Critical thermal limits and their responses to acclimation in two sub-Antarctic spiders: Myro kerguelenensis and Prinerigone vagans
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Despite the relative richness of spider species across the Southern Ocean islands remarkably little information is available on their biology. Here, the critical thermal limits of an indigenous (Myro kerguelenensis, Desidae) and an introduced (Prinerigone vagans, Linyphiidae) spider species from Marion Island were studied after 7–8 days acclimation to 0, 5, 10 and 15°C. Critical thermal minima (CTMin) were low in these species by comparison with other spiders and insects measured to date, and ranged from -6 to -7°C in M. kerguelenensis and from -7 to -8°C in P. vagans. In contrast, critical thermal maxima (CTMax) were similar to other insects on Marion Island (M. kerguelenensis: 35.0–35.6°C; P. vagans: 35.1–36.0°C), although signiWcantly lower than those reported for other spider species in the literature. The magnitude of acclimation responses in CTMax was lower than those in CTMin for both species and this suggests decoupled responses to acclimation. Whilst not conclusive, the results raise several important considerations: that oxygen limitation of thermal tolerance needs to be more widely investigated in terrestrial species, that indigenous and alien species might diVer in the nature and extent of their plasticity, and that upper and lower thermal tolerance limits might be decoupled in spiders as is the case in insects.