Evolution: animal, vegetable or both? (Evolution)

by David Turell @, Tuesday, February 05, 2019, 17:46 (351 days ago) @ dhw

Exactly what has been found in planktons:


"After some groundbreaking experiments, Stoecker was one of the first scientists to describe how these types of plankton not only hunted their prey, but also sequestered the chloroplasts of their food sources and used them to get energy from sunlight. “I was very excited to find that they really were photosynthetic,” she says.

"Traditionally, marine microplankton had been divided similarly to species on land. You had plant-like phytoplankton, such as algae, and animal-like zooplankton that ate the phytoplankton. What Stoecker found was that some of these organisms were somewhere in the middle: They could eat like animals when food was present and photosynthesize like plants in the light. “If you think about it, it can be the best of both worlds,” says marine ecologist Dave A. Caron of the University of Southern California.

"Today, there’s growing realization that these in-between beasties — dubbed mixotrophs — are not only widespread but also play vital roles in the ecology of the oceans.

"At first, mixotrophs were considered a rarity of nature and no more than an evolutionary curiosity, but it soon became clear that they were widespread and abundant. In her first samples, Stoecker reported that more than a third of ciliates had chlorophyll in them. With time, more and more planktonic species that were previously considered either phytoplankton or zooplankton came to be recognized as mixotrophs.

"Scientists know now that there are myriad mixotrophs in the ocean and they come in all kinds of shapes and sizes, as well as in two main types. There are constitutive mixotrophs, whose own physiology permits production of energy from the sunlight. And there are non-constitutive mixotrophs, like Stoecker’s Strombidium and L. strobila, that must steal photosynthetic organelles from their prey, or keep whole algae hostage within them, in order to do it.

"It took a long time for anyone but plankton biologists to be especially interested in mixotrophs, says Stoecker, now at the University of Maryland’s Center for Environmental Science. But in the last decade, as evidence of their abundance and diversity builds up, their pivotal role in the marine ecosystem has become clearer.


"In a free-for-all frenzy, mixotrophs eat algae, animal-like plankton and each other, and are placed in the lower, broad base of food-web pyramids. The importance of their role in the ocean came to light when scientists started including mixotrophy in food web models — simulations of how the food web works under different conditions. What they found is that the survival of bigger organisms depends heavily on mixotrophs.

“'It’s basically redefining marine ecology,” says Mitra. “The base of the food web has practically changed.”


"As much as we know about mixotrophs now, “there’s still a big unknown,” says Stoecker. “In the ocean, in general, we still don’t know how many mixotrophs there are and how active they are.” Researchers are now studying the role mixotrophs play in Arctic regions and in other oceanic conditions.

"Scientists are also working on developing new methods to study the creatures’ physiology. But perhaps the biggest task has been reanalyzing species of plankton to check for mixotrophy since, historically, scientists would only classify plankton as plant-like or animal-like. “We were only studying half of it,” says Mitra. “We had to go back and reclassify the whole protist kingdom.” Advances in DNA sequencing technologies are making this endeavor easier, while also resolving the distribution and location of mixotrophs in the global oceans.

Comment: The bush of life gets bushier. This is no surprise. Photosynthesis appears in many forms.

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