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Avoiding Attack: Design and Deception in Nature, presented by Tom Sherratt, Carleton University

October 2011

“Avoiding Attack: Design and Deception in Nature” presented by Tom Sherratt, Carleton University

Creatures evolved to survive in the natural world: a report of the October 2011 lecture, written by Joel Byrne

The lights go down, the shuffling and conversations stop and I hear myself whispering: “This is going to be another great talk.” And so it was as the Mississippi Valley Field Naturalists (MVFN) public lecture series continued October 20th with the presentation, “Avoiding Attack: Design and Deception in Nature.”

The guest speaker, Dr. Tom Sherratt from Carleton University’s Biology Department, would be comfortable being described as an ‘evolutionary biologist’, in that his “primary interest is in how natural selection has acted, and continues to act to produce organismal traits.” His research interests, both theoretical and experimental, are in evolutionary ecology. He quickly outlined the solutions animals have evolved to avoid being attacked by predators in the natural world.

The first of these, and most obvious, is to avoid detection. Fortunately for potential prey animals there are a good number of ways to disguise themselves. Crypsis, or matching your background, sure challenges a predator. So does masquerading. The science behind this was explained using the Winnie the Pooh and the honey tree story (in which Pooh tries to fool the bees by pretending to be a little black rain cloud). Disruptive patterns break up your shape. Disruptive colouration can also do the trick. Dr. Sherratt’s lab researchers went out looking for Yellow-Banded Underwing Moths and Carpet Moths on trees to see if the way they rested on the bark, vertically, horizontally, or somewhere in between reduced their rate of being attacked. They discovered that the best way to survive if you’re an Underwing is to hang on vertically and head down and this is what they do. Orienting yourself with the bark worked better for Carpet Moths. Just remember—camouflage is good; without it, you’d better find another strategy.

Develop a defense and advertise it! That is use ‘warning colours’, develop spines, get a stinger, or develop a toxin. A classic example is the poison arrow frog with its toxicity and very bright warning colours, raising the big question, why do warning signals tend to be conspicuous? And, Dr. Sherratt asked, “Do invertebrate predators pay attention to warning signals?” To answer this the lab researchers tempted dragonflies with wasps, hover flies, bees and flies attached to sticks. The dragonflies attacked one and all, not paying attention to black and yellow markings or any other warning signs. Instead they seemed to be very size-selective about their potential prey, choosing the smaller flies and bees.

But what if you, the prey, have no defenses from predators? This brings up the third solution that Dr. Sherratt illustrated with more fascinating images: Look like something defended. In other words be a mimic. If you’re an edible species, ‘the mimic’, evolve to resemble an inedible one, ‘the model’. Thus the prey species gains a degree of protection from predators by resembling an unpalatable or otherwise defended species. This is Batesian mimicry, named after Bates a contemporary of Charles Darwin. Consider hover flies, of which there are many species. They so resemble bumble bees and wasps that they have played a key role in debate about ‘perfection’ in mimicry. Another kind of mimicry, Műllerian mimicry, named after Műller, also a contemporary of Darwin, occurs when ‘an unpalatable or venomous species resembles another of the same.’ Sound familiar? These two kinds of mimicry (Batesian and Műllerian) were brought to our attention to illustrate that distinctions between different kinds of mimicry might not be that clear cut. There can be overlap, grey areas, mistakes can be made, and myths can grow. A case in point is the Viceroy Butterfly’s resemblance to the Monarch Butterfly. This was thought to be a great example of Batesian mimicry— the Viceroy a tasty (to birds) species resembling an unpalatable monarch and thus avoiding attack. But it has been discovered that the viceroy is toxic but still more edible than the monarch to some birds, Blue Jays and Red-winged Black birds, for example. Thus the viceroy butterfly is now generally classed as a Műllerian mimic of the monarch. Since both monarchs and viceroys get eaten it seems to be to their mutual benefit to stay toxic, resemble each other, and share the burden of teaching predators to not eat too much of either one. If this is too complicated a solution, a prey species can, like members of one fly family, adapt to look like wasps and pretend to actually sting would-be predators. Other kinds of mimicry were discussed including sexual mimicry accompanied by more illuminating images.

wasp mimic sherratt lecture (640x480)

“Consider hoverflies . . .” said Dr. Sherratt during his natural history lecture. They so resemble bumble bees and wasps that they have played a key role in debate about ‘perfection’ in mimicry. This photo shows, not a wasp, but a hoverfly of the family Syrphidae. MVFN file photo courtesy Dr. Henri Goulet

