Pelage and Molting in Wild Mammals with Special Reference to Aquatic Forms
TL;DR: The pelage cycle must be regarded from the point of view of the whole process of follicular activity and fiber production, rather than simply the externally visible molt, if that unique mammalian characteristic, hair, is to be understood in its true biological perspective.
Abstract: Hairs are epidermal derivatives, the type, structure, and arrangement of which are related to the role of the mammalian pelage Hair follicles probably evolved from amphibian apidermal excrescences which became modified into sensory pits of the reptilelike ancestors of mammals Pelage affords insulation, is sensitive to external stimuli, may be modified for defense or display, assists in buoyancy and streamlining in water, and aids concealment on land The basic grouping of hair follicles by threes (trio group) appears almost to have been lost in the Pinnipedia, in which other anatomical adaptations to an aquatic habit include flattened guard hairs, loss of erector (arrector pili) muscles and modified cutaneous glands Periodic growth and replacement of the pelage is essential to survival The pelage cycle is closely related to the annual cycle with respect to seasonal requirements dictated by the environment, such as climate and life processes, particularly reproduction Different pelages occur at differ
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TL;DR: Optimisation of energy by aquatic mammals requires adaptations that reduce drag, and improve thrust production and efficiency, and changes in propulsive mode and appendage design are accomplished.
Abstract: Optimisation of energy by aquatic mammals requires adaptations that reduce drag, and improve thrust production and efficiency. Drag is minimised by streamlining the body and appendages. Highly derived aquatic mammals have body shapes close to the optimal hydrodynamic design for drag reduction. There is no conclusive evidence for specialised drag reduction mechanisms, although decreasing hair density is associated with reduced drag. Improvement in thrust production and efficiency is accomplished by changes in propulsive mode and appendage design. Semiaquatic mammals employ drag-based propulsion using paddles, whereas fully aquatic mammals use lift-based propulsion with hydrofoils. Because paddling generates thrust through half the stroke cycle, propulsive efficiency is low and energetic cost is high compared with that for mammals using hydrofoils. Lift-based swimming is a rapid and high-powered propulsive mode. Oscillations of the hydrofoil generate thrust throughout the stroke cycle. For cetaceans and pinnipeds, propulsive efficiency is approximately 80%, and transport cost is below that of semiaquatic mammals. Behavioural adaptations help minimise energy expenditure by swimming mammals. Submerged swimming avoids increased drag from energy lost in formation of surface waves. Porpoising and wave riding, characteristic of dolphins, can reduce the transport costs, allowing for longer-duration swimming at high speeds.
211 citations
Cites background from "Pelage and Molting in Wild Mammals ..."
...For semiaquatic mammals, non-wettable fur provides buoyancy by an entrapped layer of air (Johansen 1962; Ling 1970; Dagg and Windsor 1972; Esher et al. 1978; Fish and Stein 199 1)....
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...The lack of arrector pili muscles in seals and sea otter permits the pelage to lie flat in water, minimising resistance to swimming (Ling 1970)....
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TL;DR: Northern elephant seal females and pups were observed during four breeding seasons at Ano Nuevo Tstand, California and the probability of separation was increased by high numbers of females and disturbances created by intrusions of breeding hulls into the harem.
