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Biology Today - Pure Joy

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									                                                 Biology Today

                                                    Pure Joy
                                                Maura C. Flannery
                                                     Department Editor


    Doing the research for this column      effectively land large prey. He found      age in an adult vertebrate, and the
was pure joy. I keep a folder labeled       that while B. gabonica is an extreme       marine iguanas seem capable of
‘‘Animals,’’ and I sat down with it one     case, a comparison of ground-dwelling      repeating growth and shrinkage cycles
day. I ended up spending a wonderful        with tree-dwelling snakes showed that      several times during their lives, pro-
afternoon reading about fascinating         the average passage time for ground        viding the animal with an unusual
adaptations. This column is admittedly      dwellers was 145 days longer than for      adaptation to starvation conditions.
a potpourri, but what all the items         tree dwellers, with some tree dwellers
here have in common is that they are        having passage times that seem posi-
all reminders of why many of us went        tively supersonic next to B. gabonica.     Hot Clams & Slow
into biology—it’s just the most inter-      The slender arboreal snake Uromacer        Tubeworms
esting subject going.                       oxyrhyncus eliminates waste in less
                                                                                           One of the problems with investi-
                                            than two days. Lillywhite attributes
                                                                                       gating animals is that it’s often difficult
                                            this difference to the fact that tree
Slow Digestion                                                                         to study them where they live. This
                                            dwellers need to be mobile and the
                                                                                       is particularly true of organisms that
    I want to start with snakes because     extra weight of waste would slow their
                                                                                       reside in the deep ocean, but biologists
this item is strange and wonderful.         movements. For ground dwellers, on
                                                                                       are finding ways to explore the habits
It includes the kind of statistics that     the other hand, extra weight in the
                                                                                       of even these creatures. Japanese
students love, but it also makes a seri-    form of waste material can be an
                                                                                       researchers used video cameras and
ous point about adaptation as well.         advantage especially since it accumu-
                                                                                       temperature sensors to study colonies
Elizabeth Pennisi (1999a) reports on        lates in the hindgut. Snakes with such
                                                                                       of the giant white clam, Calyptogena
the research of Harvey Lillywhite of        extra heft have been found to strike
                                                                                       soyoae, more than 1,100 meters below
the University of Florida who investi-      more quickly and to get a firmer grip
                                                                                       the surface of Sagami Bay in Japan
gated ‘‘chronic constipation’’ in some      on prey.
                                                                                       (Van Dover 1999). C. soyoae belongs
snake species. But ‘‘chronic’’ is an                                                   to the same genus as clams living
understatement. In a study of the rate      Shrinking Iguanas                          near hydrothermal vents in the eastern
of defecation in a number of large,                                                    Pacific, and like these clams, it is a
                                               But while some snakes do better
ground-dwelling snakes, Lillywhite                                                     host for endosymbiotic, sulfide-oxidiz-
                                            with extra weight, some iguanas do
found that the Gabon viper Bitis gabon-                                                ing microorganisms from which it
                                            better by not just slimming down, but
ica had the longest ‘‘passage time.’’                                                  draws nourishment. But C. soyoae lives
                                            by actually shrinking. Researchers
While it ate a number of times during a                                                in a much cooler environment, in sedi-
                                            found that some members of a popula-
year, it only defecated once in 420 days.                                              ments into which seep cold waters rich
                                            tion of Galapagos marine iguanas of
    While Metamucil or Ex-Lax might                                                    in sulfides.
