The Dynamics of Water Relations
, 8E
CJ)
o
E
19
III
IV V VI VII VII IX X XI
Fig. 2.1. Seasonal changes in haemolymph osmolality of the isopod Armadillo officinalis. I-XI
months. (Warburg 1987a)
water conditions. Fasting is generally associated with a reduction in high
energy-consuming activities, such as locomotion and reproduction, and coupled with diminishing transpiration.
Tolerance strategies involve water absorption directly from moist particles
through the ventral tube of Collembola or the uropods of isopods, specific
anatomical structures such as the subelytral cavity in some desert beetles
(Cloudsley-Thompson 1965; Zachariassen et al. 1987), egg deposition in
favourable micro sites, behavioural adaptations, and construction of specific
structures such as cocoons for egg deposition and larval development (Cloudsley-Thompson 1982,1983). Two specific tolerance mechanisms, namely anhydrobiosis and ecomorphosis, involving both structural and metabolic
adjustments have been described in only a few collembolans
2.3
The Dynamics otWater Relations
Depending on the concentrations of Na+ and Cl-, the osmolality of the haemolymph of arthropods determines their water balance to a great extent. In
general, higher values of blood osmotic pressure are measured in summer
(Figs 2.1, 2.2), and blood osmolality is also found to be food dependent.
Increases in osmotically active compounds, as well as decreases in the
amount of haemolymph, result in increased blood osmolality.
Some species such as the collembolan Orchesella cincta can regulate osmotic pressure under the progressive dehydration of their substrates, and fasting
animals exhibit constant blood osmolality and almost constant body water
content in all states (Verhoef and Li 1983). Initially, a rise in feeding activity of
the animals is recorded, whereas foraging activity and moulting cease during
the advanced stages of dehydration and the animals enter a pre-ecdysial state.
Locomotory and metabolic activities as well as transpiration become minimal.
, 8E
CJ)
o
E
19
III
IV V VI VII VII IX X XI
Fig. 2.1. Seasonal changes in haemolymph osmolality of the isopod Armadillo officinalis. I-XI
months. (Warburg 1987a)
water conditions. Fasting is generally associated with a reduction in high
energy-consuming activities, such as locomotion and reproduction, and coupled with diminishing transpiration.
Tolerance strategies involve water absorption directly from moist particles
through the ventral tube of Collembola or the uropods of isopods, specific
anatomical structures such as the subelytral cavity in some desert beetles
(Cloudsley-Thompson 1965; Zachariassen et al. 1987), egg deposition in
favourable micro sites, behavioural adaptations, and construction of specific
structures such as cocoons for egg deposition and larval development (Cloudsley-Thompson 1982,1983). Two specific tolerance mechanisms, namely anhydrobiosis and ecomorphosis, involving both structural and metabolic
adjustments have been described in only a few collembolans
2.3
The Dynamics otWater Relations
Depending on the concentrations of Na+ and Cl-, the osmolality of the haemolymph of arthropods determines their water balance to a great extent. In
general, higher values of blood osmotic pressure are measured in summer
(Figs 2.1, 2.2), and blood osmolality is also found to be food dependent.
Increases in osmotically active compounds, as well as decreases in the
amount of haemolymph, result in increased blood osmolality.
Some species such as the collembolan Orchesella cincta can regulate osmotic pressure under the progressive dehydration of their substrates, and fasting
animals exhibit constant blood osmolality and almost constant body water
content in all states (Verhoef and Li 1983). Initially, a rise in feeding activity of
the animals is recorded, whereas foraging activity and moulting cease during
the advanced stages of dehydration and the animals enter a pre-ecdysial state.
Locomotory and metabolic activities as well as transpiration become minimal.