The research will appear in the October issue of the Journal of Experimental Zoology Part A: Ecological Genetics and Physiology.
Monitoring Air Quality
For the study, scientists examined eight female water spiders, because females spend considerably more time in the air bells than males.
The team replaced the gas volume in each spider's air bell with pure oxygen, pure carbon dioxide, or a control of ambient air to test whether the spiders keep tabs on the air quality in the bells.
The team speculated that if the arachnids rely on air bells as a source of oxygen, their ability to detect elevated amounts of carbon dioxide and restore a proper balance is critical.
The test spiders only reacted to the carbon dioxide treatment, surfacing more frequently and increasing bell-building behavior until oxygen levels had been sufficiently replenished, co-author Taborksy said. (Related: "'New' Spider Species Weaves Uncommonly Regular Webs" [June 24, 2004].)
"The fact that the spiders did not react differently to the oxygen and control situations may indicate that they measure carbon dioxide levels in their bells rather than oxygen," he said.
"An increased carbon dioxide concentration may mean to the spider that the silk structure is not holding the air reserve well."
This meant the water spiders not only actively monitor the quality of the bell's atmosphere, but that they also depend on the bubbles for underwater respiration.
The new discovery provides scientists with an incentive to continue studying water spiders, Taborsky said.
Further research of the oxygen and carbon dioxide exchange through the silk membrane could provide a better understanding of the spiders' biology.
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