                                            the species Amblyrhynchus cristatus
seem in order for this poor creature,                                                      Observations made with video cam-
                                            became shorter over a period of two
Lillywhite argues that long-term reten-                            ˜                   eras and temperature sensors over an
                                            years during El Nino events when
tion of waste is not a matter of real       food supplies were low (Wikelski &         18-month period included evidence for
constipation but of bulking up to more      Thom 2000). Large individuals shrank       11 cases of spawning by both sexes,
                                            proportionately more than small ones,      and in each case, the spawning was
                                            and females shrank more than males of      associated with a brief rise in water
 Maura C. Flannery is Professor of Biol-
 ogy and Associate Director of the          the same size. The lizards that shrank     temperature of only 0.1–0.2° C. The
 Center for Teaching and Learning at        more lived longer both because they        rise lasted less than two hours and was
 St. John’s University, Jamaica, NY         could move around more easily to           not associated with lunar or seasonal
 11439; e-mail: flannem@stjohns.edu.                                                   cycles. To test the hypothesis that the
                                            forage and because they expended less
 She earned a B.S. in biology from Mary-
 mount Manhattan College; an M.S.,          energy to do so. The extent of shrink-     water temperature change triggered
 also in biology, from Boston College;      age, up to 20% of body length, indi-       spawning, researchers placed a plastic
 and a Ph.D. in science education           cates that this couldn’t just be the       dome with a light bulb attached over
 from New York University. Her major        result of a decrease in cartilage and      a group of clams in situ. When lit, the
 interests are in communicating sci-                                                   light bulb increased the temperature
                                            connective tissue, but that bone
 ence to the nonscientist and in the
 relationship between biology and art.      absorption also had to be involved.        at the surface by 2.2° C, and spawning
                                            This is the first report of such shrink-   by several clams began within five

132 THE AMERICAN BIOLOGY TEACHER, VOLUME 63, NO. 2, FEBRUARY 2001
minutes of turning on the light. The         tion demands for the two environments      noise (Pennisi 1999b). In about half of
males spawned first, as is often the         are so different. Walking on land is       the approximately 40 manakin species,
case with clams living in shallow            much the same for crabs and insects        the males use their wings to make
waters, and it may be that the release       and mammals, with some alterations         clicking and rattling sounds to attract
of sperm triggers spawning by                due to the number of legs involved. But    mates. What makes this practice
females. There was no spawning in            walking in the much denser medium of       unusual is that it has required rather
the control group.                           water requires a different approach.       costly reshaping of the manakin’s
    This piece of research is interesting    The crab’s thin body and sideways          feather and wing structures. These are
for two reasons. First, it is amazing        walk help to reduce drag, and in under-    costly in the sense that they may
what can be learned about animals            water video movies it’s evident that       impair the bird’s ability to fly, which
that live in such inaccessible places.       the crab uses its legs more to push off    brings up the issue of the balance
Granted, this was an expensive experi-       than to maintain balance.                  between useful adaptations and char-
ment since the services of a submers-            The second item deals with the         acteristics shaped by sexual selection.
ible were needed, but it is an indication    snapping shrimp, Alpheus heterochaelis.        The reshaping involves a change in
that deep waters are coming more and         It has a large snapper claw that slams     structures such as the ulna which is
more within reach of biologists. Sec-        shut whenever the shrimp is disturbed.     a thin bone in birds related to the
ond, this work indicates that the envi-      This snap sprays the intruder with a       manakins such as flycatchers. In the
ronment at great depths in the ocean         jet of water that usually sends it off     clicking manakins, the ulna is thicker
is not as unchanging as previously           in another direction. Biologists had       and has knobs to help support the
thought. Water temperature does              assumed that the crackling noises          enlarged muscles attached to the feath-
change, perhaps as a result of water         heard near snapping shrimp colonies        ers. Among manakins, the species with
circulation patterns. It makes sense         were due to the claws banging shut.        the most unusual wings are the club-
that such changes would be used by           But now a team of Dutch physicists         winged manakins. When males of this
clams to improve reproductive effi-          and biologists reports that the crack      species display, they lean forward and
ciency. In shallow-water clam species,       is due to a collapsing bubble outside      flip their wings back and then forward.
