The "holstein" (because of its black and white
markings) butterfly has a very complex relationship with
its environment. It depends on the caterpillar foodplant
which in Belize is the rare passionvine Passiflora pittieri.
No other Belizean passionvine
species is capable of feeding the caterpillars of the Holstein.
This passionflower has the habit of growing at very irregular
intervals and most of the year there is no young growth
available. The holstein caterpillars however, can not eat
old leaves!
How the holstein butterfly has overcome this problem is
an interesting story which has become one of the text book
examples of co-evolution. The key in this story is the Cucurbid
vine Psiguria
warscewiczii. This vine and the butterfly have virtually
become dependant on each other (mutualism).
The players:
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The
Passionvine: Passiflora pittieri is
one of the rarer passionflower species in Belize.
It occurs from Belize southward into South America
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The
butterfly: Heliconius sapho is black and white
but has a blue metalic sheen when seen under the right
lighting conditions.
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The
cucurbid vine: Psiguria warscewiczii
is a slender vine in the rainforest. The flowers are
very small and the plant usually goes unnoticed.
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The story
below is a simplified vision of how this relationship
came to be. The reality of action and reaction is
much more complicated and involved many more steps
and even players.
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Heliconius
butterfly lays eggs on passionvine
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Passionvine
develops toxins to deter herbivores such as Heliconius
caterpillars.
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Heliconius
develops the ability to deal with toxins in passionvine.
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Passiflora
speciation leads to differences in toxicity, toxin
levels etc.
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Each
species becomes highly specific to its host-passionvine.
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Heliconius
sapho caterpillars can not deal with toxin levels
in mature leaves. They can only eat immature leaves
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Passiflora
pittieri plants spends long periods in “growth-
inactivity”, but produces massive young growth at
long intervals
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Heliconius
sapho is faced with long periods in which it can
not lay eggs because the foodplant is not producing
young growth
Only
way to overcome this dilemma is by staying alive a
long time.
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Psiguria
vines are visited by the butterflies for pollen.
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By
developing the ability to eat pollen (nutritious food),
the butterfly can now live for up to 6 months and
wait for the next young Passiflora shoot to
appear
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Psiguria
vines develop small flowers forcing the butterflies
to visit many flowers, thus increasing chances for
cross-pollination.
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Butterflies
live long, have a good memory and good eyesight. They
learn to locate both Passionflower and Psiguria
and visit them on a daily basis to inspect for young
shoots / flowers with pollen.
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Passiflora
pittieri vine starts to form a large young shoot
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Psiguria
continuously produces male flowers. By becoming a
reliable pollen source they guarantee daily visits
from pollen feeding (but also pollinating butterflies.
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Butterfly
lays large number of eggs as the shoot just develops.
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The
eggs do not hatch for a relatively long time. Meanwhile
shoots expand.
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Heliconius
butterflies only visit male flowers because female
flowers do not have pollen. Psiguria vine
becomes all-male. Occasionally a single plant changes
sex and produces female flowers.
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Eggs
are timed to hatch when the amount of young leaf has
expanded enough to support the large number of caterpillars
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Butterfly
expects to find male flower with pollen, but no pollen
is available.
While
attempting to find pollen in this flower, it inadvertently
leaves pollen behind that was gathered during visits
to other flowers
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Pollination
takes place
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Fruit
forms
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Psiguria
vine returns to the male phase in order to keep Heliconius
butterflies interested.
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