Ecologically realistic modalities in arthropod supercooling point distributions

Abstract

Abstract. Modality in the supercooling points of cold tolerant but freezing intolerant terrestrial arthropods has proved a pragmatically reliable means of distinguishing between summer and winter cold hardiness in such species. This paper proposes an ecologically realistic method of modal analysis which may either be used in lieu of the traditional separation of supercooling points into "high" and "low" groups, or as a complementary assessment of the risk of freezing mortality. Instead of a posteriori determinations of modal break points, animal supercooling points are assigned a priori to one of four categories of cold hardiness: (1) summer coldhardy; (2) semi-cold-hardy; (3) cold-hardy; and (4) winter cold-hardy. Each category is identified by the temperature range within which arthropods can be expected to freeze. The temperature ranges assigned to each category are based on a conservative, but realistic, assessment of the temperatures at which animals can be expected to freeze at a given point in the season. The approach has greater discriminatory power than traditional bimodal descriptors (i.e."summer" and "winter" cold-hardy), as well as allowing animal supercooling points to be related to the temperatures they actually experience in their habitats. Thus, for example, animals considered "summer" cold-hardy according to conventional analysis may actually be "semi-cold-hardy" with supercooling points well within the safety margin of minimum ambient temperatures.

Physiological ecology of overwintering in hatchling turtles

“…Indeed, some reports of freeze tolerance in invertebrates (Paukstis et al, '96;Ansart et al, 2001;Cook, 2004), amphibians (Pasanen and Karhapää, '97;Croes and Thomas, 2000;Steiner et al, 2000), and reptiles (Claussen et al, '90;Andersson and Johansson, 2001;Burke et al, 2002) are based on experiments in which subjects have survived a measure of internal ice formation, but the tolerance is limited to superficial freezing over very brief exposures to relatively high temperatures. Compounding this problem, some authors have endeavored to catalogue various degrees of cold hardiness, including subcategories of freeze tolerance (Bale, '93, '96;Sinclair, '99;Nedved, 2000;Vernon and Vannier, 2002;Voituron et al, 2003;Hawes et al, 2006). These constructs, which have generated a litany of confounding idioms, including the oxymoron ''partial freeze tolerance,'' have done little to advance our understanding of freeze tolerance as a natural survival adaptation.…”

Temporal resolution of cold acclimation and de‐acclimation in the Antarctic collembolan,Cryptopygus antarcticus

“…Rapid changes in cold hardiness are not really a digital response because the transition between winter and summer modes is a discrete process involving a transitional state of ‘semicold hardiness’ ( sensu Hawes et al ., 2006a). However, in this species, the switch between modes, when it occurs, is nonetheless very rapid; it is not evident at lower temporal resolutions, nor indeed do animals remain ‘transitional’ for any longer than it takes to acquire their new mode of cold hardiness (i.e.…”

“…Although the cues governing the shifts between these modes at seasonal timescales have been studied extensively (Sømme & Block, 1982; Cannon, 1983; Cannon, 1987; Worland & Lukešová, 2000), recent investigations into its summer cryoprotection levels have highlighted its ability to change its cold tolerance at diurnal time‐scales (Worland & Convey, 2001). However, unlike most other Antarctic arthropods (Hawes et al ., 2006a), C. antarcticus shows little obvious evidence of a ‘transitional’/‘semicold‐hardy’ state between its modes of cold hardiness; individuals appear to ‘switch’ rather than ‘flow’ from one group to the other. The present study sets out to characterize the temporal component of this apparently digital response.…”

Plasticity and superplasticity in the acclimation potential of the Antarctic mite Halozetes belgicae (Michael)

“…Fig.·3B shows the changes in cold hardiness of field-fresh H. belgicae from mid to late summer. There were highly significant differences between the SCP distributions of mites sampled on the 5 and 12 (Hawes et al, 2006b). ] Over a 5-day period, when environmental temperatures ranged between 0 and 5°C, fieldfresh mites showed a significant difference between SCPs (H=28.52; d.f.=10; P=0.001 (adjusted for ties); Kruskall-Wallis test), but no direct relationship with temperature (Fig.·3C).…”