Morphometric analysis of the elasmobranch olfactory rosette.

Area of Science:

• Comparative anatomy
• Ichthyology
• Sensory biology

Background:

• Elasmobranch olfactory rosettes exhibit diverse morphologies, but the functional implications remain unclear.
• Understanding this diversity is crucial for elasmobranch sensory ecology and evolutionary studies.

Purpose of the Study:

• To quantify olfactory rosette morphology in elasmobranchs using dissection and diceCT.
• To analyze trends in rosette morphology within a phylogenetic context.
• To compare the efficacy of dissection and diceCT for olfactory rosette analysis.

Main Methods:

• Morphometric analysis of dissected olfactory rosettes from 14 elasmobranch species.
• Phylogenetic principal component analysis (pPCA) to investigate morphological trends.
• Diffusible iodine-based contrast-enhanced computed tomography (diceCT) for in situ imaging of olfactory capsules in four Carcharhiniformes species.

Main Results:

• Significant interspecific variation was found in olfactory rosette fineness ratio and lamellar count, which were positively correlated.
• The first two principal components of the pPCA explained 82% of the variation, driven by fineness ratio and lamellar count.
• DiceCT provided comparable results to dissection for rosette structure and volume, validating it as a non-destructive imaging method.

Conclusions:

• Olfactory rosette morphology in elasmobranchs is species-specific and not directly influenced by body size.
• DiceCT is a reliable method for in situ analysis of olfactory organ morphology.
• These findings provide a foundation for future 3D modeling and hydrodynamic studies of elasmobranch olfaction.