed throughout this period and for a further 14 days thereafter. Changes in liver composition, molecular level changes and enzyme activities of selected detoxification-mediated and antioxidant defence markers were measured. Changes in total lipid, lipid peroxide and protein carbonyl concentrations in emerald rock cod liver were consistent with increases in nucleus surface area in the PBDE-treated groups, suggesting alterations in cellular function. Changes in the activities of selected antioxidant enzymes indirectly indicated oxidative stress, possibly resulting in the changes in liver composition. Additionally, glutathione-S-transferase (GST) activity reached its peak faster than that of ethoxyresorufin-O-deethylase (EROD), suggesting that during the early response to PBDE exposures there could be a greater involvement of GST-mediated detoxification. Thus, for at least the species examined here, protein carbonyl and lipid peroxides were useful and informative biomarkers for cellular level responses following PBDE-related exposure. Furthermore, our findings suggest that emerald rock cod exposed to PBDEs develop oxidative stress - a condition with potential consequences for fish growth, health and reproduction.

Lungfish albumin is more similar to tetrapod than to teleost albumins: purification and characterisation of albumin from the Australian lungfish, Neoceratodus forsteri.

Lobe-finned fish, particularly lungfish, are thought of as the closest extant relatives to tetrapods. Albumin, the major vertebrate plasma protein, has been well studied in tetrapods, but there exists no comparative study of the presence and characteristics of albumin in lobe-finned fish versus other vertebrates. There is a controversy over the presence of albumin in fish, although it is present in salmonids and lamprey. The presence of albumin in lungfish has also recently been documented. We identified albumin in plasma of the Australian lungfish, Neoceratodus forsteri, using a combination of agarose gel electrophoresis, [(14)C]palmitic acid binding and SDS-PAGE. Lungfish albumin was purified using DEAE-ion exchange chromatography, and has a mass of 67 kDa, is present at approximately 8 g/L in plasma and like other fish albumins, does not bind nickel. However, like tetrapod albumins, it is not glycosylated. N-terminal and internal peptide sequencing generated 101 amino acids of sequence, which showed a high degree of identity with tetrapod albumins. Despite the similarity in sequence but congruent with the evolutionary distances separating them, lungfish albumin did not cross-react with anti-chicken or anti-tuatara A albumin antisera. Lungfish albumin has characteristics more akin with tetrapod albumin and less like those of other fish.

Mother's curse: the effect of mtDNA on individual fitness and population viability.

The mitochondrial genome is considered generally to be an innocent bystander in adaptive evolution; however, there is increasing evidence that mitochondrial DNA (mtDNA) is an important contributor to viability and fecundity. Some of this evidence is now well documented, with mtDNA mutations having been shown to play a causal role in degenerative diseases, ageing, and cancer. However, most research on mtDNA has ignored the possibility that other instances exist where mtDNA mutations could have profound fitness consequences. Recent work in humans and other species now indicates that mtDNA mutations play an important role in sperm function, male fertility, and male fitness. Ironically, deleterious mtDNA mutations that affect only males, such as those that impair sperm function, will not be subject to natural selection because mitochondria are generally maternally inherited and could reach high frequencies in populations if the mutations are not disadvantageous in females. Here, we review how such mtDNA mutations might affect the viability of natural populations. We consider factors that increase or decrease the strength of the effect of mtDNA mutations on population viability and discuss what mechanisms exist to mitigate deleterious mtDNA effects.