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Photo Marden

Jim Marden is an associate professor of biology of Evolutionary and Integrative Physiology and Behavior at Pennsylvania State University. Marden graduated from the University of Miami, before obtaining both his Master's degree and Ph. D from the University of Vermont.

Marden is interested in how animals work and why they work that way. He investigates both the mechanisms of animal physiology, and the ecological and historical reasons why particular physiological mechanisms have evolved.

Primarily interested in the physiology, behavioral ecology, life history, and evolution of aerial locomotion in insects, Marden is currently examining age-related changes in muscle physiology and thermal biology during adult maturation in the dragonfly Libellula pulchella,, the evolution of insect flight using stoneflies as model organisms, and the performance physiology of free-flying Drosophila melanogaster .


For links to this scientist's home page and other related infomation please see our resources page.

Marden responds :

4.30.01 Erik asked:
Hi, I just saw your segment on Scientific American Frontiers. I was wondering where I could find more examples of adaptation at work. More specifically, examples such as your flies that express a half or midway adaptation. Thank you for your help.

Marden's response:
Erik: First, I'll quibble with the way you have worded the question, then I will go about answering it. All organisms are adapted to their environment and to other factors that affect them (such as interactions with other members of their species), and one should probably not think in terms of "a halfway adaptation". The stoneflies that I study are perfectly adapted to moving in two dimensions across water surfaces. Evolution has no notion of progress toward a goal (it only selects for traits that provide an advantage in the present), so the concept of being "halfway" to somewhere is really just a construct of the human mind.

Enough quibbling; I appreciate the thrust of your question. You want to know about adaptations that represent possible points along the pathway between one set of abilities and another, especially when it is difficult to determine how evolution might have produced a complex trait via a gradual, incremental process. One classic example is the fossil bird Archaeopteryx, which has teeth and a bony tail (and many other traits of Theropod dinosaurs), along with wings, feathers, and certain other traits of modern birds. This odd species shows us what the intermediate stages between dinosaurs and birds might have looked like.There is a recent book about Archaeopteryx ("Taking Wing," by Pat Shipman) that you might enjoy reading.

Lungfish and other fish spend time out of water, and they have fairly rudimentary adaptations for breathing air. Legless lizards have proceeded along an evolutionary path that has made them very much like snakes. There is a really nice recent example of an evolutionary transformation at the genetic level. It involves a gene that encoded the enzyme trypsinogen, which is secreted by the pancreas, evolving in Antarctic fish so that it now encodes an antifreeze protein.

The reference is:

L. Chen et al. (1997), "Evolution of antifreeze glycoprotein gene from a trypsinogen gene in Antarctic notothenioid fish." Proceedings of the National Academy of Science 94(8):3811-6 (available on the web.)

If you want more such examples, especially in regard to behavior, I recommend a college-level textbook called:

"Animal Behavior, An Evolutionary Approach" (6th edition), by John Alcock. Another good source of information is the web site for a college-level evolution textbook.

It has some exercises and links that provide lots of information for students and teachers. It is very difficult to learn much of anything about evolution from high school textbooks. The creationists have exerted their influence on publishers so that virtually all of the material on evolution has been removed from the books.

4.30.01 Hank Jablonski asked:
If the wings of an insect are clipped to the nub, will they grow back again to its full size, or does the insect have to live with "nubby" wings and get used to living that way?

Marden's response:
Hank: No, insect wings cannot grow back. We collect (i.e. kill and keep) the insects we use in our studies, so there was never any intent to release those stoneflies. Do I feel guilty about killing a small number of insects? Nope. Just go look at how many dead insect bodies are stuck in the radiator grill of your family car. None of us stop driving in order to avoid killing insects, and we don't learn anything from the thousands each of us kills annually with our cars (prior to now you probably never even thought about them at all!).

4.30.01 Cheryl asked:
How do you know you are not causing the stone fly pain when you clip its wings? Does it have a normal life after its wings have been clipped?

Marden's response:
Cheryl: I don't know what a stonefly feels when we clip its wings. I do know that it shows no overt sign of pain, and it behaves in a relaxed and completely normal fashion after its wings have been clipped. No, they do not have a normal life after we clip their wings, because after measuring their skimming ability, we collect them (i.e. kill and keep). Thus, we never had any intent to release those stoneflies.

