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• Title: Cold-Hardiness in the Wolf Spider Pardosa Groenlandica (Thorell) with Respect to Thermal Limits and Dehydration (Short Communication) (Report)
• Author : Journal of Arachnology
• Release Date : January 01, 2008
• Genre: Life Sciences,Books,Science & Nature,
• Pages : * pages
• Size : 195 KB

Description

Arthropods that live in sub-zero temperatures for at least part of the year survive by one of two physiological and biochemical responses. At least for insects (Bale 2002), one way is tolerance of ice crystal formation in their bodies (freeze tolerance), and the other is avoidance of ice crystal formation (freeze avoidance). Ice crystal formation is avoided by super-cooling, which depresses the freezing point (Sinclair 1997; Renault et al. 2002). The super-cooling temperature depression is often used to determine cold-hardiness in invertebrates, and the temperature at which ice crystals form is called the super-cooling point SCP (Renault et al. 2002). Several physiological processes are known to cause super-cooling and SCP depression. These include accumulation of poly-ol compounds in the hemolymph (thus increasing the osmotic pressure), dehydration (also increasing osmotic pressure), synthesis of thermal-hysteresis protein, or evacuation or masking of ice-nucleation factors in the gut (Duman 1979; Somme 1982; Zachariassen 1982; Aunaas et al. 1983; Cannon & Block 1988; Danks 2005). Cold hardiness is particularly important in spiders as they are not known to be freeze-tolerant (Kirchner 1987). Among spiders there are a variety of strategies for surviving sub-zero temperatures (Schaefer 1977; Kirchner 1973, 1987). There are two main strategies to survive freezing temperatures by super-cooling temperature depression according to Kirchner (1987). One physiological strategy is to maintain a relatively constant SCP throughout the year. This strategy is found in species that have low (SCP = -3[degrees] - -7[degrees]C) or medium (SCP = -7[degrees] - -15[degrees]C) cold hardiness, by Kirchner's categories (Kirchner 1987). According to this idea, only species with high cold hardiness (SCP -17[degrees]C) decrease their SCP as seasons proceed. The second physiological strategy is a lowering of the SCP as the temperature decreases through seasons. This strategy is found in species that have high cold hardiness. In this study we used a common wolf spider (Lycosidae) Pardosa groenlandica (Thorell 1872) to test four research goals regarding the nature of cold hardiness in spiders. The species is found across northern Canada, Alaska, and Siberia, in terrain that ranges from exposed mountain slopes, to open plains, to stony coastlines (Dondale 1999). All the habitats share one feature: all experience several months at sub-zero temperatures, so that the species must be adapted for cold hardiness to remain active below 0[degrees]C. However, it is known that species of Pardosa from different regions, with differences in mean monthly temperatures, vary in their SCP. For example, Pardosa species from Newcastle-upon-Tyne (UK) had higher SCP than a variety of Lycosidae from cooler climates (Kirchner 1987; Bayram & Luff 1993). Therefore, our first goal was to test whether P. groenlandica has a lower SCP than reported for the Pardosa species from warmer climates. We also determined the thermal limit of locomotion, at which temperature individuals are still active. The habitat of P. groenlandica would classify it as a species of medium cold hardiness (Kirchner 1987). Our second goal was to test whether P. groenlandica maintains the same SCP through seasons, as would be predicted by Kirchner (1987). Controlled dehydration is known to be one physiological response to decreasing the SCP in insects (Danks 2005) and in wolf spiders (DeVito & Formanowicz 2003). Since an increase in poly-ol concentration was proposed to be physiologically demanding in winter-active species (Duman 1979), dehydration would be a plausible alternative to increasing the osmotic pressure. Therefore, our third goal was to test whether dehydration contributes to cold hardiness and SCP depression in P. groenlandica. Finally, a difference in the SCP between sexes is known in some arthropods but is rare in spiders (Kirchner 1987; Salin et al. 2000). Our fourth goal was to tes

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