fertilization rates increase with syn-       the shrimp’s claw.                         To do this, they have to rotate the
chronization of spawning. Also, the              The shrimp’s crackling sound has       elbow joint, a motion that is uncommon
large number of larvae generated in          been studied since World War II, when      in birds. While the muscles attached
these spawning events have a better          the Navy became interested because         to the elbow are small in most birds,
chance of surviving predation.               the noise from shrimp colonies could       they are bulky and strong in club-
    In another piece of research on a        drown out the sonar used to detect         winged manakins. Kim Bostwick of the
relative of a hydr ot he rm al ve nt         submarines. The assumption has             University of Kansas, Lawrence, who
dweller, biologists from Penn State          always been that the sound came from       did this study, speculates that all these
have investigated a tubeworm of the          the snapping, but here again, the video    changes must impede the flying ability
genus Lamellibrachia living in hydrocar-     camera became a useful research tool.      of these birds, though she has yet to
bon seeps on the Louisiana continental       In each of a number of videos of the       do the research to confirm this. She is
slope. They found that it requires           shrimp’s claw closing, an air bubble       planning to look at both manakins who
between 170 to 250 years to grow             can be seen moving out of the claw         have secondarily lost their ability to
to a length of two meters (Bergquist,        with the water jet. The bubble enlarges    make clicks and at those who make
Williams & Fisher 2000). This is very        and then breaks up into a mass of          clicks with their tail or vocal cords
different from the growth rate of its        tiny bubbles in a process called cavita-   rather than with their wings.
relatives in hydrothermal vents; these       tion, and with this comes the crackling
are among the fastest growing inverte-       noise. As Kathryn Brown (2000)
brates known. It is not just a variance      explains in an article on the research,    Birds & the Sense of Smell
in temperature that explains these rate      the shrimp ‘‘clamps its claw so rapidly
                                             that a water jet gushing from the claw         While some birds are making sounds
differences; the availability of nutrients                                              in unusual ways, others are making
                                             first loses and then gains pressure,
is also a factor. This is a good example                                                use of a sense that up until recently
                                             causing an air bubble in the jet to
of how closely related invertebrates                                                    wasn’t considered very important in
                                             swell and collapse with a pronounced
are able to adapt to very different                                                     birds: the sense of smell. The accepted
                                             ‘snap!’ The imploding bubble gener-
environmental conditions.                                                               view, based on early work on avian
                                             ates shock waves that stun nearby prey
                                             and ward off other shrimp’’ (p. 2020).     brain anatomy—including the size of
                                                                                        the olfactory bulb—is that birds have
Crustaceans on the Move                      This is a good example of the fact that
                                                                                        little or no ability to smell. But research
                                             it often pays to revisit old problems
   Before I leave the topic of water-        and old explanations. Often new            done over the past 30 years indicates
dwelling invertebrates, I want to men-       equipment provides new kinds of            that for many species this is hardly
tion two other items, both related to        information that make revision of old      the case (Malakoff 1999). Studies on
the movements of crustaceans. First is       answers necessary.                         brain anatomy begun in the late 1960s
the crab’s walk. Carl Zimmer (2000a)                                                    among 151 bird species showed that
nicely describes how crabs are ‘‘engi-                                                  the olfactory bulb made up as little
neered’’ to move efficiently both on
                                             Wing Restructuring                         as 3% of the brain in small songbirds
dry land and in the water. Such adapt-          Neotropical birds called manakins       such as the chickadee, but as much
ability is difficult because the locomo-     also have an unusual way to make           as 37% in seabirds like the petrel.

                                                                                                           BIOLOGY TODAY 133
Other research showed that turkey vul-       feet were more sought after as mates       a recent common ancestor. This ap-
tures can find food solely on the basis      than males with green bracelets. It        proach seems to have yielded results
of scent, and that pigeons, those gour-      has been hypothesized that attractive      that bring reasonable order to this
mets of city streets, can detect rather      ornamentation might signal the pres-       group of birds’ family tree. For exam-
subtle scents. Homing pigeons whose          ence of good genes and so by selecting     ple, Furnarius in the past had been
sense of smell has been blocked take         mates with such adornment, members         thought to be only distantly related
much longer to find their home base          of the opposite sex are increasing the     to other genera that nest in earthen
and in some cases never make it. Smell       chance that their offspring will have      burrows. But the fact that all these
may also help some birds, such as            a desirable genetic makeup. In this        birds have nests with linings that are
European starlings, locate the plants        case, however, genes just can’t be         cup-shaped and made of grass and
they use to build their nests and help       involved. As this study shows, off-        strips of bark, indicates that they are
chickens avoid bad-tasting insects.          spring may in fact be more robust for      probably closely related.