4.30.01 Tony asked:
I just caught the last portion of your segment, as a result, I thought I heard something along the line of 'gills evolving to wings'. If so, isn't that a large leap from gills to wings and if not, please explain.

Marden's response:
Tony: It is too big a story to tell in a 10-minute segment, or to grasp from watching only a portion of a 10-minute segment. Read my recent publication (Marden et al. 2000. "Surface-skimming stoneflies and mayflies: the taxonomic and mechanical diversity of two-dimensional aerodynamic locomotion." Physiological and Biochemical Zoology 73, 751-764.) for the full story.

4.30.01 Jamie Ringler asked:
Why do male and female dragonflies often fly in tandem pairs after they mate?

Marden's response:
Jamie: Male dragonflies stay attached to females after mating (or in some species detach but hover nearby) in order to prevent other males from rushing in and mating with that female. Males can remove sperm from previous males, so to ensure their individual reproductive success, males guard females with whom they have mated. Go sit by a pond on a sunny day this summer and watch dragonflies for awhile. You will see lots of these interesting behaviors, and some very vigorous competition among males for access to females. Wouldn't it be better for the species if the males competed less and just divided up access to females without all the competition? Sure, but contrary to popular belief, evolution does not work "for the good of the species". Read "The Selfish Gene" by Richard Dawkins for a full explanation of that puzzle.

4.30.01 Jamie asked:
What feature do scientists believe was the evolutionary precursor of wings?

Marden's response:
Jamie: There are two schools of thought. One hypothesis is that wings evolved from plate-like lateral outgrowths from the thorax. There is very little evidence to support this. The other hypothesis, which I prefer, is that wings evolved from the flapping gills of crustacean-like ancestors. There is a fairly substantial body of evidence linking insects to crustaceans, and insect wings to crustacean gills.

4.30.01 Pete Cooper asked:
Hello! I am curious about the assertion that stoneflies are flightless. As an amateur entomologist and fly fisher, I have witnessed countless thousands of stone flies in flight, of many different species. I can only assume that the stoneflies to which you refer are a particular flightless species, and I would be most interested to learn which one. Thanks for taking the time to answer my question.

Marden's response:
Pete: The species featured in the Scientific American Frontiers episode is Taeniopteryx burksii, which can in fact fly, but only if it is unusually warm (Feb - April emergence) and even then only very weakly. Another species that we have studied, Allocapnia vivipara, cannot flap its wings at all, but raises them in response to wind in order to sail across water surfaces. There are many species in the families Perlidae, Perlodidae, and Chloroperlidae that do not skim (or do so very poorly) and are fairly proficient fliers. All in all, stoneflies are a real mix in terms of flying ability, and except for the families mentioned above, nearly all are very good at surface-skimming. Check out video clips on this web site for a more complete look at stonefly skimming behaviors than what was shown on the TV show that you saw.

4.30.01 Selome asked:
Dear Jim Marden: How is it that that in evolution, an animal's genetic make-up would all of a sudden change? Are there any observations that could be shown as proof of evolution? Has any one ever observed some animals long enough to see them change?? Is there any hard proof that any way you look at it, it proves correct and can persuade people?
Selome, 11

Marden's response:
Selome: Perhaps the best "hard proof" for the process of evolution is the rapid development of drug resistance by viruses and bacteria, and insecticide resistance by insects. In many of these cases, the genetic changes responsible for the evolution of resistance have been observed and documented. It seems to me that it would be fairly easy to persuade someone dying in a hospital bed from an infection of multi-drug resistant Streptococcus bacteria that evolution has occurred. The same drugs that wiped out these bacteria two decades ago now have no effect. The drug and insecticide companies understand this. They are spending hundreds of millions of dollars on research to find new antibiotics and pesticides because they know that the ones they make now become less effective every year. They certainly are not spending this kind of money because evolution is a "theory". These are hardheaded business people who know fully well that the "fact" of evolution will put them out of business if they don't evolve their products to keep pace.

