Responses of Arthropods to Environmental Extremes
25
Some arthropods can escape extreme moisture andlor temperature conditions of semi-arid surface soil by burrowing or sheltering under stones
during daytime or even for longer periods (Hornung and Warburg 1996). For
instance, some spiders from southwestern Western Australia can dig burrows
the depth of which depends upon the the spiders aridity of the habitat
(Cloudsley-Thompson 1982). The entrances to the holes are usually sealed
and create favourable microhabitat conditions within their burrows, living
there for several months.
2.5.2
Cryptobiosis
Apart from behavioural adaptations, arthropods display analogous physiological responses to both low temperature and drought that may result in cryptobiosis (Barra et al. 1989). The term "cryptobiosis" is used to describe the
reduction of metabolism to a negligible amount. Arthropods enter the cryptobiotic state to survive the extreme conditions that usually occur in unstable
environments (Cloudsley-Thompson 1975). Although animals in cryptobiosis can survive extreme conditions for long periods, their viability generally
decreases with time (Cloudsley-Thompson 1988).
In general, processes enhancing the resistance of terrestrial arthropods to
both cold and desiccation are considered to be complementary (Scjlmme
1995, 1996), and in most cases desiccation resistant species may be preadapted to cold tolerance (Block 1996). For example, the responses of soil collembolans to drought and cold are the same (Fig. 2.6; Poinsot-Balaguer 1990).
A phase of active feeding is followed by a fasting period (probably controlled
intrinsically) during which morphological and metabolic changes occur. In
general, a latent and inactive life allows animals to overcome the environmental severity of Mediterranean habitats, and, apart from structural and
physiological adaptations, motionless instars can also survive extremes
including desiccated substrates and temperatures as low as -8°C (Asikidis
1989; Belgnaoui and Barra 1989; Argyropoulou 1993). In fact, by reducing the
amount of freezable water, partial dehydration enhances cold hardiness of
arthropods. Moreover, desiccation resulting in the accumulation of antifreezable compounds such as polyols lowers the supercooling point of arthropods
(Block 1996; Scjlmme 1996). Two specific cryptobiotic states, namely anhydrobiosis and ecomorphosis have been described in Mediterranean collembolans.
2.5.2.1
Anhydrobiosis
In general, the term "anhydrobiosis" is used to describe phenomena of latent
life caused by desiccation (Scjlmme 1996). As long ago as 1968, Poinsot ana-
25
Some arthropods can escape extreme moisture andlor temperature conditions of semi-arid surface soil by burrowing or sheltering under stones
during daytime or even for longer periods (Hornung and Warburg 1996). For
instance, some spiders from southwestern Western Australia can dig burrows
the depth of which depends upon the the spiders aridity of the habitat
(Cloudsley-Thompson 1982). The entrances to the holes are usually sealed
and create favourable microhabitat conditions within their burrows, living
there for several months.
2.5.2
Cryptobiosis
Apart from behavioural adaptations, arthropods display analogous physiological responses to both low temperature and drought that may result in cryptobiosis (Barra et al. 1989). The term "cryptobiosis" is used to describe the
reduction of metabolism to a negligible amount. Arthropods enter the cryptobiotic state to survive the extreme conditions that usually occur in unstable
environments (Cloudsley-Thompson 1975). Although animals in cryptobiosis can survive extreme conditions for long periods, their viability generally
decreases with time (Cloudsley-Thompson 1988).
In general, processes enhancing the resistance of terrestrial arthropods to
both cold and desiccation are considered to be complementary (Scjlmme
1995, 1996), and in most cases desiccation resistant species may be preadapted to cold tolerance (Block 1996). For example, the responses of soil collembolans to drought and cold are the same (Fig. 2.6; Poinsot-Balaguer 1990).
A phase of active feeding is followed by a fasting period (probably controlled
intrinsically) during which morphological and metabolic changes occur. In
general, a latent and inactive life allows animals to overcome the environmental severity of Mediterranean habitats, and, apart from structural and
physiological adaptations, motionless instars can also survive extremes
including desiccated substrates and temperatures as low as -8°C (Asikidis
1989; Belgnaoui and Barra 1989; Argyropoulou 1993). In fact, by reducing the
amount of freezable water, partial dehydration enhances cold hardiness of
arthropods. Moreover, desiccation resulting in the accumulation of antifreezable compounds such as polyols lowers the supercooling point of arthropods
(Block 1996; Scjlmme 1996). Two specific cryptobiotic states, namely anhydrobiosis and ecomorphosis have been described in Mediterranean collembolans.
2.5.2.1
Anhydrobiosis
In general, the term "anhydrobiosis" is used to describe phenomena of latent
life caused by desiccation (Scjlmme 1996). As long ago as 1968, Poinsot ana-