A Comparative Genomics Approach to Understanding the Evolution of Olfaction in Cetaceans

Area of Science:

• Evolutionary biology
• Comparative genomics
• Sensory systems evolution

Background:

• Cetacean evolution involved a major transition from terrestrial to marine environments, impacting sensory systems.
• The role of olfaction in baleen whale (mysticete) evolution remains poorly understood.
• Toothed whales (odontocetes) lack olfactory anatomical features, but the status of olfaction in mysticetes is unclear.

Purpose of the Study:

• To investigate the evolutionary history of olfaction in cetaceans.
• To determine if baleen whales have retained olfactory capabilities.
• To identify when olfactory pressures diverged within the cetacean lineage.

Main Methods:

• Examined eight genes involved in olfactory signal transduction and chaperones.
• Screened eight mysticete genomes for inactivating mutations and selective pressures.
• Tested evolutionary models of olfaction in cetaceans.

Main Results:

• All eight examined genes were intact in all eight mysticete genomes.
• In contrast, inactivating mutations were found in odontocete homologs of multiple genes.
• Results support a model of specifically reduced olfaction in the odontocete lineage.

Conclusions:

• Olfactory ability was likely reduced in toothed whales after their divergence from stem cetaceans.
• Baleen whales appear to have maintained their sense of smell.
• This study clarifies the evolutionary trajectory of olfaction within the cetacean lineage.