Meeting Abstract
The vibrissal (whisker) system is present in nearly all mammals and is especially important in deep-diving mammals. Pinnipeds (seals, sea lions, walrus) have highly innervated whiskers, indicating they serve as important sensory structures. Vibrissae are needed for foraging and thus it is vital to maintain their functionality under all environmental conditions. In pinnipeds studied thus far, each vibrissal unit includes a follicle sinus complex characterized by a three-part blood sinus system: the upper cavernous sinus (UCS), ring sinus (RS), and lower cavernous sinus (LCS). The UCS is unique to pinnipeds and lacks innervation. Based on this, we hypothesize that the UCS plays a thermoregulatory role, insulating temperature-dependent mechanoreceptors. Our objectives were (1) to measure and compare the relative lengths of the three sinuses (UCS, RS, and LCS) among three pinniped species and (2) to examine the UCS as a thermoregulatory structure. To do this, we measured and compared the relative lengths of the UCS in deep-diving polar Weddell seals (Leptonychotes weddellii, n=6), deep-diving temperate northern elephant seals (Mirounga angustirostris, n=4), and shallow-diving temperate harbor seals (Phoca vitulina, n=2). Individual vibrissal follicles were collected and histologically processed from animals that died in the wild or during rehabilitation efforts. We predicted that the species faced with the coldest environment both at depth and in air (i.e., Weddell seals) would have the longest UCS. Our preliminary results suggest a positive correlation between the total sinus length and the average UCS length. This represents the first study to characterize the microstructures of the vibrissal system in Weddell seals and the first study to investigate the UCS as a thermoregulatory structure.