This is another good example of an           reasons that have absolutely nothing
area of research that has blossomed          to do with genes. Still, this investiga-
as biologists have moved beyond a            tion is very preliminary. The relation-
                                                                                        Smoke Detector
long-held assumption. Such assump-           ship between testosterone and health-          I am interested in the metaphors
tions are important in the sense that        ier chicks has yet to be established       biologists use to explain their work,
they prevent researchers from explor-        for zebra finches since the researchers    for example, to describe adaptations
ing areas that are indeed fruitless, but     destroyed the eggs in the process of       in organisms. So when I saw an article
at the same time, the work on birds’         measuring hormone levels. There is         with the title, ‘‘Insect Antenna as a
sense of smell is a reminder that            also the question of how females con-                                          ¨
                                                                                        Smoke Detector,’’ I read on (Schutz et
assumptions need to be revisited from        trol testosterone levels in the eggs. It   al. 1999). It seems that larvae of the
time to time since new techniques and        may be that mating with attractive         jewel beetle Melanophila acuminata can
viewpoints can call them into question.      males increases arousal; there is a        only develop in the wood of trees that
                                             study showing that — in canaries           have just died in a fire. This level of
                                             again—there is a relationship between      choosiness means that the beetle has
Sexy Bracelets                               hormone levels in the females’ blood       to be able to detect a fire from some
   Though equipment of some kind is          and in the eggs. In any case, the brace-   distance. M. acuminata does have
necessary for almost all biological          let study is a nice example of a ‘‘natu-   paired thoracic pit organs that are
work, sometimes the consequences of          ral’’ experiment which teases apart        extremely sensitive infrared receptors,
using a particular device are unex-          genetic and nongenetic factors that        but heat can only be detected when
pected. Research on zebra finches pro-       usually go hand-in-hand.                   the beetle is relatively close to the fire.
vides a case in point. The zebra finch                                                  Is there a way for it to find more
is much studied because it is a small                                                   distant conflagrations? Researchers in
bird that easily adapts to life in the
                                             Constructing a Family Tree                 Germany have looked for such a
lab. The set of experiments I want to            Teasing out the genetic relation-      capacity in the beetle’s antennae. They
discuss here is on a topic which is of       ships among members of another             removed antennae from live beetles and
great interest to biologists, that is, the   group of birds has proven particularly     immediately connected each antenna to
costs and benefits of sexual selection.      difficult for ornithologists. There are    a gas chromatograph designed to detect
Researchers found that females who           240 species of ovenbirds that inhabit      volatile substances in burning wood.
mated with more attractive males             parts of Central and South America,        The antennae were sensitive to several
deposited more testosterone in their         and until now, it has been impossible      of the chemicals released by smolder-
eggs (Vogel 1999). Studies on canaries       to construct a convincing ovenbird         ing Pinus sylvestris wood, particularly
suggest that chicks exposed to more          family tree. Now researchers at the        methoxylated phenols that are pro-
testosterone during development              University of Kansas have accom-           duced during the incomplete combus-
thrived because they begged more for         plished this task by focusing on the       tion of lignin. So it looks as if this
food and grew faster; the same may           types of nests these birds create to       jewel beetle does indeed have a smoke
be true for zebra finches. Here is a         incubate eggs away from harsh weather      detector—and a detector tuned to the
case where healthier chicks resulting        and predators (Holden 1999). The           residues of burning woods. This is of
from mating with a desirable male            ovenbirds are known for their nests        interest not only to beetle-lovers; a
may not be the result of the male’s          which come in a great variety of           biosensor based on this system might
having better genes, but of the female       shapes and sizes; in fact, they are        be useful as a new type of smoke
being induced to make a larger invest-       named for the fact that Furnarius cre-     detector with many applications.
