Habitat temperature and the temporal scaling of cold hardening in the high Arctic collembolan,Hypogastrura tullbergi(Schäffer)

Abstract

1. Cold tolerance is a fundamental adaptation of insects to high latitudes. Flexibility in the cold hardening process, in turn, provides a useful indicator of the extent to which polar insects can respond to spatial and temporal variability in habitat temperature.2. A scaling approach was adopted to investigate flexibility in the cold tolerance of the high Arctic collembolan, Hypogastrura tullbergi , over different time-scales. The cold hardiness of animals was compared from diurnal warming and cooling phases in the field, and controlled acclimation and cooling treatments in the laboratory. Plasticity in acclimation responses was examined using three parameters: low temperature survival, cold shock survival, and supercooling points (SCPs).3. Over time-scales of 24 -48 h, both field animals from warm diurnal phases and laboratory cultures from a 'warm' acclimation regime (18 °C) consistently showed greater or equivalent cold hardiness to animals from cool diurnal phases and acclimation regimes (3 °C).4. No significant evidence was found of low temperature acclimation after either hours or days of low temperature exposure. The cold hardiness of H. tullbergi remained 'seasonal' in character and mortality throughout was indicative of the summer state of acclimatization.5. These data suggest that H. tullbergi employs an 'all or nothing' cryoprotective strategy, cold hardening at seasonal but not diel-temporal scales.6. It is hypothesised that rapid cold hardening offers little advantage to these high Arctic arthropods because sub-zero habitat temperatures during the summer on West Spitsbergen are rare and behavioural migration into soil profiles offers sufficient buffering against low summer temperatures.

Plasticity in arthropod cryotypes

“…It shows little flexibility in summer cold-tolerance levels (Hawes et al, 2006), and overwintering mortality is greatly increased by manipulations of winter stress (Coulson et al, 2000). Thus, although on the one hand it does show seasonal phenotypic plasticity, its inflexibility outside typical environmental parameters suggests that this seasonal strategy is itself 'fixed' at a general level of tolerance appropriate to predictable summer and winter temperatures, rather than acclimating or acclimatizing to novel stress regimes (Coulson et al, 2000;Hawes et al, 2006).…”

“…Generalization 'General purpose' phenotype is produced Hypogastrura tullbergi (Hawes et al, 2006) (see text)…”

Contrasting strategies of resistance vs. tolerance to desiccation in two polar dipterans

“…Larvae were subsequently cooled from 4 to (308C at 0.5 min (1 . SCPs, defined as the temperature at the onset of the freezing exotherm, were identified using an eight channel datalogger interfaced to a computer and recorded using Picolog Recorder software (Pico Technology Limited, St. Neots, UK; see Hawes et al 2006).…”

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

“…Klok and Chown, 2005;Worland and Convey, 2001;Lee et al, 2006b;Hawes et al, 2006a). Is this evidence for species-specific or contextspecific variability?…”

“…Hawes et al, 2006a). However, the answer to the species-versus-context question can only be arrived at accretively by accumulating data on a range of species in a variety of environmental contexts.…”