Abstract: Northern elephant seal females and pups were observed during four breeding seasons at Ano Nuevo Tstand, California. Six to seven days after a female arrived on the rookery she gave birth to a single pup which she nursed for four weeks. Estrus began 24 days after parturition and lasted an average of four days. Females spent a total of 34 days on the rookery before returning to sea. The only other time females came ashore was to moult, a period which lasted a few weeks. Most births occurred in the harem at night during the last two weeks of January. Cephalic presentations were more frequent than caudals (62% vs. 38%) and both were equally rapid. The placenta was delivered immediately after the pup or within an hour after birth. Stillbirths were infrequent and premature pups were never observed. The sex ratio was 49.4 males to 50.5 females. Eight females gave birth for the first time during their third year but most females are believed to give birth later. Three females gave birth on a different rookery than their own birthplace. The time of parturition from year to year was very consistent in individual females. Newborn pups weighed 65 lbs at birth and were 60 inches long. They are precocial and suckled for about four weeks before being weaned. Weaners moulted their natal pelage at four to six weeks of age, a time when they began entering the water. Most weaners left the rookery headed north during the month of April. Females accepted a pup by allowing it to nurse and rejected alien pups by biting them. Females emitted two vocalizations : a pup attraction call and a threat vocalization. Pups emitted a single vocalization which functioned in several situations. Scventy-two percent of the females observed nursed their own pups to weaning and rejected most of the suckling attempts of alien pups. A few females nursed an alien pup in addition to their own. Twenty-six percent of the females became separated from their pups or their pups died. One third of these females adopted an alien pup. Females that gave birth, but did not nurse for several days, did not copulate. The frequency and duration of suckling increased as pups developed. Pups attempted to suckle any available female but were rejected by most alien females. Sixty percent of marked pups suckled their mothers. The remaining forty percent were separated from their mothers and most of them died. Those that survived were adopted by an alien female or were suckled by several different females each day. Pup mortality at Ano Nuevo Island was very consistent over the four year period, ranging from 13.0% to 14.5%. Most mortalities were socially induced; pups separated from their mothers starved or were injured by adult males and females. The probability of separation was increased by high numbers of females and disturbances created by intrusions of breeding hulls into the harem.
177 citations
TL;DR: The finding suggests that the duration of circadian melatonin elevation is the critical parameter determining its effect not only on the gonads, but also on the pelage, and this study investigated whether circulating FSH levels, known to affect testicular function, and PRL levels, which have been shown to affect pelage color, might be affected differently by 14L:10D.
Abstract: Testicular function and pelage color are regulated by photoperiod in the Djungarian hamster. To investigate the critical daylengths of these functions, adult male hamsters were exposed to one of four photoperiods: 16 h of light, 8 h of darkness (16L:8D), 14L:10D, 12L:12D, or 10L:14D. 10L:14D and 12L:12D induced the winter molt and testicular regression, in contrast to 14L:10D which induced only the latter response, and 16L:8D which maintained the summer pelage and large testes. Melatonin injections administered 4, 2, or 0 h before lights-off to hamsters exposed to 16L:8D mimicked the effects in hamsters exposed to 10:14D, 12L:12D or 14L:10D, respectively, on pelage color and testicular weight. Based on previous observations, the elevated circulating melatonin levels resulting from these injections were expected to extend the endogenous melatonin peak. Thus, this finding suggests that the duration of circadian melatonin elevation is the critical parameter determining its effect not only on the gonads, but also on the pelage. Since 14L:10D induced testicular regression but not the winter molt, this study also investigated whether circulating FSH levels, known to affect testicular function, and PRL levels, which have been shown to affect pelage color, might be affected differently by 14L:10D. Both FSH and PRL levels were found to be suppressed in 14L:10D hamsters compared to those in 16L:8D hamsters, although the interval between the initial decrease and eventual recovery was less than that in 10L:14D hamsters. Thus, the differential responses of the pelage and gonads to 14L:10D do not appear to be based on selective suppression of FSH in this photoperiod. However, different responses to 14L:10D compared to 10L:14D may be related to the shorter period of suppression of both PRL and FSH by the 14L:10D daylengths.
132 citations
TL;DR: Energy expenditures suggest that, similar to data for harbour seals, the moult period is a time of relatively low energy expenditure.
Abstract: Northern elephant seals, Mirounga angustirostris, undergo an annual moult during which they shed all of their pelage and underlying epidermis. Moulting takes place on land and lasts a mean of 32.0±6.6 days. During this time the mean mass loss of adult females was 24.7±6.1%. Mean body composition at arrival (25.6±4.8%fat) did not differ significantly from that at departure (24.9±3.2%fat). Fat catabolism accounted for 93.6%of derived energy and 41%of mass lost. Approximately 3.5%of total mass loss was associated with the shedding of the pelage and epidermis. Moulting female northern elephant seals express an average daily metabolic rate of 2.0±0.6 times that predicted for adult terrestrial mammals. This energy demand was met by losing 3.0 kg d-1 of total body mass. These energy expenditures suggest that, similar to data for harbour seals, the moult period is a time of relatively low energy expenditure.
