Recent reports indicate that the common brown dog tick, or kennel tick, Rhipicephalus sanguineus (Latreille) (Acari: Ixodidae) is a competent vector of Rocky Mountain spotted fever in the U.S.A. This tick is of concern to public health because of its high frequency of contact, as it has a unique ability to thrive within human homes. To assess the moisture requirements necessary for survival, water balance characteristics were determined for each developmental stage, from egg to adult. This is the first time that water relations in ticks have been assessed throughout the complete lifecycle. Notably, R. sanguineus is differentially adapted for life in a dry environment, as characterized by a suppressed water loss rate distinctive for each stage that distinguishes it from other ticks. Analysis of its dehydration tolerance limit and percentage body water content provides no evidence to suggest that the various stages of this tick can function more effectively containing less water, indicating that this species is modified for water conservation, not desiccation hardiness. All stages, eggs excepted, absorb water vapour from the air and can drink free water to replenish water stores. Developmentally, a shift in water balance strategies occurs in the transition from the larva, where the emphasis is on water gain (water vapour absorption from drier air), to the adult, where the emphasis is on water retention (low water loss rate). These results on the xerophilic-nature of R. sanguineus identify overhydration as the primary water stress, indicating that this tick is less dependent upon a moisture-rich habitat for survival, which matches its preference for a dry environment. We suggest that the controlled, host-confined conditions of homes and kennels have played a key role in promoting the ubiquitous distribution of R. sanguineus by creating isolated arid environments that enable this tick to establish within regions that are unfavourable for maintaining water balance.

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A B S T R A C TSand fiddler crabs, Uca pugilator, from North Carolina (NC) are two-times smaller than ones from Florida (FL). A water balance study was conducted to examine this size difference in relation to possible changes in habitat suitability. Like most crabs, U. pugilator are classified as hydrophilic, which is consistent with their preference for humid environments. In contrast to the North Carolina population, U. pugilator-FL loses water less rapidly and has higher percentage body water content, a water balance strategy that emphasizes retention. Conversely, the amount of body water required is less for U. pugilator-NC, enabling it to maintain water balance despite having a higher water loss rate. Both tolerated only about 1/4 loss of body water before succumbing to desiccation. Neither experienced a critical transition temperature, CTT. We concluded that water balance profiles of these two populations are complementary, representing trade-offs that permit survival in a moisture-rich habitat. Lower body water content, however, overlaps with features of arthropods that thrive at low temperature, suggesting that U. pugilator-NC may be more cold tolerant.