Adaptations for the maintenance of water balance by three species of Antarctic mites |
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Authors: | J B Benoit J A Yoder G Lopez-Martinez M A Elnitsky R E Lee Jr D L Denlinger |
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Institution: | (1) Department of Entomology, The Ohio State University, 318 W. 12th Ave, Columbus, OH 43210, USA;(2) Department of Biology, Wittenberg University, Springfield, OH 45501, USA;(3) Department of Zoology, Miami University, Oxford, OH 45056, USA |
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Abstract: | Three species of Antarctic mites, Alaskozetes antarcticus, Hydrogamasellus antarcticus and Rhagidia gerlachei, are abundant in the vicinity of Palmer Station, Antarctica. No single mechanism for reducing water stress was shared by
all three species. A. antarcticus and R. gerlachei (both ca. 200 μg) are over twice as large as H. antarcticus (ca. 90 μg), but all had similar body water content (67%) and tolerated a loss of up to 35% of their body water before succumbing
to dehydration. All imbibed free water and had the capacity to reduce water loss behaviorally by forming clusters. Alaskozetes antarcticus was distinct in that it relied heavily on water conservation (xerophilic classification) that was largely achieved by its
thick cuticular armor, a feature shared by all members of this suborder (Oribatida), and abundant cuticular hydrocarbons.
In comparison to the other two species, A. antarcticus was coated with 2–3× the amount of cuticular hydrocarbons, had a 20-fold reduction in net transpiration rate, and had a critical
transition temperature (CTT) that indicates a pronounced suppression in activation energy (E
a) at temperatures below 25°C. In contrast, H. antarcticus and R. gerlachei lack a CTT, have lower amounts of cuticular hydrocarbons and have low E
as and high net transpiration rates, classifying them as hydrophilic. Only H. antarcticus was capable of utilizing water vapor to replenish its water stores, but it could do so only at relative humidities close
to saturation (95–98 %RH). Thus, H. antarcticus and R. gerlachei require wet habitats and low temperature to counter water loss, and replace lost water behaviorally through predation. Compared
to mites from the temperate zone, all three Antarctic species had a lower water content, a feature that commonly enhances
cold tolerance. |
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Keywords: | Mite Water balance Cuticular hydrocarbons Critical transition temperature Antarctica |
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