ment in her offspring.                       ates nests of clay that resemble earthen
   What makes this study particularly        ovens. The nests of ovenbird species
interesting is that the basis upon which     were analyzed on the basis of 24 differ-
                                                                                        Putting Noise to Good Use
zebra finch females were choosing            ent characteristics including shape,           Still another kind of sensory ability
males as more desirable was definitely       material, and construction techniques      has now been investigated in the
not hereditary—it was the color of the       such as macerating plants, stripping       paddlefish, which seems to make use
male’s identification bands. Previous        leaves, and hollowing out trees. The       of noise to sharpen its electrorecep-
studies had shown that zebra finch           assumption was that species with simi-     tors (Collins 1999). In the 1980s, physi-
males with red bracelets around their        larly constructed nests might have had     cists developed the idea of stochastic

134 THE AMERICAN BIOLOGY TEACHER, VOLUME 63, NO. 2, FEBRUARY 2001
resonance which means that a certain         by atoms when there is uneven distri-        whale’s tongue support this view. The
level of noise can actually enhance the      bution of charge within the atom.            muscles in the tongue that are used
ability of some nonlinear systems to             The gecko’s toes are covered with        by most animals to manipulate food
detect and transmit weak signals. Since      rows of keratinous hairs called setae,       so it can be swallowed are very re-
then such phenomena have been found          with about half a million on each toe.       duced in the whale’s tongue. But the
in crayfish mechanoreceptors, in the         Each of the setae splits into hundreds       tongue does have well-developed mus-
cricket cercal sensory system that detects   of rounded ends called spatulae, which       cles connecting it to the jaw and skull,
air disturbances, and even in human          are what actually make contact with          so that it can move easily back and
muscle spindles that sense stretch. But      a surface. Engineers built a device to       forth over the throat, thus creating
in none of these cases has it been           measure the force of attraction between      suction.
demonstrated that stochastic resonance       a single seta and a surface. At first
is beneficial to the organism.               they had difficulty getting any mea-
    This situation has changed with the      surements, until they dragged the seta       Conclusion
publication of a study on the paddle-        across the surface. The force of attract-       Whales with broken jaws, beetles
fish Polyodon spathula which has pas-        ion increased dramatically when the          with smoke detectors, birds with
sive electroreceptors to detect electrical   hair was parallel to the surface. The        bracelets—is it any wonder that we
signals from its prey, the zooplankton       force detected was 10 times greater          chose biology as a career and still find
Daphnia. Researchers found that when         than expected, and strong enough that        it fascinating? When we get up in
they applied an intermediate level of        a gecko could hang from the ceiling          the morning we have another day of
noise the paddlefish were able to            by one toe. This result was particularly     wonders to look forward to, thanks
detect zooplankton over a wider range        convincing because the dragging              to the thousands of biologists who
and with increased accuracy. But this        motion used was much like that nor-          continue to spread joy by providing
research was done in a tank; what            mally found in the movement of the           fascinating new research to keep us
would be the noise source in the natu-       gecko’s feet. I think this item got so       and our students on our setae-less toes.
ral environment? It may be the plank-        much publicity not only because walk-
ton themselves. Swarms of plankton           ing across the ceiling is a notable
emit randomly fluctuating electrical         accomplishment, but because the              References
signals. This background noise could         reports were accompanied by photo-           Bergquist, D., Williams, F. & Fisher, C.
make paddlefish more sensitive to sig-       graphs of the setae and spatulae. Here         (2000). Longevity record for deep-sea
nals produced by individual plankton.        was a case where microscope photo-             invertebrate. Nature, 403, 499–500.
