Habitat phenotyping of two sub-Antarctic flies by metabolic fingerprinting: evidence for a species outside its home?

Metabolic fingerprinting can elucidate rearrangements of metabolic networks in organisms exposed to various environmental conditions. Maintenance of organismal performance occurs by alterations in metabolic fluxes and pathways, resulting in habitat-specific metabolic signatures. Several insects of sub-Antarctic Islands, including the wingless flies Anatalanta aptera and Calycopteryx moseleyi, are exposed to saline organic matter accumulated along littoral margins. However, C. moseleyi has long been considered restricted to a habitat of lower salinity, the Kerguelen cabbage. High C. moseleyi densities identified in saline decaying seaweeds are intriguing, and may involve osmoregulatory adjustments including accumulation of osmoprotectants. In the present work, we examined quantitative metabotypes (metabolic phenotypes) among wild C. moseleyi individuals from seaweeds versus non-saline Kerguelen cabbages. They were compared to metabotypes from wild A. aptera, a common fly on seaweed. Statistical procedures designed to magnify between-class differences failed to clearly separate C. moseleyi metabotypes from cabbage and seaweed, despite contrasted morphotypes, diets, and salinities. A. aptera exhibited higher glycerol, inositol, trehalose, and other osmoprotectants concentrations that may enhance its performance under saline environments. Seaweed may represent a secondary niche in C. moseleyi, promoted by the marked reduction in Kerguelen cabbage frequency subsequent to climate change, and herbivorous pressures caused by rabbit invasion.

Starvation resistance and effects of diet on energy reserves in a predatory ground beetle (Merizodus soledadinus; Carabidae) invading the Kerguelen Islands.

The relationship between nutritional requirements and the availability or quality of food is a prime parameter in determining the geographical expansion of invasive insects. At the sub-Antarctic Kerguelen Islands, the invasive ground beetle Merizodus soledadinus becomes the main invertebrate predator when it colonizes new habitats, leading to the local extinction of native fly species. Such changes in the structure of prey communities may alter the energy management (storage and expenditure) of this predator. In this species, we monitored survival and body mass during food deprivation, in addition to evaluating the effects of two distinct diets (maggots versus enchytraeids) on the consumption and restoration of body reserves (sugars and triglycerides). We found that adults can starve for more than 60 days, and feed every 3.76 days on average when food is available. We recorded higher predation rates on maggots, associated with steeper body mass variations, compared to enchytraeids. Sugars and triglycerides were significantly consumed during food deprivation and restored after refeeding, but varied similarly among individuals supplied on the distinct diets. Other parameters may determine the food preferences observed, such as salt content in prey tissues, because M. soledadinus mainly feeds in hypersaline foreshore habitats, and may limit the consumption of osmotic conformers.

Life cycle of the tick Ixodes uriae in penguin colonies: relationships with host breeding activity.

A survey of the temporal pattern of population structure and feeding activity of the seabird tick Ixodes uriae was conducted for the first time in two host species colonies: King penguin (Aptenodytes patagonicus halli) and Macaroni penguin (Eudyptes chrysolophus chrysolophus). The life cycle of the tick was investigated over 3 years in a King penguin colony and 2 years in a Macaroni penguin colony at Possession Island (Crozet Archipelago). There was a marked seasonal feeding activity pattern of ticks in both host species, connected with the presence of birds during the breeding season. Although the King penguin colonies were occupied throughout the year by birds, the favourable period for engorgement was limited to 3.5-4.5 months, and almost all the ticks overwintered in the unengorged state. Consequently, I. uriae probably completed its life cycle over 3 years in King penguin colonies. In contrast, this life cycle could be shortened to 2 years in Macaroni penguin colonies, as a result of a different timetable of the presence of birds for breeding and moulting. The relationships between such plasticity and the host behaviour and subantarctic climatic conditions are discussed.

Azorella selago Hook. used to estimate glacier fluctuations and climatic history in the Kerguelen Islands over the last two centuries.

Climatic variations over the two last centuries are well known for the northern hemisphere, but very little information is available for subantarctic islands. In this paper, we combined geomorphological observations and a new biological dating technique to propose a reconstruction of the cool and warm events in the Kerguelen Islands during the last two centuries. The usual dating methods, such as dendrochonology or C14 dating, are not applicable on Kerguelen. Therefore, the radial growth ofAzorella selago Hook., a cushion-forming Umbelliferae species, was used to estimate the absolute age of deglaciated areas. Glacial margins in the vicinity of the Glacier Ampère constitute the most complete chronosequence studied in this part of the world and illustrate seven warming-cooling cycles. This new dating technique is validated by the close relationship between the calculated ages of these climatic events and the results of several studies in other circumantarctic regions. The Glacier Ampère reached its maximum extent at the end of the eighteenth century. Since 1799, two discrete phases may be distinguished: the first period (1799-1965) is characterized by small glacier fluctuations (1 km retreat overall) whereas in the second period (1966 to the present), the retreat is much more rapid (about 3 km). It seems that the current dramatic glacial retreat on Kerguelen is related to a major change in the climate and could illustrate a more general southern hemispheric pattern of glacial fluctuations.