Environmental physiology of three species of Collembola at Cape Hallett, North Victoria Land, Antarctica

Abstract

The environmental physiology of three speciesof Collembola: Cryptopygus cisantarcticus, Isotoma klovstadi (Isotomidae) and Friesea grisea (Neanuridae) was investigated from November 2002 to February 2003 at Cape Hallett, North Victoria Land, Antarctica. All three species were freeze avoiding, and while supercooling points were variable on seasonal and daily scales in I. klovstadi and C. cisantarcticus, they remained largely static in F. grisea. LT50 (temperature where 50% of animals are killed by cold) was -13.6, -19.1 and -19.8 degrees C for C. cisantarcticus, I. klovstadi and F. grisea, respectively. Upper lethal temperature was 34, 34 and 38 degrees C for C. cisantarcticus, I. klovstadi and F. grisea. Critical thermal minimum onset (the temperature where individuals entered chill coma) was ca. -7, -12 and -8 degrees C for C. cisantarcticus, I. klovstadi and F. grisea, and 25% of I. klovstadi individuals froze without entering chill coma. Critical thermal maximum (the onset of spasms at high temperature) was 30, 33 and 34 degrees C for C. cisantarcticus, I. klovstadi and F. grisea. Haemolymph osmolality was approximately 720 mOsm for C. cisantarcticus and 680 mOsm for I. klovstadi, and both species showed a moderate degree of thermal hysteresis, which persisted through the season. Desiccation resistance was measured as survival above silica gel, and the species survived in the rank order of C. cisantarcticus<< I. klovstadi = F. grisea. Desiccation resulted in an increase in haemolymph osmolality in I. klovstadi, and water was quickly regained by desiccation-stressed individuals that had access to liquid water, but not by individuals placed in high humidity, indicating that this species is unable to absorb atmospheric water vapour. SDS-PAGE did not suggest any strong patterns in protein synthesis either seasonally or in response to temperature or desiccation stress. Microclimate temperatures were measured at sites representative of collection sites for the three species. Microclimate temperatures were highly variable on a diurnal and weekly scale (the latter relating to weather patterns), but showed little overall variation across the summer season. Potentially lethal high and low temperatures were recorded at several sites, and it is suggested that these temperature extremes account for the observed restriction of the less-tolerant C. cisantarcticus at Cape Hallett. Together, these data significantly increase the current knowledge of the environmental physiology of Antarctic Collembola.

An invitation to measure insect cold tolerance: Methods, approaches, and workflow

“…Usually one thermocouple is used per insect, although it is also possible to increase throughput by carefully placing more than one (small) insect on a thermocouple (e.g. springtails; Sinclair et al, 2006a), or by connecting multiple thermocouples in series (Nedvěd et al, 1995). Thermocouples differ in the types of metal used, and in the diameter of the wire; any thermocouple type is acceptable if it returns valid measurements over an appropriate range of sub-zero temperatures and is compatible with the recording device.…”

“…Although cold-hardy populations of insects often have unimodal SCP distributions, some species (and also microarthropods like springtails and mites) have bimodal SCP distributions (Cannon and Block, 1988;Sinclair et al, 2006a;Figure 4). Bimodal SCP distributions can arise due to variation in the presence of ice nucleators or differences in body composition.…”

“…Aldrich, 1987), many authors simply decide on an a priori high group-low group divider by collating all SCPs and visually assessing a histogram for an obvious break and then compare the frequency, means or medians of the high and low groups among treatments using standard methods (e.g. Sinclair et al, 2006a). Because supercooling point distributions are seldom normal, and abnormally high or low values from one or two individuals can skew the entire distribution, care must be taken in using parametric statistics when comparing SCPs among samples or treatments.…”

“…For example, freezing occurs before chill coma in the freeze-avoidant Antarctic springtail, Isotoma klovstadi (Sinclair et al, 2006a) and in some freeze-tolerant cockroaches (Sinclair and Chown, 2005).…”

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

“…Although these organisms rarely, if ever, experience temperatures nearing 30 or even 258C, their heat tolerance is not surprising. A number of other studies, including those by Deere et al (2006), , Sinclair et al (2006) and Slabber et al (2007) have similarly shown appreciable heat tolerance in polar invertebrates. Such findings are consistent with the ''thermal sensitivity hypothesis,'' which states that the thermal sensitivity of invertebrates to a temperature rise declines with increasing latitude (Addo-Bediako et al 2000;Deutsch et al 2008).…”