Dark Banquet
Page 27
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†143 Dr. Spotte is a marine scientist and a prolific author He has published on topics ranging from modern zoos to mermaids. “I’m just an ologist,” he told me.
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*144This would be comparable to aliens capturing a jockey and a basketball player, then calling them different species because of the observed size differences. Presumably, if they had a greater sample size (a whole town, perhaps), they’d realize that they were looking at a single species.
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*145In some ways this gas exchange mechanism is similar to the one that exists between the respiratory airways of terrestrial vertebrates and the tiny alveoli located in their lungs. Oxygen (which is at a higher concentration in the water surrounding the gills than it is inside the feathery gill filaments) diffuses from the water into these ultra-thin-walled structures. The oxygen then passes into blood being carried by tiny vessels within the filaments (in much the same way as oxygen passes from alveoli into the capillaries that surround them). These blood vessels then carry the oxygenated blood away from the gills to be distributed to the tissues of the fish’s body. One major difference between the circulatory systems of fish and other vertebrates like amphibians, reptiles, birds, and mammals is that in fish, the oxygenated blood does not return to the heart before being pumped to the body. The fish heart is a rather simple, two-chambered pump (one atrium and one ventricle), rather than a three-chambered (amphibians and most reptiles) or four-chambered structure (crocodilians, birds, and mammals).
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†146 A recent claim by researchers Jansen Zuanon and Ivan Sazima that candirus feed passively (i.e., the blood pressure of the prey literally pumps the blood into the candiru’s digestive system) remains untested and Stephen Spotte is extremely skeptical. “From watching candirus feed, it appears that a rapid pumping mechanism of some sort is being used. Were ingestion passive, no such pumping activity, in fact, no movement would be necessary. The process would be like filling a bottle of water from a faucet.”
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*147The identity of the patient (Silvio Barbossa) was revealed in a more recent Animal Planet segment on parasites.
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*148In separate trials, they added solutions of urine, blood, and ammonia to tanks containing captive candiru, and in each case they saw no visible change in the candiru’s behavior. In fact, only when they released a fish into the water did the candiru perk up.
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*149Interestingly, humans with hookworm infections are half as likely to have asthma or hay fever. The idea is that some parasites survive by down-regulating their host’s immune system. With its primary defense mechanism throttled back, it’s far less likely that the body will mount an inflammatory response against a harmless allergen or attack its own tissues. On a related note, it appears that in addition to selecting for more antibiotic resistant bacteria, our 99 percent germ-free culture has resulted in hypersensitive immune systems. The end result is an increase in the incidence of asthma, allergies, and some autoimmune diseases.
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*150Likewise, mosquitoes also feed on substances other than blood, namely nectar and fruit juice. In Anopheles, the genus that transmits malaria, only the female mosquito is obliged to seek out a blood meal. Unfortunately, the lack of card-carrying vampire status is completely irrelevant when one looks at the astronomical death toll associated with these insects. For example, it’s been estimated that mosquito-transmitted malaria kills one person every twelve seconds.
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*151The oldest evidence for a blood-feeding lifestyle comes from a fossil “protomosquito” from the Triassic period (approximately 220 million years ago). Since there were no flowering plants present, and therefore no nectar to sip, the elongated proboscis of this insect presumably functioned in much the same way as it does in extant mosquitoes.
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†152 It also comes in a second flavor (hemolymph), which is shed in a variety of arthropods groups.
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*153In a chemical cascade, the products of each step in the chemical reaction are integral to the step that follows.
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*154There is some debate as to just how many mosquitoes an aerial insectivore like a little brown bat (Myotis lucifugus) can eat in a single night. Estimates range from an insubstantial number to six hundred mosquitoes per hour (a number that always seemed a bit high to me).
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Copyright © 2008 by William A. Schutt Jr.
Illustrations copyright © 2008 by Patricia J. Wynne
All rights reserved.
Published in the United States by Harmony Books, an imprint of the Crown Publishing Group, a division of Random House, Inc., New York.
www.crownpublishing.com
Harmony Books is a registered trademark and the Harmony Books colophon is a trademark of Random House, Inc.
Library of Congress Cataloging-in-Publication Data
Schutt, Bill.
Dark banquet : blood and the curious lives of blood-feeding creatures / Bill Schutt; illustrated by Patricia J. Wynne.
p. cm.
Includes bibliographical references.
1. Blood-feeding creatures. I. Title.
QL756.55.S38 2008
591.5'3—dc22 2008003061
eISBN: 978-0-307-44992-4
v3.0