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                                       Net Gains
A CALIFORNIA BIOLOGIST DISCOVERED A NEW INSECT SPECIES AND THEN
                 CAUGHT EVOLUTION IN THE ACT
                     BY: DEBORAH FRANKLIN
                                          October 2002

         What a comfort it is, in this
techno-mad age, that a scientist can still
do important research in her backyard
with a butterfly net.
         Cristina Sandoval was an ecology
graduate student at the University of
California, Santa Barbara when, net in
hand, she headed into the chaparral-
covered Sant Ynez Mountains near
campus in search of a thesis. There, she
slipped the net onto various shrub and
plant branches, and then shook them to
see what fell out. Along with a dusty trove
of dried leaves, spiders, and bird
droppings, she collected an assortment of
inch-long insects that looked like beady-
eyed twigs – walkingsticks, distant
cousings of crickets and cockroaches. In
fact, she had discovered a new species of
walkingstick, which, in keeping with
taxonomic tradition, was named after
here, Timema cristane. ―I felt proud,‖ she
                                                   (Twice their normal size, a plain cristinaewalkingstick
said of the honor, adding that it gave her         prefers the ceanothus plant for blending in.)
a sense of immortality and even made her
feel protective of her six-legged namesake.        this unlikely creature for 13 years. She
         The achievement might seem                now believes that it offers a rare glimpse
quite sufficient for a scientist-in-training,      of the process that Charles Darwin
but it was only the beginning. Braving             famously called ―the origin of species.‖
poison oak, brambles, searing heat and             The evidence she has gathered suggests
rattlesnakes to observe her walkingstick           that her walkingstick, because it is so
in its scrubby habitat, baiting homemade           intensely prayed upon by lizards and
traps to learn about its predators, and            birds, is on the verge of making biology’s
teaming with other scientists to glean its         biggest leap by splitting into two distinct
genetic makeup, Sandoval has pursued               species – a phenomenon that scientists


                                       SMITHSONIAN
have long puzzled over but seldom              to the standard view of adaptation, an
observed directly.                             individual with a defensive edge is more
         "One of the biggest questions in      likely than a run-of-the-mill specimen to
biology is, how are species formed?" says      survive in a competitive bird-eat-bug
Sandoval, 41, who got her doctorate in         world and pass on its genes to the next
1993 and is now director of the Coal Oil       generation. But how does a variety
Point Reserve, a university-affiliated         distinguished only by a defense
wildlife refuge in Santa Barbara. "It’s just   mechanism evolve into a new species that
in us to want to figure out what’s going       no longer mates with members of the
on in nature to create the amazing             species from which it sprang?
diversity we see." Like other walkingsticks,             Part of the answer may reside in
the T. cristinae can’t fly, lives only a few   T. cristinae’s mating habits. A striped or
months and spends most of its daylight         plain variety tends to mate with its own
hours standing perfectly, boringly still. It   kind, Sandoval and coworkers found,
ranges across the West, Sandoval says,         even though the insects have poor
and is plumper and has shorter legs than       eyesight. The preference could be based
other walkingsticks, and the male’s            on smell, she says, or a breakdown in the
genitals are distinctive. But the main         courtship ritual. When a male
reason that Sandoval has studied the           walkingstick wants sex, he crouches on
insect so intensively is its coloration,       top of the female and tickles her
which comes in two forms and varies            antennae with his own, while stroking
according to the type of bush the insect       her abdomen with his feet. If interested,
inhabits. Those that favor the ceanothus       she’ll mate; if not, she’ll push him away.
plant, which has yellowish green oval          "Maybe males of different varieties no
leaves, are themselves plain yellowish         longer have the right equipment,"
green; they like to rest in the middle of a    Sandoval says. "Maybe they don’t do the
ceanothus leaf. By contrast, a T. cristinae    right tickle."
partial to the chamise bush, which has                   Whatever cues the insects use,
dark green, needlelike leaves, bears a         what’s important is that, somehow, the
stripe on its back and straddles a leaf. In    genes that influence mating preferences
either case, the coloration renders the        are passed along with the genes that
insect almost invisible to predators such      determine whether the walkingstick is
as blue jays and lizards, as Sandoval          striped or plain. Then predators brutishly
found in field tests. When she placed          reinforce the T. cristinae’s mating choices:
striped or plain insects on a branch from      offspring that are neither striped nor
their preferred bush, far fewer were           plain probably don’t hide well and are
gobbled up compared with those she put         easy pickings for lizards and birds.
on branches of the "wrong" bush.               Offspring that do hide well survive, mate
         That a walkingstick is living         with their own kind, and so on. If, over
camouflage is no surprise; after all, grade-   time, instances of successful
school kids study the creature as one of       interbreeding between striped and plain
nature’s more blatant examples of              varieties were to sink to close to zero,
adaptation. But Sandoval has taken the         then two species would exist instead of
phenomenon to a new level. According           one.



