Genetics: How the Yangtze finless porpoise adapted to freshwater

Genes that may explain how finless porpoises came to inhabit the Yangtze river are described this week in Nature Communications. Unlike their ocean-dwelling relatives, the critically endangered Yangtze porpoises are adapted to freshwater and harbour genetic variants that could account for changes in kidney function and maintain the right balance of water and salts in the blood.

Based on genomic data collected from 49 finless porpoises in East Asia, Rasmus Nielsen and colleagues show that the Yangtze finless porpoises differ from other populations at the genetic level, suggesting they rarely breed with other varieties and may represent an incipient species. Variants of genes encoding proteins related to kidney function - one that transports urea and another that regulates the amount of sodium reabsorbed to the bloodstream - show signatures of Darwinian selection among Yangtze porpoises suggesting they may be advantageous for a freshwater lifestyle. This could reflect a need to conserve salt; essential for river porpoises but unproblematic for their marine counterparts.

The finless porpoises are the last remaining cetacean in the Yangtze following the recent extinction of the Yangtze river dolphin. The authors hope that the genetic data, illustrating the distinctive genetic makeup of the Yangtze population, will spur ongoing efforts to prevent habitat destruction.