Dolphin Study Provides Insight Into History, Conservation Of Species
October 30, 2013

Dolphin Study Provides Insight Into History, Conservation Of Species

April Flowers for - Your Universe Online

A research team from Nanjing Normal University and BGI has completed original genomic research on the Yangtze River dolphin (Lipotes vexillifer), commonly known as Baiji.

The study, published in Nature Communications, provides new insight into the genetic and evolutionary adaptations of dolphins and valuable resources for the conservation of mammals, and in particular, of cetaceans.

The baiji has been nicknamed "goddess of the Yangtze" and was regarded as a goddess of protection by local fishermen and boatmen in China. Largely due to the extreme pressures brought by human activity, the baiji has suffered huge losses in recent decades. Although the species has become one of the most famous in aquatic conservation, many of the efforts made to conserve the baiji have failed.

The research team presented a high-quality draft genome, as well as three re-sequenced genomes of the baiji using next-generation sequencing technology. The team compared the genomic analysis of baiji and the bottlenose dolphin, revealing that cetaceans have a slower molecular clock than previously thought.

Further analysis of the genome revealed that the genes involved in oxidoreductase activity, ferric iron binding, metabolic processes and ATPase activity show significant expansion. In contrast, the genes involved in olfactory receptor activity decreased most significantly. Researchers suggested that these changes in genes may be related with the baiji's basic physiological activities required for underwater living, such as oxygen-carrying and sensing.

Many factors were found that are related to the aquatic adaptations of cetaceans, such as positively selected genes (PSGs) and some functional changes. One finding never before reported in studies of mammals or dolphins is that the PSGs in the baiji lineage are also involved in DNA repair and response to DNA damage stimulus.

A classic example of convergent evolution is the independent origin of echolocation in toothed whales and bats. The research team investigated convergent evolution in the baiji and bat, finding nine genes - including SLC26A5, TMC1, and DFNB59 - that have evolved under significant accelerated evolution, and 17 genes that contained parallel amino acid changes in echolocating mammals.

The team found a significantly lower number of heterozygous single nucleotide polymorphisms (SNPs) in the baiji compared to all other mammalian genomes reported so far. By reconstructing the demographic history of the baiji, the researchers found that a bottleneck occurred near the end of the last deglaciation, a time coinciding with a rapid decrease in temperature and the rise of eustatic sea level.

Fengming Sun, project manager from BGI, said, "We not only found some special evolutionary characterics [sic] of baiji, but also found that the functionally extinct of this species was mainly due to human activities. The high-quality draft genome of baiji will provide a valuable resource for researchers to uncover the genetic mechanisms underlying extinct species, and will make a great contribution to the protection of endangered species."