How butterflies copy their neighbors to fool birds
The mystery of how a butterfly has changed its wing patterns to mimic
neighbouring species and avoid being eaten by birds has been solved by a
team of European scientists. The study is published August 14, 2011 in
the journal Nature.
The greatest evolutionary thinkers, including Wallace, Bates and
Darwin, have all wondered how butterflies that taste bad to birds have
evolved the same patterns of warning colouration.
Now for the first time, researchers led by the CNRS (Muséum National
d’Histoire Naturelle, Paris) and the University of Exeter (UK) have
shown how butterflies perform this amazing trick, known as ‘Müllerian
mimicry’.
Funded by the Biotechnology and Biological Sciences Research Council
(BBSRC), the study focused on the Amazonian species Heliconius numata,
which mimics several other butterfly species at a single site in the
rainforest.
One population of Heliconius numata can therefore feature many
distinct wing colour patterns resembling those of other butterflies,
such as the Monarch’s relatives Melinaea, which are unpalatable to
birds. This acts as a disguise, protecting them against predators.
The researchers located and sequenced the chromosomal region
responsible for the wing patterns in H. numata.
The butterfly’s wing-pattern variation is controlled by a single
region on a single chromosome, containing several genes which control
the different elements of the pattern. Known as a ‘supergene’, this
clustering allows genetic combinations that are favoured for their
mimetic resemblance to be maintained, while preventing combinations that
produce non-mimetic patterns from arising. Supergenes are responsible
for a wide range of what we see in nature: from the shape of primrose
flowers to the colour and pattern of snail shells.
The researchers found that three versions of the same chromosome
coexist in this species, each version controlling distinct wing-pattern
forms.
This has resulted in butterflies that look completely different from
one another, despite having the same DNA.
“We were blown away by what we found,” said Dr Mathieu Joron of the
Muséum National d’Histoire Naturelle, who led the research.
“These butterflies are the ‘transformers’ of the insect world.
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