Dr. Sherratt wound up his talk with a quiz. He showed an image of wasp mimics, eighteen insects of various taxa all on one page, and asked which ones were wasps. Some of the look-a-likes were bees, some flies and so on, but picking out the wasps was tough. There were only four in the whole bunch. No one guessed correctly but one or two in the audience were close. Very humbling. After the talk, Dr. Sherratt fielded questions from the crowd. There were lots of good questions—a sure sign that the talk was well received. I found a great source of further insight into these questions and more, in a book entitled Avoiding Attack-The Evolutionary Ecology of Crypsis, Warning Signals and Mimicry co-authored by our speaker Thomas Sherratt, Graeme Ruxton and Michael Speed. Dr. Sherratt asked some of the Big Questions in evolution in his talk which only wetted our appetites for more big questions. Fortunately we can get some relief from this hunger in another of his books Big Questions in Ecology and Evolution co-authored with David Wilkinson.

E.T. Seton, in his book Two Little Savages, wrote a one-sentence preface as follows: “Because I have known the torment of thirst I would dig a well where others may drink.” He was referring to his “torment of thirst” for knowledge of the natural world. Tom Sherratt gave us a hearty drink from his well. Go on-line for Dr. Sherratt’s lab, website and email. One of Dr. Sherratt’s doctoral candidates, one Tom Hossie, has a caterpillar of the day blog about caterpillars & their eyespots. One actually appears to wink!

Joyce Clinton and Tom Sherratt (1280x1001)

Evolutionary Biologist Tom Sherratt (right) receives enthusiastic thanks from MVFN President Joyce Clinton at the conclusion of his MVFN talk on design and deception in nature. Photo by Pauline Donaldson






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Avoiding Attack: Design and Deception at next MVFN Lecture

Press Release

Avoiding attack: Design and Deception in Nature at next MVFN lecture

by Cathy Keddy

Bird-dropping moth photographed in Almonte by P. Donaldson

The Mississippi Valley Field Naturalists’ (MVFN) public lecture series, Trends in Fauna and Flora, continues October 20 with the second presentation, “Avoiding Attack: Design and Deception in Nature” with guest speaker Dr. Tom Sherratt from Carleton University. You do not need to be an expert to enjoy these presentations—just possess a curiosity or appreciation for wild nature. Cottagers, hunters, fishermen, canoeists, hikers, campers, artists and seasoned field naturalists alike will find something to interest them as we explore what lives in Lanark County and how best to protect it for future generations. Refreshments are offered at each lecture.

 Dr. Sherratt will talk about crypsis (camouflage), warning signals and mimicry in nature—a diverse array of mechanisms that many organisms have evolved to avoid attacks from predators. He has studied these interesting and effective survival strategies in many different species including birds, butterflies, fungi, and dragonflies, and has also published a book on the subject.

 Do you remember learning about peppered moths in England in connection with the Industrial Revolution and how the dark form of the moth became more abundant than the peppered (black and white) form because it could hide on soot-covered tree trunks? Well, this is only part of the cryptic story for these moths…It turns out that the peppered form is hidden from birds (which can see ultraviolet light) when resting on crustose lichens (both moth and lichen reflect UV light), but not when resting on foliose lichens (these lichens do not reflect UV light but the moth does). To us however, being unable to detect UV light, the moths appear camouflaged on both lichen types!

 Mimicry in nature seems unlimited. Flies pretending they are bees—done so well, even professional entomologists may file specimens in the wrong drawer. Or consider sexual mimicry in damselflies—30-90% of females (in some species) want the males to think they too are males to avoid harassment. There are moth larvae that look like twigs and moths that look like leaves. Some moths even look like bird droppings. An example is the aptly named ‘bird-dropping moth.’ Mimicry comes in many forms including shape, odour, taste, sex, sound, movement, or colour. All reflect the ability of predators to perceive and prey to deceive.

 Why are warning signal colours in nature (in our eyes) yellow and black? Why not red and blue? Why don’t more prey species sport these colours? Rather than wonder why a particular organism does not seem to be wearing warning colours, or does not appear to be cryptic or be using mimicry, we should consider first what sorts of predators the organism is at most risk from, and then think about that predator’s sense perceptions. Also remember… our appreciation of predator-prey communication is hampered by our own limited sensory perceptions of nature.

In the fascinating natural world, just as in our society, there is likely far more deception than we realize. Dr. Sherratt will tell us more at his MVFN presentation “Avoiding Attack: Design and Deception in Nature,” at 7:30 pm, Thursday, October 20, 2011 at the Almonte United Church, 106 Elgin St., Almonte. All are welcome ($5 fee for non-members). For further information please contact MVFN’s Program Chair Cathy Keddy at 613-257-3089.


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