A jellyfish-like hydrozoan with a novel power to rewind its life cycle has been spreading rapidly around the world’s oceans without anyone taking much notice, researchers say.

The life history of Turritopsis dohrnii takes such twists and turns that only a new genetic analysis has revealed that the creature is invading waters worldwide, says Maria Pia Miglietta of Pennsylvania State University in University Park.

The first peculiarity of the seven species of Turritopsis had inspired biologists to describe these hydrozoans as “potentially immortal.” The adults form filmy bells reminiscent of their jellyfish relatives. When times get tough, faced with scarce food or other catastrophe, Turritopsis often don’t die. They just get young again.

Normally the organisms reproduce like grown-ups with sperm and eggs. In case of emergency, though, a bedeviled bell sinks down and the blob of tissue sticks to a surface below. There Turritopsis’ cells seem to reverse their life stage. When the blob grows again, it becomes the stalklike polyp of its youth and matures into a free-floating bell all over again. “This is equivalent to a butterfly that goes back to a caterpillar,” Miglietta says.

That’s a fine trick for surviving the strains of being swallowed in a huge gulp of water for a ship’s ballast and being hauled around the world, Miglietta says. The creatures can restart their life cycles right in the bottom of the ballast tank. Ballast water has become the major route for moving alien species from one ocean to another, and that’s probably what’s happening to T. dohrnii, Miglietta said June 21 in Minneapolis during the Evolution 2008 meeting.

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The world’s most successful bacterial parasite has effectively become a part of at least 11 different animals by writing its entire genetic code into theirs, according to research that sheds important light on evolution.

Scientists have discovered copies of the genome of the Wolbachia bacterium lurking within the genetic code of fruit flies, wasps and nematode worms. So ingrained are the bacteria’s genes that they appear to have biological roles within the host animal.

The findings have important implications for evolution, as they show that genes can transfer from bacteria to unrelated multicellular organisms and take on new functions much more readily than was supposed previously.

This suggests that large-scale gene transfers may allow larger animals and plants to acquire new genes with beneficial effects extremely quickly, and then to pass them on to future generations. Such transfers are known to occur between bacteria and to have happened in the evolutionary past. Mitochondria, structures or organelles that provide cells with energy, are relics of bacteria that were absorbed by their host cells, as are the chloroplasts that allow photosynthesis in plants.

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