What are olfaction and gustation, and do all animals have them?

Area of Science:

• Comparative physiology
• Neuroethology
• Sensory biology

Background:

• Vertebrates have distinct olfaction and gustation, conserved neuroanatomically.
• These senses function in aquatic and terrestrial environments.
• Invertebrate chemical senses are often termed olfaction/gustation but lack homology.

Purpose of the Study:

• To compare chemical senses across diverse animal groups.
• To evaluate the classification of invertebrate chemical senses.
• To propose criteria for categorizing chemical senses.

Main Methods:

• Comparative analysis of anatomical and physiological properties.
• Examination of peripheral sensory cells.
• Analysis of neural processing centers (neuropil organization).
• Review of molecular receptor specificity and function.

Main Results:

• Vertebrate olfaction and gustation are distinct.
• Invertebrate chemical senses show convergent evolution, not homology.
• Existing terminology for invertebrate senses is problematic.
• Proposed categorization includes olfaction, oral/extra-oral gustation, or chemoreception.

Conclusions:

• Chemical senses vary significantly across animal taxa.
• Homology, not just function, is key for classification.
• A unified or refined terminology for chemical senses is needed.
• Sensory cell type, neural organization, and receptor specificity are crucial for categorization.