Getting a grip on the slow but unique evolution of sharks

Date:  October 8, 2018

Scientists at the RIKEN Center for Biosystems Dynamics Research (BDR) in Japan, in collaboration with other Japanese institutes and aquariums, have decoded the whole genomes of two shark species for the first time and improved the whale shark genome sequences released previously. By analyzing the genomes and comparing them with those of other vertebrate species, they have constructed an overview of their unique life histories and evolutionary paths. This work was published online in Nature Ecology and Evolution.

Advances in genome sequencing have made it possible to compare genomes from different species, giving us insights into their evolutionary histories and characteristics. While data for many organisms are available, to date, genome sequencing for sharks has been hampered by their huge genomes, which are even larger than the human genome. The notable exception is the elephant shark, although strictly speaking this fish is not professionally classified as a true shark.

Sharks have many unique characteristics, including their body structures, reproductive systems, way of sensing, and extreme longevity -- a shark species is known to live for more than three centuries. Fully decoded shark genomes will be a tremendous help to research aimed at discovering the molecular bases for these qualities. With this ultimate goal in mind, a research team led by Shigehiro Kuraku at RIKEN BDR analyzed shark genomes using cutting-edge DNA sequencing technologies and comparative bioinformatics that were able to deal with gigabase-scale sequences. They chose two primary species -- the brownbanded bamboo shark and the cloudy catshark -- because they can be raised in aquariums, making it relatively easy to constantly obtain live specimen. They also performed an improved assembly of the whale shark genome, which had been previously released.

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