Overwintering strategies of terrestrial invertebrates in Antarctica – the significance of flexibility in extremely seasonal environments

Antarctic terrestrial communities are characterised by their geographical isolation and the survival of extreme environmental stresses. Of particular significance to life history strategies of organisms in continental and maritime. Antarctic zones is the pronounced seasonality, with short (1-4 month) cold summers and long (8-11 month) winters. Activity and growth are largely limited to the summer period, although maintenance costs, undetectable in the short-term, may become significant over winter. Sub-Antarctic invertebrate communities experience a less rigorous regime, as climatic extremes are ameliorated by their oceanic environment, with positive mean temperatures occurring over 6-12 months. Here, year-round activity and growth of invertebrates are common. This paper considers our limited knowledge of the life histories of sub-Antarctic and Antarctic terrestrial invertebrates, to identify features correlated with seasonal and/or climatic cues. There is little evidence for diapause, although seasonal patterns of variation in cold tolerance and cryoprotectant production in direct response to desiccation and decreasing temperatures have been reported. A rapid response to feeding and growth opportunity is shown by maritime. Antarctic species, irrespective of season, although moulting does not occur over winter. Associated reduction of feeding, along with arrested growth and reproductive activity due to the low thermal energy budget over winter are probably sufficient to explain the peaks of moulting and reproduction often observed at the end of winter. Generally there is a high level of flexibility in the observed species life histories, with varying developmental duration and much overlap of generations being the norm, particularly in maritime and continental Antarctica. A formal diapause may be a disadvantage in maritime and continental Antarctic zones, as it would be erroneously triggered by severe conditions during summer. In contrast, the development of specific overwintering strategies including diapause may be unnecessary or even irrelevant in much of the sub-Antarctic, where seasonality is greatly reduced and the risk of severe of stressful environmental conditions during winter is negligible.

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