Phylogenetic Systematics of South American Akodontine Rodents (Muridae: Sigmodontinae)

南美洲啮齿动物辐射的大鼠和小鼠(主要是地方性亚科Sigmodontinae)代表了一大批生物，从亚地下到水生到乔木，从亚马逊盆地的热带雨林到安第斯山脉最高海拔的普纳草原，它们的形态适应范围很广。这种适应性辐射由大约70个属组成，其中大多数通常被分为五个主要谱系之一。其中，阿科多尼斯人是最多样化和最古老的物种之一，现代形式的化石可以追溯到大约600万年前的阿根廷。尽管这一谱系的多样性得到了广泛的认可，但大多数分类群都鲜为人知和定义，其生物学的系统发育、生态和生活史方面要么完全未知，要么几乎一无所知。这种辐射主要局限于从北安第斯山脉到巴塔哥尼亚草原的草原生境，大约有15个属和大约50个物种。本研究将利用通过聚合酶链式反应技术从中年生物基因组中的几个基因获得的DNA序列来解决以下一组一般目标：(1)建立一个关于该复合体所有属和大多数物种之间的系统发育关系的假说；(2)使用居住在安第斯山脉陡峭东坡的特定物种作为样本，执行物种形成模型的文本，该模型是由于在强生境梯度上的分歧而产生的；以及(3)确定确定该组合中高度派生的类群的特定头骨构象是否共享一个接近的共同祖先，或者这种类型的头骨结构是否在不同的谱系中重复进化。这项研究的令人兴奋的方面是，由于可以从自然历史收藏中已经保存的干燥皮肤样本中提取和扩增DNA，现在已经灭绝或极其稀有的类群可以用前所未有的方式进行比较。例如，受关注的五个属，每个属都是从很少的标本中已知的，其中大多数只从非常偏远的地区采集过一次。因此，这是第一次以比较的方式检查所有现存分类群的组内关系的研究。

Rats and mice of the South American murid rodent radiation (the largely endemic subfamily Sigmodontinae) represent a very large array of organisms that range in morphologic adaptations from subfossorial to aquatic to arborel and in habitat from tropical rainforest of the Amazon Basin to puna grassland in the highest elevations of the Andes. This adaptive radiation comprises some 70 genera, most of which are commonly divided into one of five major lineages. Among these, the akodontines are among the most diverse and oldest, with fossils of modern forms extending back some 6 million years in Argentina. Despite the widely recognized diversification of this lineage, most taxa are both poorly known and defined, and phylogenetic, ecologic, and life history aspects of their biology are either totally unknown or only barely so. This is particularly true for the akodontine group, a radiation of some 15 genera and about 50 species largely confined to grassland habitats from the northern Andes to the Patagonian steppes. The present research will utilize DNA sequences, obtained from several genes within the mithochrondrial genome by the technique of the Polymerase Chain Reaction, to address the following set of general goals: (1) establish an hypothesis of phylogenetic relationships among all genera and most species of the complex; (2) perform a text of the model of species formation resulting from divergence across strong habitat gradients, using selected species inhabiting the steep eastern slope of the Andes as exemplars; and (3) determine whether or not particular cranial conformations that identify highly derived taxa within this assemblage share a close common ancestor or whether this type of cranial structure has evolved repeatedly in separate lineages. The exciting aspect of this research is that, since DNA can be extracted and amplified from dried skin specimens already preserved within natural history collections, now extinct or exceedingly rare taxa can be compared in ways never before available. Five of the genera of concern, for example, are each known form very few specimens, most of which only collected once from very remote areas. This is, therefore, the first study of relationships within the group to examine all extant taxa in a comparative way.