PicardThomasFesta-BianchetEtAl1999

Référence

Picard, K., Thomas, D.W., Festa-Bianchet, M., Belleville, F., Laneville, A. (1999) Differences in the thermal conductance of tropical and temperate bovid horns. Ecoscience, 6(2):148-158.

Résumé

Bovid horns consist of a highly vascularized bone core covered by a keratin sheath which seems to offer limited resistance to heat flow. Based on dynamic cooling curves measured for inverted horns filled with warm water, we developed estimates of the thermal conductance of keratin and the coefficients of convective heat transfer at the water-to-sheath and the sheath-to-air boundaries to allow us to quantify heat flux through the horn sheath. Coupled with measurements of the internal and external horn dimensions, we constructed a simplified conceptual model of sheaths from 68 horns of 14 bovid species to test the prediction that the horns of temperate bovid species offer greater resistance to heat flux than the horns of tropical bovids. The specific heat capacity of the keratin sheath was 1.53 ± 0.07 (SD) J g-1°C-1. The coefficient of conductive heat transfer for keratin was 6.30 x 10-3 ± 0.30 x 10-3 (SD) W cm-1°C-1. We estimated the coefficients of convective heat transfer at the water-to-sheath and the sheath-to-air interfaces to be 8.79 x 10-3 ± 5.20 x 10-3 W cm-2°C-1 and 2.49 x 10-3 ± 1.98 x 10-3 W cm-2°C-1, respectively. A reduction in the size of the bone core and overlying vascular bed and an increase in the thickness of the keratin sheath in temperate bovids acted to reduce the surface area through which heat was lost to the environment. Because the surface-specific thermal conductances of temperate sheaths were lower than those of tropical sheaths, we estimate that a temperate bovid having horns of the same length and external surface as a tropical bovid would experience only 75.7% of the heat loss when facing a thermal gradient of 20°C. We argue that differences in horn morphology between temperate and tropical Bovidae appear to have evolved as adaptations to restrict heat loss in the former while facilitating heat loss in the latter group.

