LIFE IN A SHELL

LIFE IN A SHELL

Donald C. Jackson
Copyright Date: 2011
Published by: Harvard University Press
https://www.jstor.org/stable/j.ctt2jbs04
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  • Book Info
    LIFE IN A SHELL
    Book Description:

    Trundling along in essentially the same form for some 220 million years, turtles have seen dinosaurs come and go, mammals emerge, and humankind expand its dominion. Is it any wonder the persistent reptile bested the hare? In this engaging book physiologist Donald Jackson shares a lifetime of observation of this curious creature, allowing us a look under the shell of an animal at once so familiar and so strange. Here we discover how the turtle’s proverbial slowness helps it survive a long, cold winter under ice. How the shell not only serves as a protective home but also influences such essential functions as buoyancy control, breathing, and surviving remarkably long periods without oxygen, and how many other physiological features help define this unique animal. Jackson offers insight into what exactly it’s like to live inside a shell—to carry the heavy carapace on land and in water, to breathe without an expandable ribcage, to have sex with all that body armor intervening. Along the way we also learn something about the process of scientific discovery—how the answer to one question leads to new questions, how a chance observation can change the direction of study, and above all how new research always builds on the previous work of others. A clear and informative exposition of physiological concepts using the turtle as a model organism, the book is as interesting for what it tells us about scientific investigation as it is for its deep and detailed understanding of how the enduring turtle “works.”

    eISBN: 978-0-674-05890-3
    Subjects: Zoology, Biological Sciences, Aquatic Sciences

Table of Contents

  1. Front Matter
    (pp. [i]-[vi])
  2. Table of Contents
    (pp. [vii]-[x])
  3. 1 THE TURTLE’S SHELL
    (pp. 1-18)

    A turtle lives inside a shell. This is a familiar fact that we all take for granted, but what does it mean to live this way? A shell is heavy and cumbersome. How does it affect a turtle’s ability to move about, on land or in water? Because the shell is so heavy, what keeps an aquatic turtle from sinking to the bottom? How does a turtle breathe without an expandable rib cage like the one we have? How do turtles manage to have sex with intervening armor? These and many other questions arise when you begin to think seriously...

  4. 2 BUOYANCY
    (pp. 19-32)

    I used to keep turtles in my lab in a large glass aquarium. They were redeared sliders (scientific name: Trachemys scripta elegans), a species commonly sold in pet stores and also a common species in turtle research. Often I watched the turtles swim lazily about or remain motionless in mid-water and then periodically paddle up to the surface to breathe. Usually my mind would remain blank, hypnotized by the effortless and graceful movements of these creatures that were clearly at home in their natural element. As I watched, though, I gradually grew curious about how they were able to hang...

  5. 3 THE BREATHING TURTLE
    (pp. 33-52)

    One would assume that breathing must be difficult and challenging for an animal encased in a rigid shell. And, indeed, it would be if the poor creature were completely enclosed. But a turtle has soft, flexible pockets of skin where its limbs emerge. These pockets move in and out as the turtle expires and inspires. As we will see, the turtle in its shell can not only breathe but can do so at quite a modest metabolic cost, despite its rigid enclosure. Because of its shell, the breathing mechanism of the turtle is unusual. Unlike other reptiles that employ trunk...

  6. 4 TORTUGUERO
    (pp. 53-69)

    I vividly remember walking along the beach, just above the tide line, straining my eyes in the dark for the faint discoloration in the sand that would reveal the recent passage of a sea turtle. Usually a companion with a more experienced or sensitive eye than mine would spot it first, and then we would very quietly follow the path up the beach. Sometimes it would prove to be the return path of a turtle that had already nested, or one leg of a half-moon pattern made by a turtle that for some reason aborted its nesting mission. But on...

  7. 5 OVERWINTERING WITHOUT BREATHING
    (pp. 70-88)

    The time is late fall in central Wisconsin. The sun has nearly gone down, the sky is clear, and the temperature is falling. A painted turtle that lives in a quiet pond swims to the surface, takes several breaths, raising the level of oxygen in its lungs, and then sinks back into the water. The water is already so cold that the turtle’s metabolism has slowed to a small fraction of what it is in the summer, and the turtle may not have to come up again to breathe for many hours. When it does try again to breathe, it...

  8. 6 LIVING WITHOUT OXYGEN
    (pp. 89-112)

    At regular intervals throughout the winter, we entered the cold room down the hall from my laboratory, drew blood samples from the submerged turtles, and evaluated the turtles’ condition. Week after week and month after month, my colleague, Gordon Ultsch, and I were amazed to find turtles that were still responsive. These turtles, western painted turtles (Chrysemys picta bellii), were in very cold water (3°C) that was continuously bubbled with pure nitrogen gas; in other words, the turtles were anoxic, meaning they had no oxygen. They were unable to breathe, just as would be the case if they were trapped...

  9. 7 THE HEART OF A TURTLE
    (pp. 113-134)

    I once did an experiment in which I periodically sampled arterial blood from a turtle submerged in water at room temperature. My purpose was to observe how rapidly the blood oxygen was depleted during a breath-hold period. Because the turtle had breathed shortly before submergence, the oxygen level was high at the beginning of submergence but became progressively lower in the first several samples I took. This was expected, because the turtle’s tissues were consuming oxygen and the blood oxygen was not being replenished by breathing. The next sample, however, surprised me. It showed an increase in blood oxygen. How...

  10. 8 LIFE IN THE SLOW LANE
    (pp. 135-149)

    The tortoise won the race against the hare not because of its swiftness but because of its persistence. The much faster hare raced ahead but then stopped to rest and fell asleep. The plodding tortoise passed it by and reached the finish line first. As Aesop moralized, “Slow but steady wins the race.”

    Slow moving and plodding suggest a low rate of metabolism and, sure enough, if you compare a tortoise with a hare, the metabolism of the hare is much higher, whether the two are at rest or racing against each other. The hare is a mammal, a warm-blooded...

  11. EPILOGUE
    (pp. 150-156)

    When I decided to stop doing research and close down my lab, I still had four painted turtles in my animal facility. They were healthy animals that had never been used in an experiment. I had to decide how to dispose of these four beautiful turtles. The obvious option, which is generally the rule for surplus experimental animals, was to euthanize them humanely by administering an anesthetic overdose. But this was not the way I wanted it all to end. I procrastinated and finally took the dilemma home and consulted with my wife Diana. I explained the situation to her....

  12. REFERENCES
    (pp. 159-170)
  13. ACKNOWLEDGMENTS
    (pp. 171-172)
  14. INDEX
    (pp. 173-179)