Toward a Unifying Theory of Social Evolution: Testing Competing Models of Reproductive Skew in an Avian Cooperative Breeder

迈向社会进化的统一理论：在鸟类合作繁殖者中测试繁殖偏态的竞争模式。家庭（定义为多代遗传亲属的集合）是所有社会组织形式中最难以理解的。然而，因为它是我们人类的基本社会组织，它可以说是对我们来说最重要的理解。只有大约3%的鸟类和哺乳动物生活在以家庭为基础的社会中，其中只有少数得到了详细的研究。家庭的规模和形式各不相同。在鸟类和哺乳动物中最常见的形式是核心家庭，当成年的孩子和父母呆在一起，但只有父母繁殖时，就形成了核心家庭。大多数所谓的“合作繁殖者”都属于这一类，成年的儿子和女儿留在父母的巢穴或洞穴里做帮手。大家庭不太常见，但更有趣的是，当许多家庭成员共同生育时形成的大家庭。当一个家庭中的多对狗杂交时，结果不仅是父母和后代的杂交，而且是祖父母、叔叔和阿姨、侄女和侄子、表亲以及没有血缘关系的姻亲的杂交。直到最近，我们人类主要生活在由这种大家庭单位组成的群体中。大家庭和核心家庭的区别在于共同繁殖和垄断繁殖。数量迅速增长的进化模型，统称为生殖偏态理论，试图解释自然界中发现的生殖抑制的可变性。倾斜模型结合了少量因素（两个生态因素，一个遗传因素，一个社会因素）来预测1)稳定的家庭群体何时形成，2)稳定的家庭群体规模将是多少，以及3)如何在家庭成员之间共享繁殖。生殖偏差引起了行为生态学家和进化生物学家的极大兴趣，因为它将动物社会的许多主要特征与其生态、遗传和社会基础联系起来。由于这种广泛性，一些研究人员认为，偏态理论可能为观察社会进化提供了一个统一的框架。然而，该理论的发展速度远远超过了在该领域用真实动物对其假设和预测进行测试的速度。目前迫切需要对生活在家庭社会中的鸟类和哺乳动物的偏态理论进行详细的观察和实验研究。拟议中的研究将提供这样一种检验。研究物种是灰帽群居编织者（Pseudonigrita arnaudi），一种东非呼啸荆棘大草原的常见居民。之所以选择这个物种，是因为它既生活在扩展家庭中，也生活在核心家庭中，对它的行为和生态学的背景知识已经众所周知，而且它具有许多特征，使它在后勤上很容易收集数据和进行实验。已捕获了50多个家庭单位的研究种群，并对其进行了单独标记。已经开发出分子标记（微卫星位点），可以从遗传学角度确定家庭结构（例如，谁是谁的父亲或姨妈）。该研究项目将帮助培养许多肯尼亚专业人员使用现代行为研究方法。它还将结合几位高级研究人员的才能，他们的专业知识范围从行为的实地研究到社会组织的分子研究，再到社会进化的理论建模。因此，它构成了最近的倾斜模型对复杂脊椎动物社会适用性的第一个综合测试之一。研究结果将增强我们对以下方面的理解：1)有利于家庭群体进化的因素；2)大家庭发展的原因；3)家庭成员在相互合作和竞争互动中使用的行为（所谓的“家庭动态”）。反过来，这也应该为我们自己物种中有利于进化和维持大家庭的条件提供见解。

TOWARD A UNIFYING THEORY OF SOCIAL EVOLUTION: TESTING COMPETING MODELS OF REPRODUCTIVE SKEW IN AN AVIAN COOPERATIVE BREEDER.STEPHEN T. EMLENPROJECT SUMMARY (IN LAY TERMS)The family (defined as a multi-generation assemblage of genetic relatives) is among the least understood of all forms of social organization. Yet, because it is the basic social organization of our own species, it is arguably the most important for us to understand. Only about 3% of birds and mammals live in family-based societies, and only a few of these have been studied in detail.Families come in various sizes and forms. The most common form in both birds and mammals is the nuclear family, formed when grown young remain with their parents, but only the parents reproduce. Most so-called 'cooperative breeders' fit this category, with grown sons and daughters remaining as helpers at the nest or den of their parents. Less common, but of greater interest, is the extended family, formed when reproduction is shared among many family members. When multiple pairs within a single family breed, the result is a mixture not only of parents and offspring, but also of grandparents, uncles and aunts, nieces and nephews, and cousins as well as unrelated in-laws. Until very recently, we humans lived predominantly in groups comprised of such extended family units. The difference between extended and nuclear families is one of shared versus monopolized breeding. A rapidly growing number of evolutionary models, known collectively as reproductive skew theory, attempt to explain the variability of reproductive suppression found in nature. Skew models incorporate a small number of factors (two ecological, one genetic, and one social) to predict 1) when stable family groups will form, 2) what their stable size will be, and 3) how reproduction will be shared among family members.Reproductive skew they is generating considerable interest among behavioral ecologists and evolutionary biologists because it links many major features of animal societies to their ecological, genetic, and social underpinnings. Because of this breadth, some workers believe that skew theory may provide a unifying framework for viewing much of social evolution. However, the development of the theory has far outpaced the testing of its assumptions and predictions with real animals in the field. There is an urgent need for detailed observational and experimental studies of skew theory on birds and mammals that live in family-based societies.The proposed research will provide such a test. The study species is the Grey capped social weaver (Pseudonigrita arnaudi), a common inhabitant of the whistling thorn savanna of East Africa. This species was chosen because it lives in both extended and nuclear family units, background knowledge of its behavior and ecology is already well-known, and it possesses many features that make it logistically easy to collect data and perform experiments. A study population of over 50 family units has been captured and the birds individually marked. Molecular markers (microsatellite loci) have been developed that will allow genetic determination of family structures (e.g. who is the father, or aunt, of whom). The research program will help to train numerous Kenyan professionals in modern methods of behavioral research. It will also combine the talents of several senior investigators whose expertise ranges from field studies of behavior, to molecular studies of social organization, to theoretical modeling of social evolution. As such, it constitutes one of the first integrated tests of the applicability of recent skew models to a complex vertebrate society.The results should enhance our understanding of 1) the factors that favor the evolution of family groups, 2) the reasons why extended families develop when they do, and 3) the behaviors that family members use in their cooperative and competitive interactions with one another (so-called 'family dynamics'). This, in turn, should provide insights into the conditions that favored the evolution and maintenance of extended family groupings in our own species as well.