Life cycle strategies in two Antarctic Collembola

The significance of the moult cycle to cold tolerance in the Antarctic collembolan Cryptopygus antarcticus

Research into the ecophysiology of arthropod cold tolerance has largely focussed on those parts of the year and/or the life cycle in which cold stress is most likely to be experienced, resulting in an emphasis on studies of the preparation for and survival in the overwintering state. However, the non-feeding stage of the moult cycle also gives rise to a period of increased cold hardiness in some microarthropods and, as a consequence, a proportion of the field population is cold tolerant even during the summer active period. In the case of the common Antarctic springtail Cryptopygus antarcticus, the proportion of time spent in this non-feeding stage is extended disproportionately relative to the feeding stage as temperature is reduced. As a result, the proportion of the population in a cold tolerant state, with low supercooling points (SCPs), increases at lower temperatures. We found that, at 5 degrees C, about 37% of the population are involved in ecdysis and exhibit low SCPs. At 2 degrees C this figure increased to 50% and, at 0 degrees C, we estimate that 80% of the population will have increased cold hardiness as a result of a prolonged non-feeding, premoult period. Thus, as part of the suite of life history and ecophysiological features that enable this Antarctic springtail to survive in its hostile environment, it appears that it can take advantage of and extend the use of a pre-existing characteristic inherent within the moulting cycle.

Environmental constraints on life histories in Antarctic ecosystems: tempos, timings and predictability

Knowledge of Antarctic biotas and environments has increased dramatically in recent years. There has also been a rapid increase in the use of novel technologies. Despite this, some fundamental aspects of environmental control that structure physiological, ecological and life-history traits in Antarctic organisms have received little attention. Possibly the most important of these is the timing and availability of resources, and the way in which this dictates the tempo or pace of life. The clearest view of this effect comes from comparisons of species living in different habitats. Here, we (i) show that the timing and extent of resource availability, from nutrients to colonisable space, differ across Antarctic marine, intertidal and terrestrial habitats, and (ii) illustrate that these differences affect the rate at which organisms function. Consequently, there are many dramatic biological differences between organisms that live as little as 10 m apart, but have gaping voids between them ecologically. Identifying the effects of environmental timing and predictability requires detailed analysis in a wide context, where Antarctic terrestrial and marine ecosystems are at one extreme of the continuum of available environments for many characteristics including temperature, ice cover and seasonality. Anthropocentrically, Antarctica is harsh and as might be expected terrestrial animal and plant diversity and biomass are restricted. By contrast, Antarctic marine biotas are rich and diverse, and several phyla are represented at levels greater than global averages. There has been much debate on the relative importance of various physical factors that structure the characteristics of Antarctic biotas. This is especially so for temperature and seasonality, and their effects on physiology, life history and biodiversity. More recently, habitat age and persistence through previous ice maxima have been identified as key factors dictating biodiversity and endemism. Modern molecular methods have also recently been incorporated into many traditional areas of polar biology. Environmental predictability dictates many of the biological characters seen in all of these areas of Antarctic research.

Responses of terrestrial plants and invertebrates to environmental change at high latitudes

Many invertebrates show flexibility in their life cycles and are likely to respond to changes in climate as they have in the past. However, changes in temperature and photoperiod may disturb the life cycles of some existing polar invertebrates while continuing to constrain the polewards migration of more temperate species. Higher plants are likely to have higher productivity as temperatures and atmospheric CO 2 levels increase but this productivity will be reduced by exposure to increasing UV-B radiation. Higher plants migrate more slowly than the rate at which climate is predicted to change and many species will be trapped in supra-optimal climates. Both mosses and lichens can migrate faster than higher plants, propagules of non-polar species already reaching the Antarctic, but they have fewer mechanisms of responding to changing environments. Polar vegetation and ecosystems provide feedback to the climate system: positive feedbacks are associated with decreases in reflectivity and increased carbon emissions from warm ing soils. In the Antarctic, feedback and responses to environmental change will be smaller than in the Arctic because of the less responsive cryptogams which dominate the Antarctic, the paucity of Antarctic soils, and geographical barriers to plant and invertebrate migrations.