Articulo Vibrisa

MARINE MAMMAL SCIENCE, 26(3): 733–743 (July 2010) C 2010 by the Society for Marine Mammalogy DOI: 10.1111/j.1748-7692.2009.00365.x

Morphological analysis of the bumpy profile of phocid vibrissae
CARLY C. GINTER1 FRANK E. FISH
Department of Biology, West Chester University, 750 S. Church Street, West Chester, Pennsylvania 19383, U.S.A. E-mail: ccginter@tamu.edu

CHRISTOPHER D. MARSHALLDepartment of Marine Biology and Wildlife and Fisheries Sciences, Texas A&M University, 5007 Avenue U, Galveston, Texas 77551, U.S.A.

Organisms rely on sensory systems to obtain information about their surroundings. The secondarily aquatic lifestyle required marine mammals to develop novel sensory modalities to operate in water. Phocid seals have three groups of vibrissae, mystacial, supraorbital,and rhinal, all of which occur only on the face of the animal (Ling 1977). All species of phocid seals except bearded (Erignathus barbatus) and monk (Monachus spp.) seals have bumps along hair shafts of their mystacial vibrissae (Ognev 1935, King 1983, Hyv¨ rinen and Katajisto 1984, Dehnhardt and Kaminski 1995, a Marshall et al. 2006). The vibrissae have an ellipsoidal cross-section with aregularly repeating sequence of crests and troughs to give a sinusoidal profile along their length. This morphology is not known to be present in the hairs of any other mammalian group. The presence of the bumps along the length of the vibrissae allude to three possible functions, including drag reduction, increased sensitivity, and reduced signal interference. These functions are not mutually exclusive.It has been hypothesized that the bumpy morphology of the vibrissae suggests potential hydrodynamic advantages for seals (Fish et al. 2008). The vibrissae vibrate at a frequency related to the flow of water over them as the seal swims (Hyv¨ rinen a and Katajisto 1984). The wavy profile of the vibrissae may passively modify the flow of water to reduce vibrations created by drag (Fish et al. 2008). Adecrease in the vibrations due to ambient environmental noise could make the vibrissae more sensitive to other flow stimuli. The wavy profile may be an adaptation that aids seals foraging in low visibility environments by allowing them to follow the change in water flow from vortex trails left by swimming prey (Hyv¨ rinen and Katajisto a 1984, Dehnhardt et al. 1998, 2001, Schulte-Pelkum et al. 2007).Humpback whale (Megaptera novaeangliae) flippers possess tubercles that create a bumpy profile along the leading edge (Winn and Reichley 1985). This morphology has been shown to
Current address: Department of Wildlife and Fisheries Sciences, Texas A&M University, College Station, Texas 77843, U.S.A.
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affect the hydrodynamiccharacteristics of the flipper to increase maneuverability during turning (Miklosovic et al. 2004, Fish et al. 2008). Despite possible hydrodynamic function and ecological implications, the basic morphology of the bumps along the vibrissae has not been characterized. Analysis of the vibrissae of phocids possessing this morphology would help elucidate whether the vibrissae have a sensory and hydrodynamicadvantage. The size, shape, and pattern of these bumps may determine their adaptive effectiveness as well as offer clues as to how these detect prey. Here, we describe the morphology of the bumps present on harp (Pagophilus groenlandicus), hooded (Cystophora cristata), and gray (Halichoerus grypus) seal vibrissae. For comparison, we examined E. barbatus vibrissae because this phocid is known to havevibrissae without bumps. Mystacial vibrissae from eight juvenile seals, five P. groenlandicus, two C. cristata, and one H. grypus, were analyzed. All samples were obtained, under permits held by CDM, from dead, beached animals that were necropsied at the University of Pennsylvania Veterinary School, New Bolton Center. Vibrissae were removed from the seals by cutting them off at the skin surface...