Sex-biased maternal expenditure in Rocky Mountain bighorn sheep |
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Authors: | John T Hogg Christine C Hass Donald A Jenni |
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Institution: | (1) Division of Biological Sciences, University of Montana, 59812 Missoula, MT, USA;(2) Present address: Craighead Wildlife-Wildlands Institute, 5200 Upper Miller Creek Road, 59803 Missoula, MT, USA;(3) Present address: Department of Biology, University of North Dakota, 58202 Grand Forks, ND, USA |
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Abstract: | Summary We examined maternal energy expenditure in Rocky Mountain bighorn sheep to test the hypothesis (Trivers and Willard 1973) that individual sons in polygynous mammals should obtain a larger maternal subsidy. In accord with theory, males weighed more at birth (an index of relative prenatal expenditure), tended to suckle more between 40 and 100 days of age (an index of relative postnatal expenditure) and imposed greater delays on their mothers' return to estrus in the subsequent breeding season (an index of relative total preweaning expenditure). Mothers rather than offspring appeared to have primary control over postnatal expenditure. The effect of maternal reproductive effort on return to estrus was cumulative over a period of 3–5 years so that ewes making relatively large expenditures gave birth progressively later. Ewe and lamb mortality was associated with late conception in the previous rut. Thus, differential reproductive effort by ewes in this population appeared to entail a fitness cost involving reductions in both offspring and maternal survivorship.
Correspondence to: J.T. Hogg at the present address |
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