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51.
Several theories predict the evolution of bias in progeny sex ratio based on variations in maternal or offspring reproductive value. For mammals, however, tests of sex-bias theories have produced inconsistent results, and no clear patterns have emerged. Each theory is based on assumptions that are difficult to satisfy, and empirical tests require large data sets. Using a long-term study on bighorn sheep (Ovis canadensis), we identified several parameters that influence progeny sex ratio according to maternal state. For older females, progeny sex ratio was affected by an interaction between reproductive strategy and environmental conditions. When conditions were good, old females reproduced every year but minimized fitness costs by producing daughters. When conditions were poor, old females produced more sons but did not reproduce every year. Sons of older females were of similar mass to those born to younger females under poor conditions but were smaller and likely disadvantaged under good environmental conditions. For young and prime-aged females, progeny sex ratio was independent of environmental conditions. Environmental conditions and age should be considered when studying sex ratio bias, which appears to be a function of maternal state rather than of maternal condition. We suggest that a conservative reproductive strategy drives progeny sex ratio in older females according to the "cost of reproduction hypothesis." By manipulating offspring sex ratio, older females reduced the cost of reproduction and increased their expected fitness returns. 相似文献
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Julien Saada Olivier Parant Sylvie Kessler Jacqueline Aziza Marie France Sarramon 《黑龙江环境通报》2006,26(1):9-10
Congenital splenic cyst (CSC) is a rare condition, and only a few cases with prenatal diagnosis and no associated malformation have been reported. Spontaneous regression is possible in case of mild CSC (under 40 mm), but enlargement or secondary complications may lead to surgical treatment. We report, herein, two cases of isolated mild CSC with complete spontaneous postnatal regression. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Anne Pinton Julia Boubnova François Becmeur Pierre Kuhn Marie-Victoire Senat Julien Stirnemann Marianne Capelle Jonathan Rosenblatt Jérôme Massardier Pascal Vaast Gwenaelle Le Bouar Amélie Desrumaux Laure Connant Laetitia Begue Benoit Parmentier Franck Perrotin Alain Diguet Guillaume Benoist Charles Muszynski Aurélien Scalabre Norbert Winer Jean-Luc Michel Florence Casagrandre-Magne Jean-Marie Jouannic Denis Gallot Perrine Coste Mazeau Emmanuel Sapin Alexis Maatouk Anne-Hélène Saliou Loïc Sentilhes Florence Biquard Nicolas Mottet Romain Favre Alexandra Benachi Nicolas Sananès 《黑龙江环境通报》2020,40(8):949-957
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Scent-marking is a frequent behaviour of highly social ground squirrels and might play an important role in their social dynamics.
Female Columbian ground squirrels exhibit considerable scent-marking during the reproductive period. We examined how gestating
and lactating females responded to jugal gland scent-marks of same-sexed and opposite-sexed conspecifics with attention to
genetic relatedness and the geographical location of the territory of individuals. We tested the dear-enemy, threat-level
and kin-discrimination hypotheses to explain patterns of scent-marking. Females sniffed the scent of non-neighbouring males
significantly longer than other types of scent categories and tended to over mark the scent of females more than the scent
of males. Furthermore, females sniffed significantly longer at scents during gestation than during lactation. We concluded
that scent-marking mainly functioned in the defence of female territories and for protection of pups against infanticidal
females (threat-level hypothesis). Our results were also in accordance with the kin-discrimination hypothesis, because greater
attention was paid to the marks of non-kin females. Kin females might not pose an infanticidal threat, perhaps explaining
greater tolerance among related reproductive females. We concluded that scent-marking may be a relatively low-cost means of
territorial defence, as well as a means of communication of aspects of individual identity. 相似文献