The Unsorted BBS Collection/thegreatunsorted.tar/thegreatunsorted/texts/term_papers/imposter.esy

Text File | 1988-02-22 | 9KB | 140 lines

                        THE GREAT IMPOSTERS

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.