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To survive the annual dry season, the fish's embryos enter a state of extreme suspended animation or "diapause" for approximately 8 months.

They report May 30 in the journal Cell that although killifish evolved diapause less than 18 million years ago, they did so by co-opting ancient genes that originated more than 473 million years ago.

Through comparative analysis, the team showed that similar specialized gene expression patterns are also employed by other animals -- including the house mouse -- during diapause.

"The whole program is like day and night -- there is life in the normal state and life in the diapause state, and the way this happened was by reshuffling or re-wiring the regulatory region of a whole set of genes," says senior author and molecular biologist Anne Brunet of Stanford University.

"It's roughly in the middle of development, and many organs are already formed by that stage -- they have a developing brain and a heart which stops beating in diapause and then starts again," says first author Param Priya Singh of the University of California, San Francisco.