The geographical isolation of Africa and Eurasia allowed the independent emergence of fully aquatic mammals approximately 55 million years ago. While the molecular evolution of the more than 100 species of extant cetaceans has received considerable research attention, there has been less attention on the four species of extant sirenians: the dugong and three manatee species whose ancestors diverged ~30 million years ago. Here, I present recent research insights on the molecular evolution of sirenians. By juxtaposing genomes of the dugong and West Indian manatee, we revealed possible solutions to aquatic life by sirenians, including aquatic herbivory and daily activity patterns in shallow waters. Convergent loss of integumentary system genes, mainly those expressed in the outer layers of the skin, by sirenians and cetaceans agrees with the idea that convergent gene loss occurs in species with similar ecological pressures. We propose that sirenian loss of KCNK18 is related to their shift in activity patterns and may render sirenians, particularly manatees in the colder US waters, susceptible to the often-fatal cold stress syndrome (CSS). Finally, we show evidence that the plentiful Australian dugong populations are relatively healthy, but other populations worldwide may follow the Japanese and Chinese dugongs on the fast track toward extinction.
Genomic insights into the retransition to fully aquatic life within superorder Afrotheria