Another body of "hard proof" is the existence of all sorts of fossils that are tens or hundreds of millions of years old, and are different from any creatures that are alive today. In some cases, these fossils possess features that are intermediate between major groups of organisms (i.e. Archaeopteryx, which has both the feathers of birds and the teeth and boney tail of Theropod dinosaurs; fossil whales with small limb bones; etc., etc.)

A good source of information is the web site for a college-level evolution textbook. It has some exercises and links that provide lots of information for students and teachers. It is very difficult to learn much of anything about evolution from high school textbooks. The creationists have exerted their influence on publishers so that virtually all of the material on evolution has been removed from the books. Incidentally, despite photographs from space of a spherical Earth, there are still people who believe that the Earth is flat. See the following web site, although I get the impression that it is authored by people who are making fun of flat-earthers

Generally, regardless of how much "hard evidence" you have, it is a big waste of time to try to dissuade people from things that they have chosen to believe.

4.30.01 Christopher Adamson, Kelowna BC, Canada asked:
We were watching the April 10th show and were interested in the flies with "nub" type wings. You talk of this as an evolutionary step (wings for skimming along water instead of for flying). Are there any fossils of insects with these non-flight wings (the so-called "missing link" for insect wings from rudders)? Or is this entirely theory? Thank you for your time.

Marden's response:
Chris: I can do better than fossils. When we filmed that segment, we were studying another stonefly species in which the males have short stubby wings that they use to sail across water surfaces. This species can raise and lower its wings, but is incapable of flapping them. There are photos of this species on my web site at , a crude animation that runs across the top of my homepage at, and a movie of a long-winged female at We thought that both species would be included in the Frontiers segment, but the stubby winged sailors ended up on the cutting room floor. Since then, we have found lots of other types of surface skimming, which you can see at and One of the species that we have studied uses its wings to row along the water surface (, and this species also has what appear to be functional gills on the ventral abdomen of the adults. There are many types of fossil insects that have short stubby wings that certainly look insufficient for flying, and which also possess what appear to be gills on their abdomen (these are illustrated in fig. 7 of our recent paper: "Surface-skimming stoneflies and mayflies: the taxonomic and mechanical diversity of two-dimensional aerodynamic locomotion." Physiological and Biochemical Zoology 73, 751-764.) Thus, while we do plenty of speculation, we also have a good basis for doing so.

4.30.01 Rachelle Hill asked:
I just finished watching "Flying Free." It was quite interesting and fun, I really enjoyed it. The segment on studying bug flight spawned some ideas: first, a question, has anyone yet figured out exactly how a bumblebee flies, defying engineering? That got me thinking, why are they so hairy? Could the black hair actually trap heat, allowing the bumblebee to aid his flight with his own thermals? The reason I got onto the bumble bee question was because I noticed the scientists were studying large wings on relatively light, aerodynamic bugs. It seems to me we would be better off studying how a non-aerodynamic relatively heavy bug flies with little wings (because it seems it would give us some great tips).

Marden's response:
Rachelle: The thermal biology of bumblebees is very well known (see B. Heinrich, Bumblee Economics). The aerodynamics of insects with wingbeat kinematics similar to bumblebees has been recently described (see Dickinson et al. 1999. Science 284: 1954-1960). There are plenty of people (including the US military) who share your view that we can learn much from the aerodynamics of flying insects (see Ellington CP. 1999. "The novel aerodynamics of insect flight: applications to micro-air vehicles." Journal of Experimental Biology. 202: 3439-3448.)

4.30.01 Ankit Vachher asked:
In "Taking it to air", why was it necessary to cut only half the wings off instead of all of them? What was the purpose of cutting them off?

Marden's response:
Ankit: We trimmed the wings in order to determine if it was possible for stoneflies to skim across water using wings much smaller than those that exist in modern insects. In other words, we wanted to test our hypothesis that weight-supported aerodynamic locomotion in two dimensions (skimming across water) requires less sophisticated equipment than does true flight. It we had cut the wing off entirely, there would be no way for those insects to accomplish aerodynamic locomotion of any kind. Our hypothesis is that insect wings evolved from flapping gills of aquatic ancestors, not that insect wings evolved from nothing. Thus, we recreated approximately gill-sized wings. We also lowered the temperature so that the flight muscles produced much less power. This was our way of approximately recreating the "small" muscles that would have been used to flap the gills.

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