Molecular Mechanisms of Reduced Risk of Decompression Sickness in Deep Diving Cetaceans

Abstract

Background Cetaceans, having experienced prolonged adaptation to aquatic environments, have undergone evolutionary changes in their respiratory systems. This process of evolution has resulted in the emergence of distinctive phenotypic traits, notably the abundance of elastic fibers in their lungs. These fibers facilitate the collapse of cetaceans' lungs during dives and subsequent re-expansion upon surfacing, effectively reducing the risk of decompression sickness. Such adaptations play a crucial role in minimizing the risk of decompression sickness during deep dives. Nevertheless, the scientific inquiry into the mechanisms through which these unique phenotypic characteristics govern the diving behavior of marine mammals, including cetaceans, remains unresolved.Results This study entails an evolutionary analysis of 42 genes associated with pulmonary fibrosis across 45 mammalian species. Twenty-one genes in cetaceans exhibited accelerated evolution, featuring specific amino acid substitutions in 14 of them. Primarily linked to the development of the respiratory system and lung morphological construction, these genes play a crucial role. Moreover, among marine mammals, we identified eight genes undergoing positive selection, and the evolutionary rates of three genes significantly correlated with diving depth. Specifically, the SFTPC gene exhibited convergent amino acid substitutions. Through in vitro cellular experiments, we illustrated that convergent amino acid site mutations in SFTPC contribute positively to pulmonary fibrosis in marine mammals, thereby reducing the risk of decompression sickness during diving.Conclusions The study unveils pivotal genetic signals in cetaceans and other marine mammals, arising through evolution. These discoveries yield substantial biological insights into how these species mitigate the risk of decompression sickness during dives. Moreover, the research serves as a valuable reference for delving deeper into human diving physiology.