http://www.collembola.org/publicat/mimicry.htm
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Last updated on
2008.08.03
by Frans Janssens
Frans Janssens,
Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium
Introduction
Mimicry refers to the similarities between species.
Mimicry is a form of symbiosis where a species may mimic the colours,
patterns, or even behaviour of another species for one of two reasons.
Either to be able to get closer to unsuspecting prey or in the case of a
harmless species to gain protection by imitating a predator or
poisonous species.
Comparing mimicry with camouflage or deceptive behavior,
protection by mimicry is the most cost effective.
The mimicking species does not have to change its behaviour or stay against a
safe background to disguise itself.
Its appearance tell its predator to keep away.
It can go about its daily life without extra protections.
There are several described forms of mimicry utilised by both predator and prey:
Batesian mimicry, Muellerian mimicry, Wasmannian mimicry,
Peckhamian mimicry and self-mimicry.
In this short preliminary note, we will explore the possibility of a case
of a new type of mimicry in Dicyrtomina ornata
and Dicyrtomina saundersi:
the predators'-predator-mimicry.
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Fig.1. Sminthurus viridis and juvenile aphid.
Who mimics who?
Specimens from Russia, 2006.02.18.
2006 © Macroclub.ru.
Forms of mimicry
Batesian mimicry refers to two or more species that are similar in
appearance, but only one of which is armed with spines, stingers, or
toxic chemistry, while its apparent double lacks these traits.
The second species has no defense other than resembling the unpalatable
species and is afforded protection from certain predators by its resemblance
to the unpalatable species, which the predator associates with a certain
appearance and a bad experience.
Muellerian mimicry refers to two unpalatable species that are mimics
of each other with conspicuous common colouration. Thus all mimics share the benefits of the coloration since the
predator will recognise the colouration of an unpalatable group after a
few bad experiences. Since several species have the same appearance to
the predator, the loss of life will be spread out over several species,
reducing the impact on each individual species.
An example of such Muellerian mimicry in Collembola is the mimicry of
Sminthurus viridis and an aphid species (see fig.1).
Wasmannian mimicry is when the mimic resembles its host
in order to live within the same nest or structure. For example,
several jumping spiders closely resemble ants. In order to get
"lost in the crowd" and thus avoid predators.
Peckhamian mimicry, also known as aggressive mimicry,
in which the predator mimics its prey to capture it.
Self-mimicry refers to species that have one body part that mimics
another to increase survival during an attack or helps predators appear
innocuous to allow the prey extra seconds to escape.
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Fig.2. Dicyrtomina ornata
Specimen from Sussex, UK, 2006.12.10.
2006 © Cornwall, N.J.
Preliminary observation
In December 2006, and January 2007, Noel J. Cornwall keenly observed and
recorded several specimens
of Dicyrtomina ornata and Dicyrtomina saundersi
from Sussex, Britain,
that have a distinct dorsal pigment pattern
resembling the contours of an arthropodan head capsule in frontal aspect
at a larger scale (fig.2).
In dorsal view, the illusion is created that the specimen has two heads,
a small one (its true head) followed by a distinctly larger one
(a faked pseudohead).
This can be regarded as a case of self-mimicry.
However, in this case, self-mimicry has no advantadge. An attack to the
pseudohead is as vulnarable as an attack to the true head.
Therefore, self-mimicry can be excluded.
Alternatively, the dorsal pigmentation pattern
suggests that the specimen is being eaten by a larger predator.
Therefore, this dorsal pattern may mimic the head of the predator of
Dicyrtomina or even the predators' predator.
The pattern does not necessarily suggest to a candidate predator that
Dicyrtomina itself is the predators' predator.
The prey just beares a dorsal pigment pattern, its predator instinctively is
afraid of.
Mimicking the larger predator's face on its dorsum may scare away
larger sized predators.
This form of fake head mimicry might be the most ancient "photograph" of a
terrestrial predator (of the predator) of Dicyrtomina.