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@ARTICLE { PicardThomasFesta-BianchetEtAl1999,
    AUTHOR = { Picard, K. and Thomas, D.W. and Festa-Bianchet, M. and Belleville, F. and Laneville, A. },
    TITLE = { Differences in the thermal conductance of tropical and temperate bovid horns },
    JOURNAL = { Ecoscience },
    YEAR = { 1999 },
    VOLUME = { 6 },
    PAGES = { 148-158 },
    NUMBER = { 2 },
    NOTE = { 11956860 (ISSN) Cited By (since 1996): 4 Export Date: 26 April 2007 Source: Scopus Language of Original Document: English Correspondence Address: Thomas, D.W.; Grp. de rech. en ecol., nut. et enr.; Departement de Biologie; Universite de Sherbrooke Sherbrooke, Que. J1K 2R1, Canada; email: d.thomas@courrier.usherb.ca References: Bakken, G.S., An improved method for determining thermal conductance and equilibrium body temperature with cooling curve experiments (1976) Journal of Thermal Biology, 1, pp. 169-175; Bubenik, G.A., Bubenik, A.B., (1990) Horns, Pronghorns, and Antlers: Evolution, Morphology, Physiology, and Social Significance, , Springer-Verlag, New York; Eccles, T.R., Shackleton, M., Correlates and consequences of social status in female bighorn sheep (1986) Animal Behavior, 34, pp. 1392-1401; Essop, M.F., Harley, E.H., Baumgarten, I., A molecular phytogeny of some Bovidae based on restriction-site mapping of mitochondrial DNA (1997) Journal of Mammalogy, 78, pp. 377-386; Estes, R.D., The significance of horns and other male secondary sexual characters in female bovids (1991) Applied Animal Behavioral Science, 29, pp. 403-451; Festa-Bianchet, M., Jorgenson, J.T., King, W.J., Smith, K.G., G., K., Wishart, W.D., The development of sexual dimorphism: Seasonal and lifetime mass changes in bighorn sheep (1996) Canadian Journal of Zoology, 74, pp. 330-342; Gates, D.M., (1980) Biophysical Ecology, , Springer-Verlag, New York; Geist, V., (1971) Mountain Sheep, , University of Chicago Press, Chicago, Illinois; Geist, V., The evolutionary significance of mountain sheep horns (1966) Evolution, 20, pp. 558-566; Hogg, J.T., Copulatory tactics in relation to sperm competition in Rocky Mountain bighorn sheep (1988) Behavioral Ecology and Sociobiology, 22, pp. 49-59; Kreith, F., (1993) Principles of Heat Transfer, , Harper \& Row, New York; Locati, M., Lovari, S., Clues for dominance in female chamois: Age, weight, or horn size? (1991) Aggressive Behavior, 17, pp. 11-15; Nowak, R.M., Paradiso, J.L., (1983) Walker's Mammals of the World.- Volume II. Fourth Edition, 2. , The Johns Hopkins University Press, Baltimore, Maryland; Picard, K., Thomas, D.W., Festa-Bianchet, M., Lanthier, C., Bovid horns: An important site for heat loss during winter? (1994) Journal of Mammalogy, 75, pp. 710-713; Picard, K., Festa-Bianchet, M., Thomas, D.W., The cost of horniness: Heat loss may counter sexual selection for large horns in temperate bovids (1996) E?coscience, 3, pp. 280-284; Ricklefs, R.E., Applications of phylogenetically independent contrasts: A mixed progress report (1996) Oikos, 77, pp. 167-172; Taylor, C.R., (1963) The Thermoregulatory Function of the Horns of the Family Bovidae, , Ph. D. Thesis, Harvard University, Boston, Massachusetts; Taylor, C.R., The vascularity and possible thermoregulatory function of horn in goats (1966) Physiological Zoology, 39, pp. 127-139; Taylor, R.A., (1962) Characteristics of Horn Growth in Bighorn Sheep Rams, , M. Sc. Thesis. Montana State University, Missoula, Montana; Wathen, R.M., Mitchell, J.W., Porter, W.P., Heat transfer from animal appendage shapes: Cylinders, arcs, and cones (1974) Journal of Heat Transfer, Transactions of the American Society of Mechanical Engineering, 96, pp. 536-540. },
    ABSTRACT = { Bovid horns consist of a highly vascularized bone core covered by a keratin sheath which seems to offer limited resistance to heat flow. Based on dynamic cooling curves measured for inverted horns filled with warm water, we developed estimates of the thermal conductance of keratin and the coefficients of convective heat transfer at the water-to-sheath and the sheath-to-air boundaries to allow us to quantify heat flux through the horn sheath. Coupled with measurements of the internal and external horn dimensions, we constructed a simplified conceptual model of sheaths from 68 horns of 14 bovid species to test the prediction that the horns of temperate bovid species offer greater resistance to heat flux than the horns of tropical bovids. The specific heat capacity of the keratin sheath was 1.53 ± 0.07 (SD) J g-1°C-1. The coefficient of conductive heat transfer for keratin was 6.30 x 10-3 ± 0.30 x 10-3 (SD) W cm-1°C-1. We estimated the coefficients of convective heat transfer at the water-to-sheath and the sheath-to-air interfaces to be 8.79 x 10-3 ± 5.20 x 10-3 W cm-2°C-1 and 2.49 x 10-3 ± 1.98 x 10-3 W cm-2°C-1, respectively. A reduction in the size of the bone core and overlying vascular bed and an increase in the thickness of the keratin sheath in temperate bovids acted to reduce the surface area through which heat was lost to the environment. Because the surface-specific thermal conductances of temperate sheaths were lower than those of tropical sheaths, we estimate that a temperate bovid having horns of the same length and external surface as a tropical bovid would experience only 75.7% of the heat loss when facing a thermal gradient of 20°C. We argue that differences in horn morphology between temperate and tropical Bovidae appear to have evolved as adaptations to restrict heat loss in the former while facilitating heat loss in the latter group. },
    KEYWORDS = { Bovidae Cold adaptation Heat flow Horns Thermal conductance heat flow horn thermal conductivity ungulate },
    OWNER = { brugerolles },
    TIMESTAMP = { 2007.12.05 },
}

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