Cross-resistance (or cross-tolerance), where exposure to one kind of stress enhances resistance to others, is well known in insect physiological ecology (Hoffmann and Parsons 1991; Hoffmann et al. 2003b). In Section 5.4, the responses of upper or lower thermal tolerances to stress at the other end of the temperature spectrum were discussed in detail. While these effects are generally small and are probably the result of shared mechanisms, cross-resistance goes well beyond high and low-temperature interactions. It has been demonstrated in a wide range of laboratory selection experiments involving thermal tolerances, desiccation resistance, metabolic rate, and tolerance to ethanol in Drosophila. Stress protein expression is certainly characteristic of the response to many of these stressors (Feder and Hofmann 1999), and may well underlie the cross-tolerance here too. However, a reduction in metabolic rate is also thought to be a general response to stressful conditions, though this remains the subject of some dispute (Hoffmann and Parsons 1991; Chown and Gaston 1999).
That the response to one set of environmental stresses might have formed the basis for the response to another has been most widely explored in insect cold tolerance. It appears that the mechanisms that confer desiccation resistance have
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