Male killifishCredit: Rogelio Barajas and Xiaoai Zhao
Scientists have finally explained how the African turquoise killifish has evolved to “press pause” on life to survive drought, allowing embryos to endure extreme environmental stress by halting their development until conditions improve.
In a study in Cell, they describe the genes involved and explain that although this ability, known as diapause, evolved quite recently, it relies on very ancient genes that were co-opted during evolution.
The African turquoise killifish live in seasonal ponds in Zimbabwe and Mozambique, and mature faster than any other vertebrate species. During diapause, the embryo’s heart stops beating, and all the developmental functions and division of cells stop for a long period.
“It is similar to pressing a pause button on life under harsh conditions without killing the organism, and reviving it later when the conditions improve,” says Param Priya Singh, the study’s co-author from the University of California, San Francisco in a press release.
While diapause is not unique to killifish, it can last much longer than in other animals — eight months on average and up to two years in the lab. And killifish embryos enter suspended animation much later in development.
“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 Singh.
The scientists analysed gene expression and used other genomic techniques in embryos of various killifish species to understand which genes are involved in regulating diapause, and how this capacity evolved.
They found similar specialised gene expression in the killifish and in other animals that have developed diapause, from other fish to the house mouse.
They conclude that diapause in the turquoise killifish evolved less than 18 million years ago by co-opting ancient genes that originated more than 473 million years ago.
