SYNTHETIC BIOLOGY. Synthetic microbe has fewest genes, but many mysteries.
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sciencemag.org SCIENCE IM A G E : M A R K E L L IS M A N / N A T IO N A L C E N T E R F O R I M A G IN G A N D M IC R O S C O P Y R E S E A R C H olooza capture the creatures as they ingest tiny crustaceans and zebrafi sh genetically engineered to glow red with fl uorescent protein. Because comb jellies are translucent, the prey can be seen as it circulates through a network of canals lacing the jellies’ bodies. Fast-forward, and 2 to 3 hours later, indigestible particles exit through the pores on the rear end. Browne also presented a close-up image of the pores, highlighting a ring of muscles surrounding each one. “This is a sphincterlike hole,” he told the audience. “Looks like I’ve been wrong for 30 years,” said George Matsumoto, a marine biologist at Monterey Bay Aquarium Research Institute in Moss Landing, California, after he saw Browne’s talk. “If people don’t see this video, they won’t believe it,” he added. Matsumoto said he, as well as the biologists before him, likely missed the bowel movements because they did not observe their animals long enough after a meal. Jellies seen to expel waste from their mouths might have been, in ef ect, vomiting because they were fed too much, or the wrong thing. According to recent DNA analyses, comb jellies evolved earlier than other animals considered to have one hole, including sea anemones, jellyfi sh, and possibly sea sponges. (Some studies suggest sponges arose fi rst.) Consequently, Browne’s as-yet unpublished fi ndings disrupt the step-wise progression of digestive anatomy from one to two holes early in animal evolution. One possibility is that the comb jellies evolved through-guts and anuslike pores on their own, independent of all other animals, over hundreds of millions of years. Alternatively, a through-gut and exit hole may have evolved once in an ancient animal ancestor, and subsequently became lost in anemones, jellyfi sh, and sponges. Perhaps if you’re an anemone or a sponge stuck to a rock, suggests Matsumoto, it’s better to push waste back into the current rather than below. Browne is currently exploring the latter theory by seeing whether comb jellies activate the same genes when developing their pores that other animals do when growing an anus. If he fi nds that the genes are different, the evolution of our most unspeakable body part will no longer be considered the singular event zoologists long supposed. “We have all these traditional notions of a ladderlike view of evolution, and it keeps getting shaken,” says Kevin Kocot, an evolutionary biologist at the University of Alabama, Tuscaloosa. j