                                      SMITHSONIAN
        Since Darwin, biologists have           fieldwork to reveal the inner workings of
generally believed that new species form        evolution, which are usually too slow to
in nature after some singular chance            observe.
event. But Sandoval and coworkers                        Sandoval says there’s no
recently reported evidence quite to the         substitute for beating the bushes. "To be
contrary, showing that striped and plain        a good naturalist you have to go out in
varieties were popping up all over the          the field with your eyes wide open," she
hills. Working with molecular biologists        says. "You have to pay attention to
at Simon Fraser University in British           develop intuition. Analytic skills are
Columbia, she sampled DNA from                  important, and so is luck. But intuition is
several populations of striped and plain        crucial, so that you’re always ready to
walkingsticks on a Santa Ynez slope. She        pursue what luck turns up."
found that a striped and a plain
walkingstick from the same bush are             Deborah Franklin, a former senior writer for Fortune,
more closely related to each other than         covers science, medicine and culture from San
                                                Fransico.
they are to walkingsticks of similar
appearance that live several bushes away.       Read more:
Plain green and striped walkingsticks are       http://www.smithsonianmag.com/science-
continuously being born on, say, the flat-      nature/Net_Gains.html#ixzz1HqNCSzZe
leafed bush. But plain green cristinae end
up predominating because predators wipe
out most of the striped individuals.
        That’s big news to evolutionary
biologists, who have long believed that
two groups from one species would have
to be separated by vast barriers of
geography and time—an ocean or
mountain range, for example, and
perhaps thousands of years—before they
would evolve to the point where they
would not or could not interbreed. The
finding that the two visually distinct
varieties of T. cristinae arose not once, but
multiple times in bush after bush, is a
strong sign that no geographic barrier or
imponderable period of time is necessary
for speciation.
        Dolph Schluter, an evolutionary
biologist at the University of British
Columbia in Vancouver, has found
similar results in his studies of stickleback   (The striped variety seeks out the needlelike leaves of the
fish. He says the walkingstick findings are     chamise.)
"extremely cool" because they combine
DNA technology with old-fashioned



                                       SMITHSONIAN
1. What insect species has Sandoval discovered? What is its common name?




2. What is the taxonomic tradition for naming a newly discovered species?




3. Sandoval believes these insects are on ―the verge of making biology’s biggest leap.‖
   What is that ―leap‖?




4. What are the other insect relatives of this species?




5. Describe the appearance and life cycle of the insect:




6. Describe the differences between the two T. cristinae Sandoval is studying:




                                  SMITHSONIAN
7. What adaptation do these insects show to their environment?




8. How does the adaptation affect their survival and reproductive success?




9. What did Darwin believe as to how new species occurred?




10. What have modern biologist always believed were generally required for new
    species to evolve from older species?




                                SMITHSONIAN

				
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posted:11/28/2011
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