Meeting Abstract
Vibrissae, or whiskers, are largest among pinnipeds and essential for prey capture. Behavioral data from pinniped and rodent vibrissa studies indicate that functional differences exist between medial and lateral vibrissae. However, comparative data are lacking and current pinniped studies have only focused on large, lateral vibrissae. Consequently, we investigated the medial-to-lateral innervation and microanatomy of harp seal (Pagophilus groenlandicus) vibrissal Follicle-Sinus Complexes (F-SCs). Harp seals possessed 88-105 F-SCs, which exhibited a tripartite organization. Hair shafts were circular medially but became more elliptical laterally. Medial F-SCs had symmetrical dermal capsule thicknesses and distributions of major branches of the deep vibrissal nerve, but these symmetries diminished in lateral F-SCs. Medial-to-lateral axon counts ranged from 550 ± 97 to 1,632 ± 173 axons/F-SC, respectively, indicating a total of 117,235 axons/snout. Lateral F-SCs alone possessed a mean of 1,533 ± 192 axons, similar to counts in other pinniped vibrissal innervation studies. Conventional studies that only examine lateral F-SCs likely overestimate total innervation by ~20%. Moreover, we counted axons with and without silver staining and determined that unstained sections yielded more accurate and ~10% greater axon counts. Consequently, conventional studies likely only overestimate innervation by ~10%. The relationship between axon count and F-SC surface area was non-linear, presumably from mechanoreceptors reaching carrying capacity, and axon densities were consistent across the snout. Our data agree well with behavioral research on pinnipeds and rodents that documents functional compartmentalization between micro-(medial) and macrovibrissae (lateral).
