Volume 6, Number 2, 1997

Musings of a mayfly maven

Twenty yards from where the White Clay Creek crosses Spencer Road, in Chester County, Pa., lies the Stroud Water Research Center, a state-of-the-art stream ecology lab built into the remains of an 18th-century barn. Water draining the nearby bucolic pastures and Wyeth-esque farmhouses trickles past the meters and flasks poised in the stream to catch its secrets. In the adjacent building, liquid scintillation counters click and whir; fluorescent orange-colored titrations drip; microscope lamps buzz.

Downstairs, a collection of water scenes by the 20th-century Impressionist Leonid lines the walls. In one painting, a bearded, balding man has been reeling in the same fish for 60 years. If it hadn't been painted 20 years before he was born, David Harley Funk, Delaware '75, could have been the model.

Funk is sitting in his office across the hall from the painting, bent over his light microscope, pushing a mayfly around a stentor dish of alcohol. Scribblings on a drawing pad document the position and number of the abdominal gills, the tarsal claws, the segments of the antennae.

Racks of glass vials the size of shotgun shells fill the desk and shelves above him. Funk's personal reference collection of hundreds of bugs from dozens of streams to compare and contrast with their cousin in the dish. It's a Eurylophella, possibly one of the four that Funk was the first to describe and name during his 20 years as-among other things-an entomologist at Stroud.

Since graduating from Delaware with a bachelor's degree in entomology and plant pathology, Funk has held two jobs. His first was as "insect zoo" curator at the Smithsonian Institution, where his collection of moths remains part of the museum's permanent holdings. In 1976, he came to work at Stroud, a field station of the academy of Natural Sciences of Philadelphia-the downtown institution that lists Charles Darwin and Thomas Jefferson among its early members. The academy is required visiting for every kid who passes through Philadelphia's public school system.

There, he is listed as staff scientist III. In reality, he is Stroud's nerve center. Rolls of cable and wire, toolboxes and testers clog the floor space of his office. Papers and blueprints detailing construction of the new $3 million lab cover the 8-by-4-foot table, "temporarily" propped in the middle of the room two years ago. From his desk, he can reach up and reprogram the new security system-altering the codes that decide who can come and go. Eighteen yellow Post-It notes frame the screen of his Macintosh computer, reminding him of things that he hasn't attended to yet.

Funk is ambivalent about the distractions. He likes to take charge, to make sure things get done right, but every interruption pulls him further away from his first love-bugs, with mayflies probably topping the list.

Ephemeroptera, or mayflies, are insects that spend most of their lives underwater, breathing through gills located on the underside of their abdomens. They begin as tiny, fertilized eggs deposited on the water surface. The eggs fall to the bottom of the stream, where specialized anchors and a sticky outer surface help to hold them in place. When the time is right-it varies by species and can be as long as 11 months-the embryo begins to develop. After a few weeks, a wingless nymph emerges to begin eating, mostly algae, and molting-shedding its external skeleton in favor of a larger, better fitting one. Anywhere from 12 to 45 molts later, a winged but sexually immature adult, a subimago, emerges from the water. One last molt and the adult imago arrives to mate, lay eggs and probably become trout food. Imagoes, often unable to feed because they lack mouth parts, live from two hours to three days; hence, the name Ephemeroptera (from the Greek epi, upon, hemera, day and pteron, wing).

Since 1986, Funk has coauthored eight scientific papers on the Ephemeroptera-most of them having to do with population genetics in which he uses genetic markers to distinguish between closely related species. Mayflies are sensitive organisms: Any change in the temperature or dissolved oxygen of a stream or the presence of a toxic substance can reduce their numbers. Consequently, they often are used as a bioassay organism-a test creature that you put in harm's way, or what you suspect is harm's way, to see how it fares.

For example, a chemical company testing a new pesticide might expose a group of mayflies to the compound to see what dose is lethal. Since even closely related species may have different requirements and a different resistance to toxics, it is essential to be able to tell them apart. But, even to the trained eye, species of the same genus can be difficult to distinguish and organisms that can't interbreed have often, mistakenly, been grouped under the same species name. Such was the case in the genus Eurylophella. Using electrophoresis, Funk was able to reclassify the group.

At the basis of the electrophoretic work is a theory of genetics called Hardy-Weinberg equilibrium (HWE). In a freely interbreeding population-all organisms are the same species-HWE holds that the ratio of the alleles [the forms of a gene controlling a given trait] will be predictable. Electrophoresis separates the alleles of individual bugs into bands that can be compared. Funk grinds up the bugs and puts them into the small wells of a special agar plate. A jolt of electricity sends the gene-encoded proteins migrating up the plate, leaving the bands in their wake. If two groups have very different band patterns, they have very different genes and thus are likely to be different species. If two groups can interbreed, a mixture of their alleles will be found in the offspring, verifying that they are the same species, even though they might look different.

Funk then correlates the genetic differences to subtle distinctions in the bodies of the organisms. For instance, he discovered the group called E. verisimilis was actually three separate species. One of the three species, which retained the name E. verisimilis, has larger head tubercles (bumps on the head that serve no known function). Of the other two, E. macdunnoughi has one short, stubby hair on the rear margin of its front legs and E. bicoloroides has a long, tapered hair in that spot.

Funk also is leaving his mark on another group of mayflies. He is in the process of applying for a patent for a species of mayfly called Cloeon. The insect wasn't genetically engineered at Stroud, but the center has collected years of data on its habits and requirements. If he is successful, genetically identical clones of the insect raised at Stroud could be sold as bioassay organisms to utilities and chemical companies. But, the mayflies remain on hold for now as the new lab construction takes priority at work.

After work, at his home in Lincoln University (it's the name of the town and the school), Funk's attention turns to terrestrial creatures.

Hiking around his house with a tape recorder in hand, he has chronicled the Musak of summer: cricket songs. Occupying a space on his Mac computer are the sonograms-the sound pictures- of nearly all the 40 or so cricket species that live in Pennsylvania. By coupling these recordings with his photographs (featured in a Scientific American article he wrote on the mating of tree crickets), he hopes to develop an audiovisual field guide for cricket mavens. "But, I haven't gotten around to it yet," he says. New additions to his family have cut into the work he used to get done at home.

Funk has given lectures on all aspects of tree crickets, mayflies and stoneflies-from photographing to curating them-at the universities of Pennsylvania, Delaware and Maine. His favorite lecture, "sex, flies and videotape," describes an unusual case of reverse sexual selection in the mating rituals of dance-flies that he was the first to document.

Males of certain species-guppies and cardinals, for instance-often are more colorful and ornate than females of that species. Darwin theorized that such characteristics evolved as a way for the males to attract a mate. In dance-flies, however, the females are the gaudier of the sexes, a rare deviation from the norm. Funk first noticed the dance-flies swarming while sitting on his back porch about 10 years ago. Since then, he has spent hundreds of hours documenting their mating rituals with notes, photos and videotape.

-Annette Heist