Researchers of Nanjing Normal University (NNU) have made important breakthroughs in the research of the Yangtze River porpoise. They found that the Yangtze River porpoise are genetically different enough to be considered a unique incipient species by sequencing and analyzing their genome and comparing it to 48 other finless porpoises from different regions.
The paper entitled “Population Genomics of Finless Porpoises Reveal an Incipient Cetacean Species Adapted to Freshwater” was published in the journal Nature Communications on April 10, 2018.
The findings were made by a research group led by Prof. Guang Yang of the School of Life Sciences and other researchers from the Harvard Medical School, University of California, Berkeley and the Beijing Genomics Institute (BGI).
NNU PhD candidate Di Sun，NNU Prof. Shixia Xu, Xuming Zhou, a PhD candidate of Harvard Medical School and Xuanmin Guang of BGI are the lead authors of this paper. Prof. Guang Yang, Prof. Rasmus Nielsen of University of California, Berkeley, and Dr. Xiaodong Fang of BGI are corresponding authors.
The research group led by Prof. Guang Yang reports the sequencing, de novo assembly and analysis of a finless porpoise genome, and the re-sequencing of an additional 48 finless porpoise individuals. They used these data to reconstruct the demographic history of finless porpoises from their origin to the occupation into the Yangtze River. Analyses of selection between marine and freshwater porpoises identify genes (ADCY1, DYNC2H1,SLC14A2, and ACE2) associated with renal water homeostasis and urea cycle, such as urea transporter 2 and angiotensin I-converting enzyme 2, which are likely adaptations associated with the difference in osmotic stress between ocean and rivers. The complete reproductive isolation of finless porpoises was also supported by a species delineation analysis using Bayes factors. The divergence of the Yangtze River population from other narrow-ridged individuals was influenced during the LGM (Last Glacial Maximum). Therefore, their results strongly suggest that the Yangtze finless porpoises are reproductively isolated from other porpoise populations and harbor unique genetic adaptations, supporting that they should be considered a unique incipient species.
The Yangtze finless porpoise is the only freshwater porpoise in the world. Unfortunately, there are only about 1000 Yangtze porpoises left. Each year, their population declines by about 14%. The main reasons for the Yangtze River dolphin decline seem to be the same as for the river dolphin: a combination of pollution and disturbances, habitat destruction, encounters with motorized boats, and fishing bycatches.
To prevent it from going the way of the Yangtze river dolphin, which was declared functionally extinct in 2006, measures need to be taken to ensure its food supply and safety. This study helps to emphasize the importance of enacting measures to protect the river porpoises including enforcing safe fishing practices, reducing pollution and enacting habitat reconstruction projects.”
Support for the project was provided by the National Science Foundation for Distinguished Young Scholars, the State Key Program of National Natural Science of China, and National Key Research and Development Program.