Genetics: The genome of a fish-out-of-wate

The genome of the mudskipper, an amphibious fish that uses its pectoral fins to move around on land, is revealed in Nature Communications this week. Mudskippers have evolved a suite of adaptations to help them cope with terrestrial life. These include the ability to breathe, see well and move around on land, and also the ability to tolerate high levels of environmental ammonia.

Qiong Shi and colleagues sequenced the genomes of four different species of mudskipper. Their results show that mudskippers diverged from other ray-finned fish around 140 million years ago and went on to acquire hundreds of genes that helped them to live on land. Several genes of the ammonia excretion pathway have undergone positive selection suggesting a role for them in ammonia tolerance, while an enlarged collection of innate immune system genes likely helps protect the fish against land-living pathogens. Certain vision-related genes have become lost or mutated, while the gene expression profiles of mudskippers exposed to air have helped to highlight molecular pathways that may help the mudskipper cope with low oxygen environments.

The work highlights genes and molecular mechanisms that may have helped mudskippers to adapt to their unusual lifestyle and that may also have helped other, more ancient vertebrates make the transition from water to land some 360 million years ago.