Essay/Term paper: The great imposters

Essay, term paper, research paper:  Science

Finding good day
care can certainly pose a problem these days,
unless, of course, you're an African widow bird.
When it comes time for a female widow bird to lay
her eggs, she simply locates the nest of a nearby
Estrildid finch and surreptitiously drops the eggs
inside. That's the last the widow bird ever sees of
her offspring. But not to worry, because the
Estrildid finch will take devoted care of the
abandoned birds as if they were her own. And
who's to tell the difference? Though adult widow
birds and Estrildid finches don't look at all alike,
their eggs do. Not only that, baby widow birds are
dead ringers for Estrildid finch chicks, both having
the same colouration and markings. They even act
and sound the same, thus ensuring that the widow
bird nestlings can grow up among their alien
nestmates with no risk of being rejected by their
foster parents. MASTERS OF DISGUISE Things
aren't always as they seem, and nowhere is this
more true than in nature, where dozens of animals
(and plants) spend their time masquerading as
others. So clever are their disguises that you've
probably never known you were being fooled by
spiders impersonating ants, squirrels that look like
shrews, worms copying sea anemones, and
roaches imitating ladybugs. There are even animals
that look like themselves, which can also be a
form of impersonation. The phenomenon of
mimicry, as it's called by biologists, was first noted
in the mid-1800s by an English naturalist, Henry
W. Bates. Watching butterflies in the forests of
Brazil, Bates discovered that many members of
the Peridae butterfly family did not look anything
like their closest relatives. Instead they bore a
striking resemblance to members of the
Heliconiidae butterfly family. Upon closer
inspection, Bates found that there was a major
advantage in mimicking the Heliconiids. Fragile,
slow-moving and brightly coloured, the Heliconiids
are ideal targets for insectivorous birds. Yet, birds
never touch them because they taste so bad.
Imagine that you're a delicious morsel of butterfly.
Wouldn't it be smart to mimic the appearance of
an unpalatable Heliconiid so that no bird would
bother you either? That's what Bates concluded
was happening in the Brazilian jungle among the
Pieridae. Today, the imitation of an inedible
species by an edible one is called Batesian
mimicry. Since Bates' time, scientists have
unmasked hundreds of cases of mimicry in nature.
It hasn't always been an easy job, either, as when
an animal mimics not one, but several other
species. In one species of butterfly common in
India and Sri Lanka, the female appears in no less
than three versions. One type resembles the male
while the others resemble two entirely different
species of inedible butterflies. Butterflies don't
"choose" to mimic other butterflies in the same
way that you might pick out a costume for a
masquerade ball. True, some animals, such as the
chameleon, do possess the ability to change body
colour and blend in the with their surroundings.
But most mimicry arises through evolutionary
change. A mutant appears with characteristics
similar to that of a better protected animal. This
extra protection offers the mutant the opportunity
to reproduce unharmed, and eventually flourish
alongside the original. In the world of mimics, the
ant is another frequently copied animal, though not
so much by other ants as by other insects and
even spiders. Stoop down to inspect an ant
colony, and chances are you'll find a few
interlopers that aren't really ants at all but copycat
spiders (or wasps or flies). One way you might
distinguish between host and guest is by counting
legs: Ants have six legs while spiders have eight.
Look carefully and you might see a few spiders
running around on six legs while holding their other
two out front like ant feelers. COPYCATS
Mimicry can not only be a matter of looking alike,
it can also involve acting the same. In the
Philippine jungle there is a nasty little bug, the
bombardier beetle. When threatened by a
predator, it sticks its back end in the air, like a
souped-up sports car, and lets out a blast of
poisonous fluid. In the same jungle lives a cricket
that is a living xerox of the bombardier beetle.
When approached by a predator, the cricket will
also prop up its behind -- a tactic sufficient to
scare off the enemy, even though no toxic liquid
squirts out. Going one step further than that is a
native of the United States, the longicorn beetle,
which resembles the unappetizing soft-shelled
beetle. Not content to merely look alike, the
longicorn beetle will sometimes attack a
soft-shelled beetle and devour part of its insides.
By ingesting the soft-shelled beetle's bad-tasting
body fluid, the longicorn beetle gives itself a
terrible taste, too! Protection is by no means the
only advantage that mimicry offers. Foster care
can be another reward, as proven by the African
widow bird. And then there's the old
wolf-in-sheep's-clothing trick, which biologists call
aggressive mimicry. The master practitioner of
aggressive mimicry is the ocean-going anglerfish.
Looking like a stone overgrown with algae, the
anglerfish disguises itself among the rocks and
slime on the ocean bottom. Protruding from its
mouth is a small appendage, or lure, with all the
features of a fat, juicy pink worm. The anglerfish
lacks powerful teeth so it can't take a tight grip on
its prey. Instead, it waits motionless until a small
fish shows interest in the lure, and then wiggles the
lure in front of the fish's mouth. When the small fish
is just about to snap at the lure, the angler
swallows violently, sucking the fish down its hatch.
Diner instantly becomes dinner. SEXUAL
IMITATORS Of all the many impostures found in
nature, probably the sneakiest are those of the
sexual mimics: males who imitate females to gain
an advantage at mating time. Here in Ontario we
have a sexual mimic, the bluegill fish. Male bluegills
come in two types: the standard male and the
satellite male, which looks just like a female
bluegill. In preparation for mating, the standard
male bluegill performs the job of building the nest,
where he bides his time until a female enters it to
spawn. Satellite fish don't build nests, choosing
instead to hover around the nest of a standard
male until the moment when a pregnant female
enters. The satellite fish follows her into the nest,
deceiving the nestbuilder into believing that he is
now in the presence of two females. The three fish
swim around together, and when the female drops
her eggs, both males release a cloud of sperm.
Some of the eggs are fertilized by the resident
male, some by the satellite male, thus passing on
passing on different sets of male genes to a new
generation of bluegills. Another case of sexual
mimicry has recently been uncovered in Manitoba
among the red-sided garter snakes. The little town
of Inwood, Manitoba and the surrounding
countryside is garter snake heaven, where you can
find the largest snake colonies on Earth. Every
spring, the red-sided garter snake engages in a
curious mating ritual. Soon after spring thaw, the
males emerge first from their winter cave and
hover nearby. The females then slither out a few at
a time, each one exuding a special "perfume"
which signals to the fellows that she's ready to
mate. At first whiff of this lovely odour, a mass of
frenetic males immediately besieges the female,
wrapping her up in a "mating ball" of 10, 20 or
sometimes as many as 100 writhing males, all
hoping to get lucky. Scientists have now
discovered that some male red-sided garters give
off the same perfume as the female, and they do
this while intertwined in the mating ball. Male and
female red-sided garters look exactly alike, so the
male with the female scent can effectively distract
many of the males from the real female, giving the
imposter a better shot at getting close to the
female and impregnating her. Males passing as
females, fish as bait, beetles as ants -- amidst all
this confusion, it still sometimes pays to just be
yourself, which could certainly be the motto of the
amazing hair-streak butterfly family. Decorating
the hair-streak's lower hind wings are spots that
look like eyes, and out-growths that look like
antennae, creating the illusion that the butterfly has
a second head. Whenever the hair-streak alights, it
jerks its dummy antennae up and down while
keeping its real antennae immobile. Presumably,
this dummy head exists to distract predators. If so,
we finally have the first scientific proof that two
heads are better than one.