Earth’s weird and wonderful animal models

Credit: Sandy Kawano, Rick Blob

Consider, for a moment, the humble fruit fly. Genus Drosophila. Bulbous-eyed and papery-winged, this is the pest you’ve swatted away from fruit salad and cursed at in your kitchen.

In the scientific world, Drosophila is anything but humble; it is a model organism of powerhouse proportions. For over a century, scientists have used Drosophila to reveal insights about genetics and biological development. Multiple Nobel Prize-winning discoveries were founded on Drosophila research. Today, scientists are using the flies to better understand everything from the complexities of social behavior to sexual selection.

“Model organisms are vital for biological research,” says Robert Miller, a deputy division director in the National Science Foundation’s (NSF) Biological Sciences Directorate. “They allow us to explore fundamental biological processes; the rules of life universal to all organisms. We can then apply this knowledge to more and more complex species, such as humans.”

Fruit flies from a study on genetic variability. Credit: Dahlia Nielsen, NC State University

All model organisms share a few common traits: they’re inexpensive, easy to care for, grow quickly, and are relatively simple creatures. Drosophila isn’t the only with plenty of research to its name (or genus). There’s the mustard plant Arabidopsis,zebra fish, a particular strain of yeast.

Some researchers, however, are looking to more unique creatures to explore a new set of biological challenges, from how our earliest ancestors first walked on land to the chemistry of our nervous system.

“You can think of animals as the product of a long history of experiments in nature,” says Sandy Kawano, a postdoctoral researcher at the NSF-funded National Institute for Mathematical and Biological Synthesis (NIMBIoS). “There are lots and lots of things we can learn from them.” And when researchers step outside the traditional model organism box, they often seek new approaches and ask new questions. “So Earth’s diversity really does drive innovation.”

Our earliest steps

When Kawano wanted to study the movements of the first tetrapods — four-limbed vertebrates whose descendants include mammals — she turned to the tiger salamander. The earliest vertebrates are presumed to have moved from water to land about 400 million years ago; Kawano and her team at NIMBIoS and Clemson University wanted to know what factors drove changes in their bone function, as the animals became terrestrial. Tiger salamanders are a great stand in for the prehistoric creatures — they are not fossils, for one thing, and have a similar body plan and ecology to early tetrapods.

Kawano filmed the salamanders strolling across a device that recorded the forces exerted while walking, blended that with anatomical data and created a mathematical model to calculate limb strength. She found that salamander’s forelimbs were both stiffer and able to withstand higher loads, meaning the bones in the front legs were stronger.

The study offers new insights into how form drives function in animal limbs, and sheds light on both the fossil record and prehistoric life on Earth.

Songs of the city

A white-crowned sparrow. Credit: Sebastian Kennerknecht

David Luther is studying a slightly more modern phenomenon: how animals adapt to urban environments. With NSF funding, the George Mason University biologist is using white-crowned sparrows to explore the ways cities, and particularly the human noise within, change how birds communicate.

White-crowned sparrows are a particularly good species for such study. The bird is almost like the Drosophila of animal acoustics; different subspecies have distinctly different songs, making it ripe for research on animal communication.

“We want to know how and why animals are changing the way they communicate acoustically,” Luther says. “Are they learning their songs? Is it a fixed sort of thing or is it a more plastic behavior?”

Credit: Sebastian Kennerknecht

Luther and his collaborator, Elizabeth Derryberry of Tulane University, compared white-crowned sparrow song recordings from the 1960s to songs from today. They found that the birds have changed the pitch of their song, likely to be heard over rush hour traffic. The birds also sing louder, just the way you’d raise your voice when walking by a bustling construction site.

They still don’t know exactly the consequences of this adaptation, and how it affects the signals embedded in bird song (often akin to “Ladies! I’m over here!”). They have found that male birds singing at louder sites — and therefore adjusting their pitch — sing songs with lower vocal performance, meaning they are less competitive for mates.

The study could have larger implications for how species exist in urban settings.

“Most animals, whether it’s a bird or something else, when they’re presented with a lot of loud noise they just leave,” Luther says. “But there are some animals that persist. If we find out how and why they’re able to persist, we could apply this to other species as well.”

Weaving a web

A European garden spider. Credit: Wilder Kaiser

The squat European garden spider relies on vibrations to communicate; its own song, of sorts, played on the spider’s web. This kind of communication may be alien to humans, but vibrations are “one of the most common ways animals sense the world,” says Damian Elias, a biologist and associate professor at University of California Berkeley.

“By understanding it, we’re really opening a window into how different life on Earth functions.”

With NSF funding, Elias has teamed up with Ross Hatton, an Oregon State University engineer, to probe the physics of spider web vibrations.

European garden spiders, common throughout Europe and North America, weave orb-style webs. It serves as their entire sensory world. Webs are complicated yet delicate structures, and the spider uses it to distinguish between prey and predator, mate and foe.

Hatton has engineered a larger-than-life artificial spider web in his lab. The web is made of two materials — nylon and elastic latex cords — mimicking the two kinds of thread spiders use to build their webs. It’s set in a sort of subwoofer frame; the speakers cause the web to vibrate in different ways, the way real webs do. The “spiders” are eight-legged frames with accelerometers at each leg, allowing Hatton to measure web vibrations at a fine scale.

Credit: Andrew Otto, Oregon State University

Hatton’s experiments feed into a computational model which Elias tests in his lab, with actual European garden spider webs. It’s a fundamental physics question — how do strings that are bound together move — with a real-world, eight-legged counterpart.

“It’s tapping deep into all sorts of engineering and physics problems, to really understand what’s happening in the spider’s world,” Hatton says.

That understanding could extend to other spiders, shedding light on the behavior and ecology of one of Earth’s most numerous animal groups.

Spider webs, like other biological structures, are also pretty miraculous feats of engineering. They must be strong enough to withstand destructive impacts from predators, inviting enough to snag prey and flexible enough to survive in an elastic environment.

This research could lead to biological inspiration for new materials or structures, Elias said. “That’s one of the nice things about basic research. The sky’s the limit.”

Hungry for more animal model stories? Look no further than the field of neuroscience — understanding the human brain requires studying squishy, strange organisms of all shapes and sizes.

In the video above, scientists use African clawed frogs to learn how neural circuits develop and absorb information from the surrounding environment. Recordings from echolocating bat brains have given researchers a view into how mammals understand 3-D space.

Credit: Z Yan Wang, Ragsdale Lab, University of Chicago

The octopus genome sets the stage for future studies on complex nervous system development. Roundworms help us research the parallel development of brain circuits and behavior.

And of course, Drosophila has something to teach us, too.

“That’s one of the nice things about basic research. The sky’s the limit.”