Activity and dormancy in relation to body water and cold tolerance in a winter-active springtail (Collembola)

Abstract

Abstract. Ceratophysella sigillata (Collembola, Hypogastruridae) has a life cycle which may extend for >2 years in a temperate cli mate. It exists in two main morphs, a winter-active morph and a summer-dormant morph in central European forests. The winteractive morph often occurs in large aggregations, wandering on leaf litter and snow surfaces and climbing on tree trunks. The summer-dormant morph is found in the upper soil layers of the forest floor. The cryobiology of the two morphs, sampled from a population near Bern in Switzerland, was examined using Differential Scanning Calorimetry to elucidate the roles of body water and the cold tolerance of individual springtails. Mean (SD) live weights were 62 ± 16 and 17 ± 6 pg for winter and summer individuals, respectively. Winter-active springtails, which were two feeding instars older than summer-dormant individuals, were significantly heavier (by up to 4 times), but contained less water (48% of fresh weight [or 0.9 g g-1 dry weight]) compared with summer-dormant animals (70% of fresh weight [or 2.5 g g-1 dry weight]). Summer-dormant animals had a slightly greater supercooling capacity (mean (SD) -16 ± 6°C) compared with winter-active individuals (-12 ± 3°C), and they also contained significantly larger amounts of both total body water and osmotically inactive (unfrozen) water. In the summer morph, the unfrozen fraction was 26%, compared to 11% in the winter morph. The ratio of osmotically inactive to osmotically active (freezable) water was 1:1.7 (summer) and 1 : 3.3 (win ter); thus unfrozen water constituted 59% of the total body water during summer compared with only 30% in winter. Small, but sig nificant, levels of thermal hysteresis were detected in the winter-active morph (0.15°C) and in summer-dormant forms (0.05°C), which would not confer protection from freezing. However, the presence of antifreeze proteins may prevent ice crystal growth when feeding on algae with associated ice crystals during winter. It is hypothesised that in summer animals a small decrease in freezable water results in a large increase in haemolymph osmolality, thereby reducing the vapour pressure gradient between the springtail and the surrounding air. A similar decrease in freezable water in winter animals will not have such a large effect. The transfer of free water into the osmotically inactive state is a possible mechanism for increasing drought survival in the summer-dormant morph. The ecophysiological differences between the summer and winter forms of C. sigillata are discussed in relation to its population ecology and survival.

Cold tolerance in terrestrial invertebrates inhabiting subterranean habitats

“…2000; Block, 2002;Block & Zettel, 2003;Ansart & Vernon, 2003;Sinclair et al, 2003;Hodkova & Hodek, 2004;Danks, 2006;Lagerspetz & Vainio, 2006;Hawes & Bale, 2007;Bowler & Terblanche, 2008;MacMillan & Sinclair, 2011;Vesala & Hoikkala, 2011). The stepwise 1°C-graded arrangement of our experiment does not allow precise determination of the LLTs; the real values may be, on average, about 0.5°C higher.…”

Key themes in the study of seasonal adaptations in insects I. Patterns of cold hardiness

“…These themes have been reinforced by later work (e.g. Block, 1996Block, , 2002Danks, 2000a;Bayley et al, 2001;Block and Zettel, 2003), showing that there is indeed a wide range of adaptations to desicca-tion, as well as interactions or coincident adaptations with cold hardiness. As might be expected, the extent of the linkages varies among species and among habitats (e.g.…”

“…Not surprisingly, water available for such removal is reduced in many insects prior to the winter, reported as a reduction in free water or as an increase in "bound water" or "unfreezable water" (e.g. Block, 2002;Block and Zettel, 2003;and see Wolfe et al, 2002). Such dehydration is not always part of the cold-hardiness mechanism, but it does enhance cold hardiness in many species.…”

Importance of the Body Water Management for Winter Cold Survival of the European Corn BorerOstrinia NubilalisHübn. (Lepidoptera: Pyralidae)

“…A Differential Scanning Calorimeter (DSC820, MettlerToledo) was utilized in this study to examine thermal changes in fat body and hemolymph subjected to cooling and warming programmes (3).…”

“…In cryobiology bound water equates with unfrozen water and is osmotically inactive (OI), whilst free water is osmotically active (OA) (2). Thermal analysis techniques are widely used in the studies of cold resistance and water dynamics of invertebrates (3). Apart from the promotion of supercooling, the quantity of dissolved solutes, usually polyhydric alcohols and sugars, determine the form of water (free or bound) as well as its distribution within the cell/body.…”