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Variations in the birth sex ratio and neonatal mortality in a natural herd of horses 总被引:3,自引:0,他引:3
Anne-Marie Monard Patrick Duncan Hervé Fritz Claudia Feh 《Behavioral ecology and sociobiology》1997,41(4):243-249
Variations in birth sex ratios and sex differences in juvenile mortality occur in a number of mammalian species, and in many
cases have been linked to resource availability. Most of these biases in offspring sex ratios concern polygynous species with
pronounced sexual dimorphism, and where females only are philopatric. Data on species with unusual life-history strategies,
such as slight sexual dimorphism or dispersal by both sexes, are of particular interest. In this study of a natural herd of
horses (Equus caballus) which experienced an eruptive cycle, and therefore a period of nutritional stress, male offspring had higher neonatal mortality
rates in nutritionally poor years than in good ones, whereas “year quality” had no effect on the mortality of female offspring;
year quality could therefore be used by mares as predictor of sex-specific offspring survival. We show that the environmental
conditions that predicted lower survival of males were negatively related to their production: the birth sex ratio the following
year was female-biased; and mares were less likely to produce a son when they had produced a son the preceding year. There
was no significant effect of mother's parity, age or rank, or the timing of conception or birth on offspring sex ratios. The
mechanism leading to biases in the birth sex ratio could have been the loss of male embryos by mares that did not foal. As
there was no evidence for selective abortion of male foetuses in females that did foal the next year, it is not necessary
to invoke maternal adjustment, though this remains a possibility. Finally, there was a suggestion that male offspring were
more costly to raise than females, since mothers that reared a son in poor years tended to experience an increase in the interbirth
interval between their two subsequent offspring.
Received: 28 December 1996 / Accepted after revision: 27 July 1997 相似文献
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Heidelore Fiedler Gerd Rippen Susanne Sievers Peter Friesel Birgit Gras Christoph Lau Thomas Reich Uwe Schacht Roland Schwörer Hansjörg F. Wesp Otto Hutzinger Fritz Vahrenholt 《Environmental Sciences Europe》1997,9(3):131-135
The sources and reservoirs of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) in the city of Hamburg, Germany, in the year 1992 were identified and quantified combining analytical data of PCDD/PCDF with statistical data on annual fluxes of materials and products. Fluxes and amounts of PCDD/PCDF were estimated for the environmental compartments water, air, and soil. Dioxin emissions originating from industrial, commercial or private activities were also calculated. Together with the analysis of the specific regional nutrition data, the human exposurevia the various pathways could be determined. It could be shown that the total PCDD/PCDF intake of individuals in Hamburg was about the same as the national average. High annual fluxes of PCDD/PCDF connected with the trade of industrial products and the waste management and disposal: system in Hamburg obviously had no influence on the human intake of PCDD/PCDF. 相似文献
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O. Baschin B. Brandt Fritz Braun Bruno Schulz M. v. Laue 《Die Naturwissenschaften》1923,11(25):497-500
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