SUMMARY: The relative importance of freezing tolerance and cryoprotective dehydration in the Antarctic nematode Panagrolaimus davidi has been investigated. If nucleation of the medium is initiated at a high subzero temperature (-1°C), the nematodes do not freeze but dehydrate. This effect occurs in deionised water, indicating that the loss of water is driven by the difference in vapour pressure of ice and supercooled water at the same temperature. If the nematodes are held above their nucleation temperature for a sufficient time, or are cooled slowly, enough water is lost to prevent freezing (cryoprotective dehydration). However, if the medium is nucleated at lower temperatures or if the sample is cooled at a faster cooling rate, the nematodes freeze and can survive intracellular ice formation. P. davidi thus has a variety of mechanisms that ensure its survival in its harsh terrestrial Antarctic habitat.

Circum-Antarctic waters harbour a rare example of a marine species flock – the Notothenioid fish, most species of which are restricted to the continental shelf. It remains an open question as to how they survived Pleistocene climatic fluctuations characterised by repeated advances of continental glaciers as far as the shelf break that probably resulted in a loss of habitat for benthic organisms. Pelagic ecosystems, on the other hand, might have flourished during glacial maxima due to the northward expansion of Antarctic polar waters. In order to better understand the role of ecological traits in Quaternary climatic fluctuations, we performed demographic analyses of populations of four fish species from the tribe Trematominae, including both fully benthic and pelagic species using the mitochondrial cytochrome b gene and an intron from the nuclear S7 gene.

To determine if an Antarctic species repairs DNA at rates equivalent to warmer water equivalents, we examined repair of UV-damaged DNA in echinoid embryos and larvae. DNA repair by photoreactivation was compared in three species Sterechinus neumayeri (Antarctica), Evechinus chloroticus (New Zealand) and Diadema setosum (Tropical Australia) spanning a latitudinal gradient from polar (77.86°S) to tropical (19.25°S) environments. We compared rates of photoreactivation as a function of ambient and experimental temperature in all three species, and rates of photoreactivation as a function of embryonic developmental stage in Sterechinus. DNA damage was quantified from cyclobutane pyrimidine dimer (CPD) concentrations and rates of abnormal embryonic development. This study established that in the three species and in three developmental stages of Sterechinus, photoreactivation was the primary means of removing CPDs, was effective in repairing all CPDs in less than 24 h, and promoted significantly higher rates of normal development in UV-exposed embryos. CPD photorepair rate constant (k) in echinoid embryos ranged from 0.33 to 1.25 h^-1, equating to a time to 50% repair of between 0.6 and 2.1 h and time to 90%repair between 3.6 and 13.6 h. We observed that experimental temperature influenced photoreactivation rate. In Diadema plutei, the photoreactivation rate constant increased from k=0.58 h^-1 to 1.25 h^-1, with a Q₁₀=2.15 between 22°C and 32°C. When compared among the three species across experimental temperatures (-1.9 to 32°C), photoreactivation rates vary with a Q₁₀=1.39. Photoreactivation rates were examined in three developmental stages of Sterechinus embryos, and while not significantly different, repair rates tended to be higher in the younger blastula and gastrula stages compared with later stage embryos. We concluded that photoreactivation is active in the Antarctic Sterechinus, but at a significantly slower (non-temperature compensated) rate. The low level of temperature compensation in photoreactivation may be one explanation for the relatively high sensitivity of Antarctic embryos to UV-R in comparison with non-Antarctic equivalents.