113 citations
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TL;DR: Insulation measurements on raw skins from 16 arctic and 16 tropical mammals are given and there is, as would be expected, a good correlation between the thickness of the fur and the insulation.
Abstract: Insulation measurements on raw skins from 16 arctic and 16 tropical mammals are given. There is, as would be expected, a good correlation between the thickness of the fur and the insulation. The smaller arctic mammals (weasels, lemmings) have much less insulation than the larger and overlap many of the tropical forms. From the size of a fox to the size of a moose there is no correlation between insulation and body size, they all have about the same insulation per surface area. When submerged in ice water, seal blubber retains about the same good insulation, as compared with measurements taken in 0° C. air. In the polar bear, heat transfer through the fur increases 25-50 times when submerged, because of complete wetting of the skin surface and absence of blubber. The beaver is slightly better off when submerged, as it retains an insulating layer of air in the fur next to the skin.
576 citations
TL;DR: Adaptive coloration in animals by Dr. Hugh B. Cott as mentioned in this paper is a classic example of such a work, and it has been widely used in the field of biology and psychology.
Abstract: THIS excellent work, eagerly awaited for many years, will be most welcome to naturalists, even, we may hope, to the few who have hitherto rejected the Darwinian interpretation which the author has here supported by a mass of additional evidence based on his own observations and those of very many others. Dr. Julian Huxley, in his introduction, refers to one of these critics, the American zoologist, A. F. Shull, who writes in contemptuous terms of the whole subject. To this Huxley replies: “Dr. Cott, in this important book, has turned the tables with a vengeance on objectors of this type. He has shown that it is they who are the armchair critics, or, one might say, the laboratory-bench critics. Had they taken the trouble to acquaint themselves with even a fraction of the relevant facts to be found in nature, they could never have ventured to enunciate such sweeping criticisms”. Adaptive Coloration in Animals By Dr. Hugh B. Cott. Pp. xxxii + 508 + 49 plates. (London: Methuen and Co., Ltd., 1940.) 40s. net.
427 citations
TL;DR: In this article, the authors propose a method to solve the problem of the problem: this article...,.. ].. ).. ]... )...
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382 citations
TL;DR: Evidence was obtained which suggested that the migratory pigment-forming cells, the melanophores, take their origin from the neural crest, as in other vertebrates, e.g., amphibians and birds.
Abstract: testing the pigment-forming potency of various portions of mouse embryos of a potentially pigmented (black) strain, evidence was obtained which suggested that the migratory pigment-forming cells, the melanophores, take their origin from the neural crest, as in other vertebrates, e.g., amphibians and birds.The results of grafting a variety of embryonic mouse tissues, such as skin ectoderm plus the underlying mesoderm, somites with and without the adjacent neural tube, limb buds and prospective limb buds, from various body levels, showed
363 citations
TL;DR: In an address delivered some years ago to the Scottish Natural History Society, Sharpey-Schafer as mentioned in this paper made the following comments, "the regularity with which migration occurs, indicates that the exciting cause must be regular".
Abstract: THAT light is a factor of prime importance in the inauguration or stimulation of bird migration, has been suggested by many authors from the days of Seebohm onwards. While many of the suggestions will not bear close investigation, at least one very attractive view has been put forward by Sir E. Sharpey-Schafer. In an address delivered some years ago to the Scottish Natural History Society1 he makes the following comments, “the regularity with which migration occurs, indicates that the exciting cause must be regular. There is no yearly change, outside the equatorial zone, that occurs so regularly in point of time as the change in the duration of daylight. On this ground this may well be considered a determining factor in migration, and it has the advantage over other suggested factors that it applies to the northerly as well as to the southerly movement.” He says further “That it [migration] is a result of developmental changes in the sexual organs is improbable.”
288 citations