The scientist --life inspiring innovation muscle bound

09.2018 | THE SCIENTIST 25

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carbon isotopes in the environment. And

then there’s the matter of those missing

birds—killed off by people and the rats

and other animals they brought with

them—and the absence of their nitro-

gen-filled poop. “The islands lose a key

nutrient input in the seabird guano,”

Swift says, although she adds that that’s

just one of many factors that can change

island landscapes’ nutrient composition.

On Agakauitai, she and her coauthors

suggest, the shift toward carbon-13 indi-

cates that people—and the rats that ate

their scraps—favored a fish-rich diet, while

the opposite trend on some other islands is

consistent with an increasing reliance on

the C3-photosynthesizing crops, such as

taro, that Polynesians tended to cultivate.

Although the isotopes in their bones

may not tell a complete story, rats are

unique archaeological resources in a few

ways, says molecular anthropologist Lisa

Matisoo-Smith of the University of Otago

in New Zealand who was not involved in

the new study. For example, unlike Homo

sapiens settlers, rats have maintained a

constant presence on the islands. “Even

when humans may have abandoned entire

islands or parts of islands or sites, the rats

are still going to be there,” she tells The

Scientist. Analyzing isotopes and changes

in diet in rat remains is “a brilliant idea

... and to see it applied through time
and across space in the Pacific gives us
some really valuable insight”—into both
the changes wrought by humans’ arrival
and into the changing activities of those
humans over time.
Swift, a.k.a. @DrRatGirl on Twitter,
plans to continue mining the bones of
rats and other animals that live around
humans for more of this insight. “Com-
mensal animals in general are a really
under-researched and interesting topic,”

she says. “There’s a lot they can tell us

about people and environments.”

—Shawna Williams

Silent Swimmer

A flattened, almost completely transpar-

ent object moves slowly through the water.

In its appearance, the colorless structure

somewhat resembles an eel larva—and

for good reason: this marine robot was

designed with a leptocephalus, the name

of a curious stage in the lifecycle of several

eel species, in mind.

“We want to make a soft robot that can

swim around coral reefs without damaging

them,” says Caleb Christianson, a doctoral

student at the University of California, San

Diego (UCSD), who has been working on a

prototype for more than a year and a half.

Marine robots have various uses. The

oil and gas industries use unmanned vehi-

cles for tasks such as installing under-

Rats bones are a unique

archaeological resource.

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