Secretion Waterproofs

Biological Strategy

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Protect From Loss of Liquids

Water is essential to life. Liquids, mostly water, make up 70 to 90% of all living systems, and the loss of even a small percentage can mean the difference between life and death. Living systems must maintain a proper liquid balance, which is especially difficult in dry conditions. To do so, they must control the movement of liquids across their boundaries. Living systems do this using structures or waterproof materials to prevent or slow liquid movement. For example, when humans receive a cut, they must limit blood loss. Scattered throughout the bloodstream are lens-shaped structures that serve to plug the wound.

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Arachnids

Class Arachnida (“spider”): Spiders, mites, ticks, scorpions

Arachnids get a bad reputation, but they play an important role in the ecosystem by controlling insect populations. Almost half of the species in the class are spiders, and most live in terrestrial environments. Unlike insects, most arachnids have two body sections: the cephalothorax, which is the head and thorax fused together, and the abdomen. Mites and ticks, on the other hand, have only one body section that is relatively flat. This body shape comes in handy for the species that are parasitic, because it makes it harder for their hosts to bite or scratch them off.

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Glandular openings for the red velvet mite provide waterproofing by a secretion that fills pores and congeals.

“Features of Balaustium sp. include resistance to intense heat and desiccation, affinity for hot surfaces in bright light, abundance in semi-arid/arid biotopes, and a large pair of secretory glands called urnulae with no known function (defense secretion excepted). Here we show that the urnulae secrete a waterproofing barrier that reduces the mite’s cuticular permeability to water. Exposure to white light was used to stimulate release of the secretion; the urnulae protruded and exuded streams of red fluid at the tip of this structure that covered the entire body. Results showed that mites coated with urnulae secretion lost water at approximately half the rate of mites that did not secrete. Similarly, urnulae secretion coated mites demonstrated an increase in water-tightness of the cuticle reflected by a 9 ^OC elevation in temperature threshold for water loss on an evaporation curve, increasing their optimal temperature tolerance for survival (lethal permeability temperature, LPT). Results also show a 10 kJ/mol drop in activation energy (E_a) for water loss, representative of a substantial cuticular modification, and a decrease in Arrhenius frequency steric factor A, indicating an overall decrease in body water losses. The absence of a critical transition temperature (CTT), however, reveals that urnulae secretion coating functions to resist a phase change as the temperature rises, permitting the mites to cope with high temperature without succumbing to water and heat stress, by inhibiting cuticular breakdown.” (Yoder et al. 2008:419)

Jay A. Yoder, Chad M. Rigsby & Justin L. Tank (2008): Function of the Urnulae in Protecting the
Red Velvet Mite, Balaustium Sp., Against Water Loss and in Enhancing its Activity at High Temperatures, International
Journal of Acarology, 34:4, 419-425

Last Updated August 18, 2016

References

Journal article

Function of the Urnulae in Protecting the Red Velvet Mite, Balaustium Sp., Against Water Loss and in Enhancing its Activity at High Temperatures

International Journal of Acarology | 02/09/2009 | Jay A. Yoder, Chad M. Rigsby, Justin L. Tank

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