                                             graphs made sense to the general             Brown, K. (2000). For certain shrimp, life’s
                                                                                            a snap. Science, 289, 2020–2021.
                                             reader since they were related to a
Gecko Toes                                   phenomenon visible with the naked
                                                                                          Collins, J. (1999). Fishing for function in
                                                                                            noise. Nature, 402, 241–242.
   Several years ago while on a trip         eye. Also, the pictures, especially of the   Downs, M. (2000, June 23). Engineers join
to Hawaii, I met my first gecko. It          spatulae, were quite attractive because        biologists to gauge the gecko’s grip.
was sitting on top of the toaster when       they are graceful structures, structures       The Chronicle of Higher Education, p. A24.
                                             that adorn the feet of a particularly        Gee, H. (2000). Gripping feat. Nature,
I turned the lights on in the kitchen                                                       405, 631.
one night. Being from New York, I            graceful animal.                             Holden, C. (1999). Telling an ovenbird by
was used to roaches, but not geckos.                                                        its nest. Science, 286, 1843.
When we visited a friend’s apartment                                                      Karow, J. (2000). Atomic-force geckos. Sci-
in Honolulu the next day, there was
                                             Malformed Whales                               entific American, 283(2), 29.
                                                                                          Malakoff, D. (1999). Following the scent
another gecko climbing the wall. That’s          Not all images in biology are so           of avian olfaction. Science, 286, 704–705.
how I was introduced to this ubiqui-         attractive. A recent article on sperm        Pennisi, E. (1999a). Snakes take slow pas-
tous tropical apartment dweller. So          whales was accompanied by a photo              sage to prey. Science, 283, 623–625.
last summer, when several publica-           of a grossly malformed jaw (Pennisi          Pennisi, E. (1999c). Coming to grips with
tions ran articles on gecko toes, I was      1999c). But even though the congeni-           sperm whale anatomy. Science, 283,
                                                                                            475–477.
particularly interested (Downs 2000;         tally twisted bone was very abnormal,
                                                                                          Pennisi, E. (1999b). Snapping wings a
Gee 2000; Karow 2000; Pennisi 2000;          it came from an adult whale, one who           manakin’s serenade. Science, 283, 477.
Zimmer 2000b). It seems that for years,      had obviously managed to survive             Pennisi, E. (2000). Geckos climb by the
researchers have tried to explain how        despite this disability. And this is           hairs of their toes. Science, 288,
geckos manage to scale walls and even        hardly a unique case. A number of              1717–1718.
                                                                                              ¨
climb across ceilings so easily. Obvi-       such jawbones have been found, as            Schutz, S. et al. (1999). Insect antenna as
                                                                                            a smoke detector. Nature, 398, 298.
ously, it had something to do with           well as normal ones that have been           Van Dover, C.L. (1999). Deep-sea clams
the animal’s feet, but the search for        broken into several pieces. These find-        feel the heat. Nature, 397, 205–207.
suction cups or the presence of an           ings are somewhat surprising because         Vogel, G. (1999). Handsome finches win a
adhesive turned up nothing. Recently,        it would seem that the whale would             boost for their offspring. Science, 286, 23.
a team of biologists and engineers has       need its jaw to grasp food in order          Wikelski, M. & Thom, C. (2000). Marine
                                                                                                                                     ˜
                                                                                            iguanas shrink to survive El Nin o.
come up with a more plausible expla-         to survive. But Alexander Werth of
                                                                                            Nature, 403, 37.
nation, and it has to do with van der        Hampden-Sydney College in Virginia           Zimmer, C. (2000a). Eight if by land, none
Waals forces, one of those things that       argues that sperm whales don’t grasp           if by sea. Natural History, 109(5), 24–25.
we all learned about in chemistry class.     their food, but suck it in, and his          Zimmer, C. (2000b). Get a grip. Natural
They are the momentary forces exerted        anatomical studies of the sperm                History, 109(6), 42–43.


                                                                                                              BIOLOGY TODAY 135

								
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