No abstract

Although several invertebrates have been introduced by Man into the Antarctic, no holometabolous insects have survived to colonize terrestrial habitats successfully. Data are presented on the survival of populations of a chironomid midge, together with an enchytraeid worm, for 17 years in a maritime Antarctic site at Signy Island, South Orkney Islands. Both species are thought to have been introduced on plant material transplanted from either South Georgia or the Falkland Islands or both in 1967. Population densities average 25718m‐2 for the dipteran larvae and 3243 m‐2 for the worms. Successful completion of the midge's life cycle was indicated by emergence of brachypterous adults and oviposition (the population is parthenogenetic with only females present). Although both taxa are capable of supercooling to between ‐13 and ‐26°C, this capacity may not be sufficient in a severe winter to avoid lethal freezing. Four potential cryoprotectants were found in insect extracts, but in concentrations (< 1 % fresh weight) unlikely to influence cold hardiness. Both invertebrates appear to be pre‐adapted for survival in much harsher conditions than they normally experience, by the extension of existing physiological mechanisms. It is concluded that the main limitations to invertebrate colonization of suitable Antarctic land areas by soil‐dwelling species are geographical.

1. Populations of two coexisting Antarctic Collembola were studied in the field and under constant conditions in the laboratory to determine their life cycles and to compare their energy utilisation. 2. In the field Parisotoma octooculata completes three to four moults during summer, overwintering either in the egg stage or in the fourth or fifth instars. Maturity is reached in the second year, with synchronous oviposition and hatching. Cryptopygus antarcticus has many overlapping generations, maturity is achieved in the third year and oviposition and hatching take place throughout the year. 3. In the laboratory P. octooculata has a faster rate of growth than C. antarcticus under constant conditions of temperature and humidity. Analysis of gut contents showed that the two species overlapped in their food range; the faster growth of P. octooculata being achieved by a faster consumption rate, since the two species had similar assimilation and production efficiencies. 4. The slower growth rate of C. antarcticus may not result from limited food availability, but from a better life cycle strategy for unpredictable environmental conditions. P. octooculata, which shows features more characteristic of temperate Collembola, may be a more recent Antarctic colonist.

The normal dissolved oxygen patterns in certain temporary heterotophic pools in southeastern Louisiana are characterizd by relatively high values after initial flooding followed by a gradual decline to as low as 10% saturation as the pond ages. Laboratory delimitation of lethal oxygen thresholds for several characteristic temporary pond invertebrates revealed LD 50's of 0.1—0.4 ppm under test conditions. An unusual 8—day period of complete subsurface oxygen depletion during summer flooding in one such pond is described. Except for the conchostracans, there was little adverse effet on the macrofauna. This is attributed to the seeking of the partly oxygenated surface layer of the pond by the animals.