Abstract
IntroductionWhile olfaction is one of the most important senses in most terrestrial mammals, it is absent in modern toothed whales (Odontoceti, Cetacea). Furthermore, behavioral evidence suggests that gustation is very limited. In contrast, their aquatic sistergroup, baleen whales (Mysticeti) retain small but functional olfactory organs, and nothing is known about their gustation. It is difficult to investigate mysticete chemosensory abilities because experiments in a controlled setting are impossible.ResultsHere, we use the functional regionalization of the olfactory bulb (OB) to identify the loss of specific olfactory functions in mysticetes. We provide the whole-genome sequence of a mysticete and show that mysticetes lack the dorsal domain of the OB, an area known to induce innate avoidance behavior against odors of predators and spoiled foods. Genomic and fossil data suggest that mysticetes lost the dorsal domain of the OB before the Odontoceti-Mysticeti split. Furthermore, we found that all modern cetaceans are revealed to have lost the functional taste receptors.ConclusionThese results strongly indicate that profound changes in the chemosensory capabilities had occurred in the cetacean lineage during the period when ancestral whales migrated from land to water.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-014-0002-z) contains supplementary material, which is available to authorized users.
Highlights
While olfaction is one of the most important senses in most terrestrial mammals, it is absent in modern toothed whales (Odontoceti, Cetacea)
Genomic and fossil data suggest that mysticetes lost the dorsal domain of the olfactory bulb (OB) before the Odontoceti-Mysticeti split
These results strongly indicate that profound changes in the chemosensory capabilities had occurred in the cetacean lineage during the period when ancestral whales migrated from land to water
Summary
While olfaction is one of the most important senses in most terrestrial mammals, it is absent in modern toothed whales (Odontoceti, Cetacea). Terrestrial mammals usually have a well-developed sense of smell that can detect various odors using four kinds of G-protein coupled receptors (GPCRs) encoded by different multigene families to each other: olfactory receptors (ORs), trace amine-associated receptors (TAARs) and two types of vomeronasal receptors (V1Rs and V2Rs) [1]. This sense was greatly reduced in the ancestors of modern cetaceans [2]. D domain-ablated mice (ΔD mice) fail to show innate avoidance behavior against predator odors and spoiled smells [16]
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