Download Monarch, Viceroys and Queens

4A: Monarch/Viceroy Case:
Handout
Monarchs, Viceroys and Queens: Who’s the real pretender to the throne?*
by Christopher Majka
from The New Brunswick Naturalist
Biology, like any scientific discipline, is constantly being revised in light of new findings and
results. Seldom, however, is the “apple cart” so completely upset as is currently the case with the
delightful and fascinating science of mimicry.
Henry W. Bates, the English naturalist and explorer spent a decade in the middle of the
nineteenth century wandering the jungles of the Amazon avidly pursuing what biologist Richard
Lewontin has called “the genteel upper-middle-class fascination with snails and butterflies.” As a
result of his exploration, in 1862 Bates published an article, Contributions to an insect fauna of
the Amazon Valley, in Transactions of the Linnean Society. This article gave rise to a new study
in biology – mimicry.
Bates captured over one hundred species of butterflies, many of which, even though they came
from different lineages, showed a striking resemblance to one another. The theory (model), as
elaborated by more recent findings, states that certain butterflies have evolved a chemical
defense system that protects them from predators. They have also evolved a distinctive
coloration to warn off possible predators. Experiments confirm that birds, after they have
attacked such a butterfly, will be less likely to try and eat it again. Thus the coloration acts as a
warning flag.
In some instances, other species mimic this warning coloration. By resembling the distasteful
species they may avoid being eaten by animals who have learned the warning signal. This,
however, has some disadvantages for as R.I. Van-Wright states “Bluff with no stick to wield when
challenged, is a risky sort of defense.” (A case of self deception in Nature 350: 460-46, 1991) If
there are too many mimics then potential predators get conflicting information, possibly even
taking the “warning flag” for a “dinner bell.”
Further evidence to support the mimicry model came from the fact that many of the “distasteful”
butterflies feed on toxic plants – Milkweed, Nightshade, etc. It was assumed that the larvae of
such butterflies, which somehow were not affected by the toxins, were able to “stock-pile” the
chemicals in their bodies and keep them through to the butterfly stage of their lives. The larvae of
the mimic species, on the other hand, were usually found to feed on non-toxic plants. This
evidence supports the mimicry model as developed by Bates!
Ever since the studies of Jane Van Zandt Brower in the mid 1950’s (Experimental studies of
mimicry in some North American butterflies. Evolution 35:32-47, 1958) the Monarch and the
Viceroy have been considered to be classic examples of “Batesian” mimicry.
Now, however, standing the current model on its head, new findings suggest that this whole
scenario, and all that we once believed about mimicry “ain’t necessarily so.” David Ritland and
Lincoln Brower challenged the model in 1991 (The viceroy butterfly is not a batesian mimic.
Nature 350: 497-498). In their study of Monarchs, Viceroys and Queens (a close relative of the
Monarch) they offered Red-winged Blackbirds the abdomens of all three species, as well as
abdomens of non-toxic control butterflies. They gave the birds only abdomens to prevent them
from seeing the “warning” colors of the wings. Thus the birds could only respond to the taste of
the butterfly. To their surprise they found that the Viceroy and Monarch were both equally
distasteful to the birds (only 40% eaten of both as compared with 98% of the control butterflies).
This was supported by other measures that they studied. In one fell swoop the basis for
supporting Batesian mimicry between these species disappeared.
Not all is lost, however. A few years after Bates, a German biologist, Fritz Muller also went
collecting butterflies on the Amazon. In his paper, Ituna and Thyridia: a remarkable case of
mimicry in butterflies (Proceedings of the Entomological Society of London, 1879: 20-29), he
argued that if all the toxic species of butterflies have their own warning coloration pattern that
predators would have to learn every one – with a similar number of fatalities and mutilations to
each species of butterfly. Now, he argued, if several toxic species have the same pattern then
they both benefit. Predators only have to learn one color pattern. This type of mimicry is called
Mullerian and it seems that the relation between Monarchs and Viceroys may be an example of it.
At this point you might be tempted to say “so what?! Mullerian mimicry, Batesian mimicry, mimicry
is mimicry!” In fact from an evolutionary and ecological perspective these two forms of mimicry
are very different for both predator and prey. Mullerian mimics, for example, are in the process of
becoming more alike over time, while Batesian mimics are likely to become less alike.
Other research is also challenging our traditional models of mimicry. Work done by K.S Brown,
Jr. (Revista Brasileria de biologia 44: 435-460, 1985) has shown that many toxic butterflies obtain
little or no toxic chemicals from the plants on which their larvae feed. In fact Ackery (Hostplants
and classification: a review of Nymphlid butterflies. Biological Journal of the Linnean Society 33:
95-203, 1988) has proposed that the relationship between the plant and the butterfly is quite
different. He argues that butterflies often evolve their own chemical defenses and only then do
they shift to feeding on plants that are also toxic. Depending on the species, the butterflies may or
may not accumulate the chemical from the plant, as the Monarch appears to.
Some researchers doubt that Batesian mimicry exists, rather they argue that all such
relationships can be found along a range of Mullerian mimicry. Others argue that, because all
species involved in Mullerian mimicry are distasteful, they are not mimics at all. In other words,
mimicry, as such, might not even exist!
*This reading has been edited to better match the terminology used in the natural selection unit.