Otters cavorting in the water is a scene with which we’re allfamiliar. Yet, unlike many other mammals that spend a considerableamount of time in the water–polar bears, seals, dolphins, andwhales–river otters do not have a thick layer of body fat to keep warm.They rely, instead, on a few unique adaptations; namely, their fur andthe densely packed layer of specially adapted underhairs.
Usingscanning electron microscopy and polarizing light microsopy, John W.Weisel, PhD, Professor of Cell and Developmental Biology at theUniversity of Pennsylvania School of Medicine, and colleagues, examinedthe structure of these hairs for clues to their exceptional insulationabilities. (Click on the thumbnail to view full-size images). Theyfound that the cuticle surface structure of the underhairs and base ofthe less-abundant guard hairs are distinctively shaped to interlock,with wedge-shaped fins or petals fitting into wedge-shaped groovesbetween fins of adjacent hairs. Weisel and colleagues report theirfindings in the Canadian Journal of Zoology.
Weisel and ResearchSpecialist Chandrasekaran Nagaswami, MD, also in Penn’s Department ofCell and Developmental Biology, usually work on defining the physicalproperties of blood clots and applying this knowledge to find bettertreatments for heart disease. Two years ago when Weisel, an avid hiker,climber, and white-water kayaker, took a month of his sabbatical yearto study wolves–a life-long interest–on Isle Royale National Park inLake Superior, Michigan, he also collected hair samples from theisland’s mammals—including wolves, moose, and otters. (The ecologicalstudies of wolves and moose on Isle Royale, which started in 1959, arepart of the longest-running animal ecology study in the world. IsleRoyale has been a training ground for many ecologists, and lessonslearned here have been applied to the re-introduction of wolves toYellowstone National Park.)
Weisel examined wolf prey hair withlight and electron microscopy with the idea of accurately identifyingwolf diet from wolf scat. “While we have engaged molecular biologistsin studies of animal genetics and isotope dynamics, John is the firststructural molecular biologist that we have worked with,” says wildlifebiologist Rolf Peterson from Michigan Technological University(Houghton, Mich.), who has spent the last three decades doing fieldresearch on Isle Royale. “It was a delight to learn about importantbasic features of animal hair that facilitate their unique lifestyles.”
“Mosthair from animals has a distinctive pattern, which is how we candistinguish one species from another,” says Weisel. “But otter hair isso different that it caught my attention.” The fins of one hair looselyinsert into the grooves between fins of an adjacent hair, thuspermitting the hairs to form a web-like pattern that keeps water fromthe otter’s skin and decreases heat loss. Also, the grooves betweenfins trap air bubbles, which help increase the thermal insulation ofthe otter’s coat. Indeed, biologists have observed otters activelyblowing air bubbles into their fur while grooming, and their energeticrolling catches air in their fur. “The air insulates like a downjacket,” explains Weisel.
A common otter behavior, next to theirplayfulness, is their constant grooming. This behavior is anotherimportant aspect of an otter’s heat-sparing abilities. In addition tothe interlocking structure of the underhairs, these hairs are coatedwith a thin layer of body oil from the otter’s sebaceous glands, thusproviding another barrier to water. The fins of the underhairs are alsoaligned away from the body, which is consistent with the direction inwhich otters run their paws through their hair during thisself-grooming, thereby ensuring that their claws do not get caught onthe fin-like projections.
Weisel is continuing these studies ofmammal hair in his spare time and has returned to Isle Royale oncesince his sabbatical, doing radio telemetry of radio-collared wolvesand collecting samples of their scat for DNA analysis.
“Idiscovered that it can be very enjoyable and stimulating to expand yourscientific horizons beyond the familiar, and even get to take a‘busman’s holiday’ in a beautiful place with wonderful people,enriching your scientific and personal life,” says Weisel of hisexperiences away from the bench. “There are still a great many newthings to learn, but some approaches and ideas from one field can beuseful in another.”
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