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Genomics

Crawly critters’ mysteries and marvels

by Tien M. Nguyen
June 11, 2018 | APPEARED IN VOLUME 96, ISSUE 24

 

Green-blooded mystery

New Guinea lizards taste kind of like bad sushi, according to biologist and apparently adventurous diner Christopher C. Austin.

Louisiana State University’s Austin was a graduate student when he snacked on the raw lizards—one with red blood and one with exotic green blood—to test a hypothesis. Perhaps green-blooded lizards tasted worse to predators than red-blooded ones, giving them an evolutionary edge that might explain how some lizard species got green.

The peculiar color, which paints the lizards’ bones, tongues, and tissues lime green, comes from the bile pigment biliverdin. Too much biliverdin in blood leads to illnesses such as jaundice in humans and other vertebrates, yet the green-blooded lizards can stand shockingly high levels of the bile.

As for the edible experiment, Austin found that both types of lizards tasted about the same: “not horrible.” His hypothesis was ultimately “squashed” when later experiments showed that the lizards’ natural predators, such as snakes and birds, ate green and red-blooded lizards with equal abandon.

But Austin, ever the hardy herpetologist, was undeterred. Almost three decades later, he and his team unveiled an evolutionary map that traced green-blooded New Guinea lizards back to a single red-blooded ancestor. They found that six green-blooded lizard species, which included two new species, originated on four distinct branches of the tree (Sci. Adv. 2018, DOI: 10.1126/sciadv.aao5017).

The researchers constructed the evolutionary tree by sequencing DNA from a large number of lizards, which Austin collected over 14 expeditions to New Guinea, each time adding the lizards to the repository at LSU’s Museum of Natural Science, where he’s the head curator of amphibians and reptiles.

But even though the scientists are able to pinpoint where green-blooded lizards’ lineage branched off, they still don’t know why it happened. One hypothesis is that the green blood may be less hospitable to malaria parasites.

The mystery of why some lizards have green blood remains, but so too does Austin’s determination to solve it. And his scientific curiosity, as he’s shown, is insatiable.

 

Learning to leap, spider-style

Credit: Girupakaran Sivalingam, Bill Crowther and Mostafa Nabawy
Mad ups: Kim conquered every jumping task that came her way.

Biologists aren’t the only ones fascinated by crawly creatures. For example, arthropods, or “natural robots,” as Mostafa Nabawy calls them, are inspiring to aerospace engineers like him who hope to learn from their remarkable movements.

Nabawy’s team at the University of Manchester was interested specifically in jumping spiders. Unlike bugs that jump to escape their predators, spiders, who prey on these insects, jump differently: They favor speed and accuracy, not distance.

Jumping spiders’ desire to jump, however, can be hard to predict. For weeks, the team attempted to train four spiders to leap from one platform to another by repeatedly placing them on the jumping platform and then the nearby landing platform. Only one spider, nicknamed Kim, deigned to jump. “Once she got it, she got it,” he says.

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Kim performed 15 jumping tasks, which included vertical heights up to two body lengths and distances up to five body lengths (Sci. Rep. 2018, DOI: 10.1038/s41598-018-25227-9). The researchers observed that Kim, who was very smart, Nabawy says, was able to adjust her trajectory angle at launch depending on the difficulty of the task. For far or high jumps, she sprang at steeper angles, minimizing the energy required, while for short and level jumps, she adopted shallow angles to maximize her speed.

The team calculated the energy costs of the jumps and suggested it was possible that Kim propelled herself using muscles instead of through a hydraulic mechanism, which has long been debated by the field.

Kim, sadly, escaped her earthly bonds and leapt to that big spiderweb in the sky (jumping spiders usually live about a year), but her athletic contributions to science live on.

Tien Nguyen wrote this week’s column. Please send comments and suggestions to newscripts@acs.org.

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