Genes lost during the transition from land to water in cetaceans highlight genomic changes associated with aquatic adaptations.

Abstract

The transition from land to water in whales and dolphins (cetaceans) was accompanied by remarkable adaptations. To reveal genomic changes that occurred during this transition, we screened for protein-coding genes that were inactivated in the ancestral cetacean lineage. We found 85 gene losses. Some of these were likely beneficial for cetaceans, for example, by reducing the risk of thrombus formation during diving (<i>F12</i> and <i>KLKB1</i>), erroneous DNA damage repair (<i>POLM</i>), and oxidative stress-induced lung inflammation (<i>MAP3K19</i>). Additional gene losses may reflect other diving-related adaptations, such as enhanced vasoconstriction during the diving response (mediated by <i>SLC6A18</i>) and altered pulmonary surfactant composition (<i>SEC14L3</i>), while loss of <i>SLC4A9</i> relates to a reduced need for saliva. Last, loss of melatonin synthesis and receptor genes (<i>AANAT</i>, <i>ASMT</i>, and <i>MTNR1A</i>/<i>B</i>) may have been a precondition for adopting unihemispheric sleep. Our findings suggest that some genes lost in ancestral cetaceans were likely involved in adapting to a fully aquatic lifestyle.