“For me, this was the moment on the road to Damascus,” entomologist James Truman told me, recalling an encounter when he was sixteen. “My family has a summer retreat on Lake Erie, a trailer. As I was walking through the trailer park, I looked up and saw an insect in a tree. It was a parasitic wasp with a three-inch abdomen.” He thought, What exactly is this? That curiosity, Truman said, “made me buy a book.” This is Frank E. Lutz’s Insect Field Manual, first published in 1918, with detailed drawings by scientific illustrator Edna Libby Beutemüller. “I always knew I wanted to be a biologist, but I’d moved from one interest to another: birds, mammals, whatever,” Truman said. Then he changed. He knew he would study insects.
Insects are indeed small, but they represent more than eighty percent of all animal species. They also have a special magic: most undergo complete metamorphosis. A ladybug begins as a spiny black crawler. The garden tiger moth begins as a hairy caterpillar. Some fish and amphibians also metamorphose (mammals don’t!), but since insects have exoskeletons – their metamorphosis happens out of sight – the effect could be Athena-like when the adult organism is fully formed As amazing as turning a fallen sandpiper into a partridge, or Daphne into a laurel tree.
As a freshman at Notre Dame, Truman worked in the mosquito genetics laboratory run by renowned entomologist George Craig, spending time with his arms on mesh cartons full of mosquitoes that would feed—suck His blood – when he ate his lunch. When Truman arrived, Craig’s lab was primarily focused on identifying mutations that might help improve mosquito-borne diseases, along with a side project studying a pheromone called materone. During mating, male mosquitoes release estrogen, which makes female mosquitoes less willing to mate. “She just wanted blood,” Truman said. Therefore, female mosquitoes mate only once. “It was amazing to me,” Truman noted, “that one hormone could cause such a dramatic change in behavior.”
Truman did his graduate work in the laboratory of Harvard biologist Lynn Riddford. She is also interested in hormones and other factors that affect insect growth and behavior. (The two later married, though Riddford told Truman she would not marry him until he graduated.) This inquiry continued to inform Truman’s research. “I’m working on a giant silk moth,” Truman said, a creature whose life cycle is as varied as any Ovidian story’s shape-shifting. At first, it is a tiny caterpillar, about six to seven millimeters long. It then molts four times, during which time it grows to nearly a thousand times its original size, wraps itself in a silk cocoon, and becomes a large moth without a functional mouth, unable to eat, and thus dies in less than seven days. Will die has passed, so plan to mate immediately. Truman studied the hormones that regulate these transformations and was “fascinated by metamorphosis and interested in its behavior,” he said. “Those interests came together to understand exactly how the brain changes during metamorphosis. I wanted to understand how the caterpillar brain becomes the moth brain.”
During a sabbatical at Cambridge, Truman and Riddifford took a break from moth research to study Drosophila, commonly known as Drosophila. “These giant silk moths don’t have genetic tools, but they have good genetic tools Drosophila,” Truman said. Scientists have a very detailed understanding of the genetic makeup of fruit flies. Tools exist to knock out specific genes and change how or when the genes express themselves. You can easily order fruit flies with various mutations, and even Fruit flies can be ordered with a genetic mutation that causes them to grow legs where their antennae would normally grow. Such research dates back nearly a century to the work of biologist Thomas Hunter Morgan work at Columbia University, where he directed the “Flight Room.” Today, researchers have access to more than 2 million rows Drosophila; this allows you to precisely manipulate virtually any aspect of biology at the larval or adult stage. Truman said: “With fruit flies, we are only limited by our imagination and not limited by our technology.”
Truman and his team wanted to understand the fine anatomical details of how much of the larval brain was retained in the adult fly’s brain. “We can imagine a little grasshopper, and what it’s upbringing might affect how its brain works, because they don’t go through complete metamorphosis,” Truman said, using the grasshopper as an example. “But when an insect undergoes such a drastic change,” How about a complete metamorphosis? “So do you come across as a blank slate? Or is your adult life somehow skewed by a larval life?” in a paper recently published in the journal electronic lifeTruman’s team traced neural connections between Drosophila From larva to adult – what is reshaped, what is destroyed, what is regenerated.
