Genetic Structure in Cooperative Societies

理解社会行为的进化，特别是明显的合作，需要了解个体之间的遗传关系。进化理论证明了群体中亲属结构对合作和互惠等社会特征传播的潜在影响，这一理论已经得到了很好的发展。有人提出，即使是明显的利他行为（比如帮助他人抚养后代，而不是自己繁殖后代）也可能对捐赠者有益。当这种行为的潜在收益（实际繁殖者的繁殖能力被合作者与接受者的亲缘关系所加权）大于成本（独立繁殖可能产生的后代）时，这种解释就成立了。这种分析依赖于对合作者和幼崽之间基因相关性的准确评估，而这反过来又依赖于对谁生谁的精确了解。十年来，首席研究员研究了南美洲实行这种合作繁殖的几个种群（Campylorhynchus nuchalis， C.griseus和C. fasciatus）。这些鸟以大家庭的形式生活在永久的公共领土上，这种习惯在热带鸟类中很普遍。这些物种是上述进化思想的一个特别具有启发性的测试案例，合作有效地增加了可以产生的后代的数量。在多达11个繁殖季节的鹪鹩群中，有超过1600个个体可识别的个体。合作繁殖使繁殖成功率提高了5倍，因为单独的繁殖配对几乎总是失败。幼鸟通常在它们的出生地充当帮手，这意味着它们通常会帮助它们假定的父母生育兄弟姐妹。基于这一假设，合作有利于这些帮助者。我们对这项工作的扩展有两个目的。利用新开发的DNA指纹技术，pi将确定假定的繁殖者是否是这些家庭群体中唯一繁殖的鸟类，以及假定的非繁殖帮助者是否在帮助抚养兄弟姐妹。这种测试现在将基于遗传物质本身的确凿证据，而不是基于行为观察的错误推断。亲子关系在群体内部和群体之间的共享程度将被记录下来，分析模型和计算机模拟将量化亲子关系在社会群体中主要伴侣之外共享的潜在重要性。该项目将继续进行实地实验，研究竞争繁殖位置和群体防御捕食者的过程，这是群体繁殖优势的可疑机制。

Understanding the evolution of social behavior, especially apparent cooperation, requires knowledge of genetic relatedness among individuals. Evolutionary theory demonstrating the potential effects of kin-structure in populations on the spread od social traits like cooperation and reciprocity has been well developed. It is proposed that even apparently altruistic acts (like helping others to rear young rather than reproducing oneself) can be beneficial to the donor. This explanation holds when the potential benefits of such behavior (the enhancement of reproduction of the actual breeders weighted by the relatedness of the cooperator to recipients) more than balance the costs (young that could have produced in an independent breeding attempt). This analysis depends on accurate assessment of genetic relatedness between cooperator and young produced, which in turn depends on precise knowledge of exactly who begat whom. For ten years the principal investigator have studied several populations of wrens (Campylorhynchus nuchalis, C.griseus, and C. fasciatus) the practice such cooperative breeding in South America. These birds live in extended family groups on permanaent communal territories, a habit that is widespread among tropical birds. These species are an especially revealing test case of the above evolutionary ideas cooperation so effectively increases the number of young that can be produced. Pedigrees are available for as many as 11 breeding seasons in groups of wrens involving a total of more than 1600 individually recognizable individuals. Cooperation in breeding enhances reproductive success five-fold, as unaided breeding pairs almost always fail. Young birds usually remain as helpers on their natal territories, meaning they are usually helping their presumed parents produce siblings. Based on this assumption, cooperation benefits these helpers. Our extension of this work has two aims. Using newly- developed DNA fingerprinting techniques, the PIs will establish whether the presumed breeders are the only birds reproducing in these family groups, and whether putative nonbreeding helpers are aiding in rearing siblings. This test will now be based on conclusive evidence from the genetic material itself rather than on fallible inferences based on behavioral observation. The extent to which parentage is shared within and between groups will be documented, and analytical models and computer simulations will quantify the potential importance of parentage shared beyond a principal pair in social groups. The project will continue field experiments examining the processes of competition for productive breeding positions and group defense against predators, the suspected mechanism of the advantage of breeding in a group.