Marine terpenoids and the conquest of land

Many sessile or slow-moving marine organisms, especially cnidarians, sponges, and opisthobranch mollusks, have a strong smell, but only if they are taken out of the water, because their water-insoluble molecules are volatile in air. Like their terrestrial volatile counterparts, the marine liposoluble metabolites play important roles in chemical communication, mediating key biological processes in the aquatic environment, such as sexual reproduction, nutrition, and defense. In spite of this, the notion that chemical communication in aquatic environments is mediated only by hydrophilic compounds, while odorants on land, needing to be volatile, are hydrophobic, is overemphasized in a number of research papers. Contradictory speculations on the evolution of olfactory receptor genes do not help to shed light on the issue. These incongruities call the field of chemoreception to reassess its paradigmatic foundations and the empirical and theoretical work conducted within them. Based on our most recent findings on the function and chemical diversity of marine terpenoids, a new perspective on the evolutionary history of terpenoids, and on their role in the adaptive evolution of olfaction during the transition from aquatic to terrestrial life will be presented.