Abstract: Rats introduced on islands can affect ecosystem structure and function by feeding on terrestrial plants and both marine and terrestrial animals. The diet and trophic position of Rattus rattus introduced on Ile de la Possession (Iles Crozet) was assessed from two sites, according to the presence or absence of a king penguin colony. We used three complementary assays: macroanalyses of the stomach, faecal microhistology, and stable isotope analyses of 15N/13C in liver. Near the rookery, spermatophytes contributed on average 50% (confidential interval: 2375) to the diet based on isotopes, mainly consisting in reproductive parts of Poa spp., Agrostis magellanica, and Cerastium fontanum identified in faeces. Terrestrial animal preys were represented by insects that contributed 25% (056) in isotopes, dominated in faeces by caterpillars of Pringleophaga spp. and adult weevils. Bird remains were found in faeces, forming 18% (630) of isotopes. Terrestrial earthworms contributed to 7% (021), with chaetae observed in faeces. On the other site, spermatophytes represented 62% (5173) of assimilated food in rats livers, mainly formed by Poaceae and Acaena magellanica, insects by caterpillars [24% (1039)], and terrestrial earthworms [13% (223)]. Our results suggest that rats, which were found at the top of terrestrial food chains, may have a direct role on a such simplified ecosystem, by preying on the most abundant and largest body-sized terrestrial invertebrates,e.g. the keystone species Pringleophaga spp., and by feeding on both reproductive and vegetative parts of autochthonous and introduced plants. The discrepancies and usefulness of employing both isotopes and faecal analyses are discussed.

Abstract: The Falklands mullet, Eleginops maclovinus , is the only modern representative of the Sub-Antarctic family Eleginopidae, suborder Notothenioidei. Based on specimens from the Falkland Islands/Islas Malvinas, the Magellan Straits, and the southern coast of Chile, we have established the specific karyotype by conventional cytogenetic methods and have mapped the chromosomal loci of the ribosomal genes by fluorescence in situ hybridization (FISH). With respect to the basal notothenioid family Bovichtidae and to the hypothetical basal condition of the suborder (diploid number = 48, fundamental number = 48), E. maclovinus displays a slightly derived karyotype (diploid number = 48, fundamental number = 54). In contrast to the bovichtids, the 45S and 5S ribosomal DNAs are co-localized to a single chromosome pair. Condensation of the ribosomal genes to a single locus is likely to represent an intermediate stage in the evolution of notothenioid karyology. Features unique to E. maclovinus (e.g., morphology of its large, rDNA-bearing chromosome pair) probably result from divergence during the long evolutionary isolation of the family.

Abstract: Many animals that possess a gizzard swallow stones or sandy grit, supposedly to aid in the mechanical breakdown of food. While this has been well documented in the literature, our study is the first to report the presence of stones in the gizzard of king penguin chicks. We found stones, so called gastroliths, in the pyloric region of the gizzard, the part of the digestive tract that is specialised for the mechanical breakdown of food. Stones were already present in the gizzard of chicks and, hence, during the first year of the life of king penguins, which is spent on land. Some chicks were found to have more than 130 stones (0.522 mm in size) in their gizzard. The gastroliths we found in king penguins are of the same geological origin as rocks present at the colony, which suggests that birds swallowed them there. The functional role of gastroliths in penguin chicks and adults is still unknown. We discuss the potential roles that these gastroliths might play in king penguins (i.e. aid in digestion, buoyancy control during foraging at sea, adaptation to fasting).

Abstract: Fatty acid (FA) and fatty alcohol (FAlc) compositions of both total lipid and neutral lipid fractions were studied for five myctophid species sampled in Kerguelen waters. Both qualitative and quantitative FA signature analyses were then performed to investigate their diet over longer time scales than the conventional stomach content analysis. Regarding their lipid class, FA and FAlc compositions, the five species could be discriminated into two groups: wax-ester-rich species ( Electrona antarctica , Krefftichthys anderssoni ) characterised by large amounts of monounsaturated FAs (>73% of total FAs) and triacylglycerol-rich species ( Electrona carlsbergi , Gymnoscopelus nicholsi , Protomyctophum bolini ) with major amounts of saturated and monounsaturated FAs (>29 and >46% of total FAs, respectively). Qualitative and quantitative FA analyses showed that K. anderssoni mainly preyed upon copepods, E. antarctica upon copepods and more euphausiids and P. bolini and E. carlsbergi mainly upon euphausiids with some copepods, while G. nicholsi had a more diverse diet. This study shows the usefulness of quantitative statistical analysis to determine the diet of Antarctic and sub-Antarctic predators and stresses the need of increasing the lipid and FA analyses of more zooplanktonic and micro-nektonic marine species.