Dorsal mimicry of head capsule
The patched dorsal pigment pattern of Dicyrtomina ornata (fig.3)
and Dicyrtomina saundersi (fig.4) is quite distinct.
The pattern forms an illusion of a head in frontal aspect
that complies amazingly well with the head morphology of a generic hexapod.
The dark bilateral "eye patches" are distinctly visible (fig.2).
Even the "ocelli" in the "eye patches" can be seen (fig.3).
Inbetween the "eye patches", the wide clear area simulates the "vertex".
The "antennae" can be recognised in front of the "eye patches",
bent in an exad way.
More below, a light coloured patch simulates the "clypeal area".
And below that, the "labrum" with protruding "mouthparts" is easily recognized.
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Fig.3. Dicyrtomina ornata
Specimen from Sussex, UK, 2006.12.05.
2006 © Cornwall, N.J.
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Fig.4. Dicyrtomina saundersi
Specimen from Sussex, UK, 2007.01.03.
2007 © Cornwall, N.J.
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More observations of posterior dorsal mimicry
Also the characteristic posterior dorsal patch of Dicyrtomina species,
when observed from caudal aspect,
distinctly mimics the head of an arthropod in frontal aspect.
The genito-anal abdominal segments suggest a clypeus and labrum,
while the long apical anal setae mimic external mouthparts and/or their sensilla.
The pale coloured bilateral patches mimic large compound eyes.
An equally sized predator, sneaking on a specimen of Dicyrtomina
from behind, will surprisingly 'face' a seemingly larger possible competitor.
Dicyrtomina, caudal aspect.
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Fig.m1. D. ornata from the UK,
Sussex
2006 © Cornwall, N.J.
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Fig.m2. D. ornata from the UK,
Worthing
2007 © Valentine, B.
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Fig.m3. D. ornata from the UK,
Worthing
2007.11.30 © Valentine, B.
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Fig.m4. D. ornata from the UK,
Worthing
2007.12.15 © Valentine, B.
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Fig.m5. D. ornata from the UK,
Surrey
2007.12.16 © Barton, T.
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Fig.m6. D. saundersi from the UK,
Dudley
2007.12.29 © Campbell, A.
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Fig.m7. D. saundersi from the UK,
Surrey
2008.01.12 © Barton, T.
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Fig.m8. D. ornata from France,
Saint Pierre d'Oléron
2008.02.12 © Lavoué, B.
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Fig.m9. D. saundersi from the UK,
Cheshire
2008.04.30 © Farrell, S.
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Note the variability in the shape of the posterior dorsal patch in the
geographically different populations, possibly induced by the presence of
available local predators. Specimens that mimic the head of the local predators
better than others will have an advantadge to survive and will eventually be
selected out.
To be completed.
The mimicked Collembola predators
The dorsal mimicry imposes the question: "What kind of predators are represented
at the dorsum?"
Two alternative hypotheses:
1. the dorsal mimicry represents an ancestral terrestrial crustacean predator of Collembola,
2. the dorsal mimicry represents a more recent hexapod predator of Collembola.
The dorsal mimicry represents an ancestral terrestrial crustacean predator
In this hypothesis, the mimicry represents an early terrestrial crustacean
arthropod that predated on Collembola, at least 400 million years ago.
The mimicry preserves the face of a predator that co-existed with the
Collembola in the Devonian, when the Collembola were at their evolutionary
climax.
The dorsal mimicry represents a more recent hexapod predator
This hypothesis complies with the phylogeny that claims that Symphypleona
are the most recent Collembola.
Dicyrtomina is a more recent type
of Collembola, and the mimicry might represent a more recent hexapod predator,
possibly an Orthoptera.
This hypothesis is supported by the observed variability in the shape of the
posterior dorsal patch. That the patch shape is not constant in geographically
different populations might be an
indication of the still ongoing natural selection mechanisms
in function of available predators.
Conclusion
The mimicry can be interpreted as a kind of snapshot of a specific
predator of Collembola.
Actually, it represents one of the very first genetically induced "photographs".
