Background Analysis of morphological variation in archipelagos has been essential to understand the evolution of terrestrial vertebrates. In particular, these natural scenarios allow to assess morphological changes experienced by insular fauna compared to their mainland counterparts. In mammals, morphological changes of insular forms have been observed in size and shape of body and cranial traits. The southern Patagonia of Chile represents a unique scenario to analyze morphological variation in two of the most widely distributed small rodents along western southern South America: Abrothrix olivacea and Oligoryzomys longicaudatus . Methods We applied linear and three-dimensional geometric morphometric tools to analyze the variation in cranial morphology of A. olivacea ( N = 80) and O. longicaudatus ( N = 49) . Sampled localities were distributed in the mainland and islands of the Fuegian archipelago in Chilean Patagonia. Standard multivariate methods, as Principal Components Analysis, and Logistic Regression models were carried out to evaluate differences in size and shape of crania. Results We detected higher levels of morphological variation in the crania of A. olivacea if compared to O. longicaudatus . The variation was associated to cranial size instead of shape. We observed significant differences between insular and mainland individuals in A. olivacea , being the cranium size of this species significantly bigger on islands. Indeed, specimens of A. olivacea from “Isla Wellington”, exhibited the higher increment in cranium size compared to any other mainland and insular site sampled for this species . In contrast, insular and mainland forms of O. longicaudatus did not show significant differences in cranial morphology. Conclusions We suggest that the patterns of morphological variation observed in these two small rodents along Patagonia, could be explained in terms of the historical biogeography of the region, and the different ecological features of the studied species.

中文翻译：

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智利南部巴塔哥尼亚大陆和 Fuegian 群岛的两种 Sigmodontine 啮齿动物的形态变异

群岛形态变异的背景分析对于了解陆生脊椎动物的进化至关重要。特别是，这些自然场景允许评估岛屿动物群与其大陆同行相比所经历的形态变化。在哺乳动物中，已在身体的大小和形状以及颅骨特征方面观察到岛状体的形态学变化。智利巴塔哥尼亚南部代表了一种独特的场景，可以分析南美洲南部西部分布最广泛的两种小型啮齿动物的形态变异：Abrothrix olivacea 和 Oligoryzomys longicaudatus。方法我们应用线性和三维几何形态测量工具来分析 A. olivacea ( N = 80) 和 O. longicaudatus ( N = 49) 颅骨形态的变化。采样地点分布在智利巴塔哥尼亚的 Fuegian 群岛的大陆和岛屿。执行标准多变量方法，如主成分分析和逻辑回归模型，以评估颅骨大小和形状的差异。结果与 O. longicaudatus 相比，我们在 A. olivacea 的颅骨中检测到更高水平的形态变异。这种变化与颅骨大小而不是形状有关。我们在 A. olivacea 中观察到岛屿和大陆个体之间的显着差异，因为该物种的颅骨大小在岛屿上明显更大。实际上，与为该物种采样的任何其他大陆和岛屿地点相比，来自“惠灵顿岛”的 A. olivacea 标本的颅骨大小增加了更高。相比之下，岛屿和大陆形式的 O. longicaudatus 在颅骨形态上没有表现出显着差异。结论我们认为，在巴塔哥尼亚沿岸的这两种小型啮齿动物中观察到的形态变异模式可以从该地区的历史生物地理和所研究物种的不同生态特征方面进行解释。