Male-biased sex ratio in litters of Alpine marmots supports the helper repayment hypothesis
Male-biased sex ratio in litters of Alpine marmots supports the helper repayment hypothesis
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DOI：
10.1093/beheco/11.5.507
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发表时间：
2000-09-01
影响因子：
2.4
通讯作者：
Till-Bottraud, I
中科院分区：
文献类型：
--
作者：
Allainé, D;Brondex, F;Till-Bottraud, I
在法国阿尔卑斯旱獭种群（旱獭）中，断奶时的性别比例偏向于雄性。这种偏见似乎在出生时就存在。根据费雪的平均分配原则，这意味着生女儿的成本应该高于生儿子。由于高山旱獭可以被认为是一种合作繁殖物种，我们研究了儿子和女儿之间的差异成本是否可以用帮助者回报假说来解释。高山土拨鼠在冬眠期间使用社会体温调节，使幼崽能够更好地度过冬天。在研究种群中，幼鱼在冬季的存活率随着群体规模的增加而增加。更确切地说，冬季幼鱼的存活率随着冬眠组中从属雄鱼的数量和比例的增加而增加，但与从属雌鱼的数量无关。由于我们的研究结果不支持其他假说来解释在出现时观察到的后代性别比偏差，我们得出结论，帮助者回报假说是解释观察到的高山旱獭后代性别比偏差的最佳候选人。通过参与社会体温调节，从属雄性可能会偿还从父母那里得到的部分投资，从而降低生产成本。我们认为，只有下属的雄性才会帮助，因为它们可以获得直接的健康利益，而下属的雌性可能只期望从帮助中获得间接的健康利益。最后，每个亲本的后代性别比是雄性偏倚的，但母亲根据自己的表型状况调整其窝的大小和性别组成，正如特里弗斯-威拉德假设所期望的那样。
In a French population of Alpine marmots (Marmota marmota), the sex ratio at weaning was biased in favor of males. This bias also seemed to exist at birth. Under Fisher's equal allocation principle, this means that daughters should be more costly to produce than sons. Because the Alpine marmot can be considered a cooperative breeding species, we investigated whether the differential cost between sons and daughters may be explained by the helper repayment hypothesis. The Alpine marmot uses social thermoregulation during hibernation, allowing juveniles to better survive over winter. In the study population, juvenile survival during winter increased with group size. More precisely, juvenile survival during winter increased with the number and with the proportion of subordinate males in the hibernating group, but juvenile survival did not depend on the number of subordinate females. As our results did nut support alternative hypotheses to explain the observed bias in sex ratio among offspring at emergence, we conclude that the helper repayment hypothesis is the best candidate to explain the observed offspring sex ratio bias in Alpine marmots. By participating in social thermoregulation, subordinate males may repay part of the investment they received from their parents and thus become less costly to produce. We suggest that only subordinate males helped because they may gain direct fitness benefits, whereas subordinate females may only expect indirect fitness benefits from helping. Finally, the offspring sex ratio per individual parent was male biased, but mothers adjusted the size and the sex composition of their litters according to their phenotypic condition as expected from the Trivers-Willard hypothesis.