An Experiment Repeated 600 Times Finds Hints to Evolution's Secrets
In a lab in Atlanta, thousands of yeast cells fight for their lives every day. The ones that live another day grow fastest, reproduce quickest and form the biggest clumps. For about a decade, the cells have evolved to hang onto one another, forming branching snowflake shapes.
These snowflakes are at the heart of experiments exploring what might have happened when single-celled creatures first banded together to become multicellular. That process, however it went down, eventually resulted in fabulously weird organisms like octopuses and ostriches and humans.
Although multicellularity is thought to have evolved at least 20 times in the history of life on Earth, it is far from obvious how living things go from a single cell to many that share a fate. But, in a new paper, researchers reveal one clue to how cells could start building themselves into a body. The team that produced the snowflake yeast found that over 3,000 generations, the yeast clumps grew so large that they could be seen with the naked eye.
Will Ratcliff, a professor at Georgia Tech, began the yeast experiments when he was in graduate school. He was inspired by Richard Lenski, a biologist at Michigan State University, and his colleagues who have grown 12 vials of E. coli through more than 75,000 generations, documenting since 1988 how the populations have changed. Ratcliff wondered if an evolution study encouraging cells to stick together could shed light on the origins of multicellularity.
So he set up a simple experiment. Every day, he swirled yeast cells in a test tube, sucked up the ones that sank to the bottom quickest, then used them to grow the next day's population of yeast. He reasoned that if he selected for the heaviest individuals or clumps of cells, there would be an incentive for the yeast to evolve a way to stick together.
And it worked: Within 60 days, the snowflake yeast appeared. When these yeast divide, thanks to a mutation, they don't fully separate from one another. Instead they form branching structures of genetically identical cells. The yeast had become multicellular.
-- VERONIQUE GREENWOOD
Why Are Insects Drawn to Light? A Perennial Question Gets a New Answer
Insects are drawn to lights at night as reliably as planets orbit stars. Entomologists have exploited this by setting out light traps to collect insects, and poets have used the image of a moth drawn to flame to signify self-destructive behavior. Ecologists worry the lure of artificial lights may help explain why insects are in global decline. But it's still unclear why insects find light so appealing.
The Harvard biologist Avalon Owen said that one prevailing theory, popular but flawed, was that insects confused porch lights for the moon or another celestial body, scrambling their sense of navigation. Another idea is that night lights look like glimpses of daylight through a thicket of vegetation, prompting insects to try to make a beeline toward what they think is open space.
Now there is a new possible answer. A team led by Samuel Fabian at Imperial College London and Yash Sondhi at Florida International University say that when insects see a light at night, they believe they've found the sky's direction and try to orient themselves along an up-and-down axis. That prompts them to roll their backs toward the light, mistakenly in cases when the illumination is on the ground, causing them to go into endless turns like a tiny airplane or to crash-land.
-- JOSHUA SOKOL
Fruitarian Frogs May Be Doing Flowers a Favor
On warm evenings near Rio de Janeiro, you might find milk fruit trees covered in brownish-orange frogs. While many frogs eat insects, the tree frog species Xenohyla truncata has a taste for the pulp of bulbous fruits and the nectar in the tree's flowers.
As they seek that nectar, the frogs dunk their entire bodies into the plant's flowers, only their butts sticking out. When they emerge, pollen gets stuck to their heads and backs. Then they hop off, potentially transporting the pollen from their previous stop at the tropical buffet into the next milk fruit flower they encounter.
In other words, the frogs may disperse the plant's seeds and pollinate its flowers -- which would be the first time this has been seen in an amphibian.
"That's completely, completely new, till now, nobody saw them actually doing that," said Luís Felipe Toledo, head of the Amphibians Natural History Lab at the University of Campinas in Brazil and an author of a study suggesting the existence of this ecological relationship between frog and flowering tree.
"This is a very exciting and intriguing first observation," said Ruth Cozien, an expert on plant-animal interactions at the University of KwaZulu-Natal in South Africa who was not involved in the study. She said more observations were needed to confirm pollination, but called the early evidence "incredible."
-- SOFIA QUAGLIA
How Deep-Diving Sharks Stay Warm Will Take Your Breath Away
Hammerhead sharks like it warm, but for a good meal they're willing to get cold. The flat-headed predators dive more than 2,600 feet from tropical surface waters into the ocean's frigid depths multiple times every night to hunt for fish and squid, tolerating a 68-degree Fahrenheit plunge in temperature to dine.
How do these coldblooded chondrichthyans tolerate these temperatures without turning into frozen fish? A new study shows how one species -- Sphyrna lewini, or scalloped hammerhead sharks -- stay warm during their nightly dives: They skip the frills and close their gills, essentially holding their breath.
This strategy for regulating a coldblooded fish's temperature has never been observed before and distinguishes them from high-performance fish (yes, that's the scientific term) like great white sharks or Atlantic bluefin tuna that use vastly different strategies to tolerate extreme cold.
Mark Royer, a shark biologist in Hawaii, was inspired to investigate the scalloped hammerhead's secret heating technique after noticing how deep they were diving. He attached a package of sensors near the dorsal fins of six hammerheads near Hawaii.
He and his team found that the hammerheads lose a little body heat when they start their descent, but then quickly return to the same temperatures they were at the surface as they swim deeper. Even when the surrounding water was as cold as 39 degrees Fahrenheit, the sharks had body temperatures around 75 degrees during hourlong dives.
-- DARREN INCORVAIA