June 23, 2003

Altizer gives butterflies the royal treatment

By Eric Rangus

Although one of the most common butterflies in North America, the monarch’s vibrant orange and black wings make it distinct and instantly recognizable. But within that distinction may hide a great deal of variation. Just how much variation is what Sonia Altizer wants to find out.

This summer Altizer, assistant professor of environmental studies, is researching four populations of North American monarchs to determine whether they vary in development, survival, growth rate, color and size, among other factors. She is currently studying the effect of temperature on their color patterns and development.

Monarchs, which can be found on four continents, are tropical in origin, and two of Altizer’s populations are from warm-weather climates: Hawaii and South Florida. The other two are migratory populations, originating in the eastern and western United States and Canada. Each winter, these populations—from 50 million to more than 100 million butterflies—travel up to 2,000 kilometers to Mexico and California.

It is that birdlike migration that makes the monarchs special, and investigating the differences between the migratory and nonmigratory butterflies is a prime goal.

“My approach has been to look at traits that might vary in response to selection,” said Altizer, adding that monarch populations are similar genetically. “Chances are you would see differences in their environment, host-plant species, natural enemies and other factors.”

Most of Altizer’s butterflies are descended from insects caught in the wild, and beautiful though they are, catching monarchs is not glamorous work. A lot of it involves standing next to the road with a big net dodging speeding trucks. Since milkweed, the monarchs’ preferred meal, often grows in ankle-high water, slogging through ditches also is a big part of it.

If pickings are slim, Altizer and members of her lab are not above going to nurseries and plucking caterpillars off milkweed plants. The monarchs populating Altizer’s lab now are two generations removed from a group of about 200 butterflies caught in the wild last spring.

Nick Vitone, one of Altizer’s research technicians, caught butterflies in Hawaii; undergraduate lab technician Bethany Farrey caught them in Florida; and Altizer herself went butterfly hunting in the Atlanta area and, with Vitone, in California.

The original butterflies have since died, and now researchers in Altizer’s lab are raising their progeny, which are bred in a greenhouse on the Michael Street parking deck and stored in her lab in the Math & Science Center. When the adult monarchs emerge from their cocoons, the size, shape and color of their wings will be measured; they also are weighed and their pigmentation checked among other measurements. One of the variables is temperature; each population will have members living in hot, medium and cold environments. After the butterflies die, they are stored in thick binders, each page a mosaic of almost-identical wings.

Each butterfly has an identification number on its wing. Although the insects look fragile, they actually are quite hardy and can withstand a great deal of handling without harm. In addition to the numbering, butterflies are placed on a scanner so their wings can be photographed.

The computer analysis they undergo allows for a much more sophisticated investigation into the differences between the populations. The naked eye can only see so much, but the computer can analyze the data in a multitude of ways. Once the data are collected, Altizer and research coordinator Andy Davis compare the populations.

One early finding is that the tropical, nonmigratory butterflies appear to have darker wings, which was unexpected, since lighter coloring is usually more common in warm-weather creatures.

Altizer first began studying monarchs while a graduate student at the University of Minnesota. Her advisor had asked that she find out what sort of parasite was responsible for killing the butterflies in her lab. Altizer did, and it is those parasites—not necessarily the butterflies on which they live—that most interest her.

“I found that this disease occurred everywhere you could find monarch butterflies, but its prevalence varied strikingly in different geographic regions,” Altizer said. It was that finding, in part, that led her into her current experiment.

In her future work Altizer said she would like to take the results from her current monarch study and intersect them with her research into parasites. “I’d like to use some of the findings that come out of these general population divergence studies to conduct a separate set of experiments to go back and look at the interactions between the monarchs and their parasites and their possible coevolution,” Altizer said.

Checking for parasites does play a part in the current experiment. Cultures are taken from each butterfly, and if a parasite is found, the butterfly will be isolated from the others and the parasite investigated.

Altizer’s work is not exclusive to creatures lacking backbones. One of her projects is studying infectious diseases in wild birds. Right now she is looking at a bacteria that causes conjunctivitis, an eye affliction, in house finches.

Altizer also is one of several researchers around the country building a giant database categorizing parasites and infectious diseases around the world. The scientists have just finished cataloging parasites from primates and have begun coding hoofed mammals.

The versatility of this research is tremendous. “Do you tend to see more sexually transmitted diseases in promiscuous animals, for example,” Altizer said. “Or are there parasites that are transmitted by fecal/oral routes or by ingestion in animals which tend to be herbivores or grazers.”