Spring 2001 -- Vol. 18, No. 1

Extreme Adaptation and Development Found Among Animals and Insects
as well as Microscopic Organisms

He knows dragonflies are not extremophiles.  After all, they're insects--and insects get so little respect that even agencies that fund research set no rules for their ethical treatment.

Still, to Jim Marden, associate professor of biology, dragonflies are special because they represent an extreme form of development.  No other organisms invest more body mass purely for the purpose of flight than dragonflies.  Flight muscles account for up to 63 percent of a male dragonfly's body mass.

"That doesn't leave a lot in the other 37 percent, which includes the mass of the wings, exoskeleton, and eyes," Marden says.  "There's not a lot of room for digestive, circulation, excretory, and reproductive organs.  We're trying to discover what evolutionary forces pushed them into a form that is almost all engine and almost no payload."

Along with his research on dragonflies, Marden studies the evolution of flight in other insects.  His work requires abundant field research and allows him to learn a great deal about specific types of insects and the development of their flight.

In terms of dragonflies, he knows only the males of the species develop such a large amount of flight muscle.  Females maintain a fairly constant muscle mass of about 40 percent of their body weight throughout their lifetimes, with most of their growth occurring in ovaries rather than muscle.  While male dragonflies also begin life with about 40 percent of their body mass devoted to flight muscle, their growth occurs primarily in their flight muscles, which gives them strong flying skills for attracting females and conducting aerial battles against other male dragonflies.  After enduring such battles and spending a day or two guarding an area of a pond or other potential breeding area long enough to fertilize eggs deposited by females, male dragonflies disappear from the scene.

"They have a one-way trajectory," Marden says.  "They build and build, get to the stage to fight and mate . . . and then flame out.  In our field work, we do not see them again after they've done all that."

How and why dragonflies develop as they do provides the real mystery, though, and it is one Marden hopes to solve.  He's looking for answers on a cellular and molecular level and hopes his work can be applied to understand more than just the bulked-up dragonflies.  Like Marden, many scientists believe microscopic extremophiles and larger animals that survive at environmental or evolutionary extremes provide an important resource as a potential source of information.

Although Marden knows his dragonflies do not meet the typical definition of extremophiles, some animals do blur that line of distinction--like those living at hot vents and cold seeps on the ocean floor studied by Charles Fisher, professor of biology.   While microscopic bacteria might survive at temperature extremes of about 115 to 120 degrees Celsius (about 245° F), some hydrothermal vent animals survive in water as hot as 80 degrees Celsius (176° F).  Still others live on cold methane ice.

"The real extremophiles, the ones who can take the very highest temperatures, the very worst conditions, and the least oxygen . . . those are all bacteria," Fisher says.  "Real animals can thrive in some pretty extreme areas, though.  Plus, because they're multicellular, animals have adaptation options that are not open to bacteria."

Some animals have adapted to deal with limited-oxygen environments and others somehow survive in the presence of extremely hot water, in some instances having that water touch their bodies for brief periods of time.  Even among the same species, such as tube worms Fisher specializes in, the adaptations and differences can be striking.  For example, tube worms at thermal vents live hard and die young.  In the nutrient-rich, quickly changing environment, they have adapted to grow and reproduce very quickly during their typically short lives.  At cold seeps, other tube worms--almost the same animal with similar blood and similar symbionts--live a rather laid-back lifestyle, growing slowly and living longer than any other animals on the planet.

"Anytime you have animals or bacteria in an extreme, you can learn something from them," Fisher says.  "There are reasons they survive, even thrive, where they live and we can apply what we find out about them to other research areas and learn things that might directly help the human race."
As a result, groups such as NASA, the National Science Foundation, and biotechnology firms strongly support research designed to learn more about such animals.

-- By Steve Sampsell

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