Truman’s team studied the nerve center of the larval brain, the mushroom body, which regulates olfactory learning. For insects, smell is by far the most important sense. Larvae may learn to associate a certain smell with something positive or negative. But do adult flies remember the connections they formed when they were young? We can think of this as Pavlov’s fruit fly problem. What Truman’s team did was find a way, in anatomical detail, to see if these neuronal connections remained stable through metamorphosis, “to see if there was any continuity,” Truman said. “No.” I mean, the brain is a complicated place. But at the simplest level, these neuronal relationships are disrupted, they disappear. “
We often think of our “self” as being located in our brains. Truman’s piece reminds me of a classic question: If every plank and part is replaced, does the Ship of Theseus remain the same? It is a kind of identity case for deformed arthropods. “It’s the ultimate ‘me, myself, me’ situation,” says Bertram Gerber, chair of the Department of Learning and Memory Genetics at the Leibniz Institute of Neurobiology. Gerber described Truman’s work as “the most in-depth look to date at what happens in the brain during metamorphosis,” noting that it showed “with unprecedented detail, precision, and experimental elegance” what’s going on in insect brains. How the connections are pruned and regenerated so dramatically.
Despite the fact that we slap and trample them – if we don’t want to ignore them – the total biomass of insects is greater than that of humans. They are not always so dominant. In the early Carboniferous period (about 375 million years ago), when there were meter-long scorpions and six-meter-long crocodile-like creatures, insects somehow grew wings. “For about 50 million years, no one else was able to fly — insects had their own air,” Truman said. However, fossils show that young insects had small wings that were easily damaged. One evolutionary solution is to allow wings to develop within protected wing pads. Wings emerged when the insect became an adult, a growth pattern we see today in insects such as grasshoppers and cicadas. It’s a change—a metamorphosis—but it’s called “incomplete.” It’s not as dramatic as the classic example of a caterpillar turning into a butterfly, a change so intuitively implausible that a naturalist was arrested in Chile in the nineteenth century for leaving a caterpillar to a girl and told her that if she fed them they would turn into butterflies; the townspeople in power considered this heresy.
Tens of millions of years after the development of wings, a complete metamorphosis occurred. “Things happened,” says Truman, “and then there was an explosion in the diversity and number of insects.” Ants, bees, flies, mosquitoes, moths—these highly successful orders all underwent complete metamorphosis and shared a common ancestors.
The practical benefits of metamorphosis are not immediately clear to non-biologists. The deformation appears too grand and complex. What reward is there for changing one’s body so drastically that it’s worth the effort? Truman recalls: “My former mentor, Carol Williams, used to say, ‘The caterpillar is the gut that goes on the caterpillar’s tracks and then becomes a flying machine dedicated to sex.'” Metamorphosis allows for extreme specialization : Feeds and grows in the larval stage, then mates in the adult stage. “If you look at an example of incomplete metamorphosis, like a grasshopper, the baby grasshopper and the adult grasshopper eat the same thing, so they’re competing for resources,” Truman said. “Suddenly, by metamorphosis, you can separate resources.” The caterpillar would Eat leaves; butterflies will feed on nectar. What’s more, the short-lived larvae can adapt to eating short-lived food sources, like fruit flies on rotting orange halves, or dung beetles on deer droppings.
What stood out as part of the work Truman and Riddiford had done over the years was their well-supported conjecture that, in insects with complete metamorphosis, the early stages of the animal evolved later than the adult forms. When we see a tadpole (a fish-like thing) grow into a frog (a creature that can live on land), it’s the opposite, somewhat flawed, but enlightening view of evolution we get. The life cycle of the frog is like a repeat of the evolution of fish into amphibians over eons. For insect metamorphosis, the timeline can be said to run backwards, with the most recent development, larvae emerge first, and then, as if time was reversed, become traditional adults. Young people are crazy inventions.
When German botanist and entomologist Maria Sibylla Merian was thirteen, she owned a cardboard house where she raised silkworms and watched them cocoon. Born in 1647, a year before the Treaty of Westphalia that ended the Thirty Years’ War, Merian was apprenticed to her stepfather, a painter. As an artist, she depicts the life cycles of silkworms, caterpillars, and other ever-changing creatures, and her work is known for showing the environments and food sources of these creatures as she can see them in their fields. She later left her husband and joined a religious commune for three years before, after her mother died, she took her two daughters to Amsterdam to support herself by running a painting studio and selling prints and unusual plants and insects Own. At fifty-two, she traveled to Suriname with her daughters, where she stayed for about two years, documenting miracles that others suspected, such as tarantulas big enough to eat hummingbirds and ants using their bodies as shelters for other ants. bridge. cross. Enslaved people help Merian in Suriname find flora and fauna.
Merian may also be the first to document the life cycle of the parasitic wasp that caught Truman’s attention when he was a teenager. She described some of the cocoons she was expecting butterflies to emerge from, only to find wasps instead. Darwin also observed parasitic wasps, and speaking of them, he could not convince himself that “a merciful and almighty God would have purposely” created them. ❖
