Rubenstein Dustin R, Shen Sheng-Feng
Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720, USA.
Am Nat. 2009 May;173(5):650-61. doi: 10.1086/597606.
Conflict over reproduction is an inherent part of group living. In many social vertebrates, conflict may be reflected as allostatic load, or the costs of social status and dominance rank, which may be quantified by measuring glucocorticoid stress hormones. Here, we develop the first quantitative model of allostatic load based on the tug-of-war model of reproductive skew to generate insights into the mechanisms underlying reproductive conflict in cooperative breeders and to determine whether glucocorticoids can be used to assess conflict levels in group-living vertebrates. It predicts that subordinates have higher allostatic loads than dominants under most conditions, but when body condition is lower in dominants than in subordinates, dominants experience higher allostatic load. Group structure is also important, as dominants generally have higher allostatic loads than subordinates when there is a large number of subordinates in the group, but this cost can be reduced by increasing the number of dominants, as in plural breeding societies. Using glucocorticoid data from cooperatively breeding superb starlings Lamprotornis superbus, we found empirical support for both predictions. Our model is useful for understanding how the costs of social status influence reproductive sharing, and it suggests that glucocorticoids can be used to examine reproductive conflict and cooperation in social species.
繁殖冲突是群居生活的一个固有组成部分。在许多社会性脊椎动物中，冲突可能表现为应激负荷，即社会地位和优势等级的代价，这可以通过测量糖皮质激素应激激素来量化。在这里，我们基于繁殖偏斜的拔河模型开发了第一个应激负荷定量模型，以深入了解合作繁殖者中繁殖冲突的潜在机制，并确定糖皮质激素是否可用于评估群居脊椎动物的冲突水平。该模型预测，在大多数情况下，从属个体的应激负荷高于优势个体，但当优势个体的身体状况低于从属个体时，优势个体的应激负荷会更高。群体结构也很重要，因为当群体中有大量从属个体时，优势个体的应激负荷通常高于从属个体，但在多元繁殖社会中，通过增加优势个体的数量可以降低这种代价。利用合作繁殖的华丽辉椋鸟的数据，我们为这两个预测都找到了实证支持。我们的模型有助于理解社会地位的代价如何影响繁殖共享，并且表明糖皮质激素可用于研究社会物种中的繁殖冲突与合作。
