Origin and evolution of Xerinae
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摘要: 归纳总结了地松鼠亚科Xerinae的起源和演化研究进展。现生地松鼠种类繁多、地理广布是由陆桥协助祖先类群扩散和生境变化导致祖先类群发生适应性演化共同作用的结果。化石和分子证据都表明地松鼠起源于早渐新世的欧亚大陆。地松鼠起源后很快分化出3支:第1支在19 Ma左右,即非洲欧亚陆桥第1次连接时扩散到非洲,在缺乏树栖松鼠竞争的情况下演化成现生的非洲树松鼠族Protoxerini;第2支在欧亚大陆向地栖生活演化的同时,部分类群在14 Ma左右扩散到非洲,并演化出非洲地松鼠族Xerini的Xerus和Atlantoxerus;第3支是旱獭族Marmotini的祖先,在欧亚大陆演化出岩松鼠属Sciurotamias的同时,于中渐新世通过白令陆桥扩散到北美,并在北美草原化的大背景下演化出花鼠属Tamias,黄鼠属Spermophilus,旱獭属Marmota,土拨鼠属Cynomys等。花鼠属、黄鼠属和旱獭属于中新世扩散回欧亚大陆,其中黄鼠属和旱獭属在欧亚大陆发生适应性演化。伴随生境变化而发生形态、行为等适应性演化,是地松鼠繁盛的重要原因。演化过程中,旱獭属、土拨鼠属、黄鼠属等地栖型松鼠的体型显著增大,尾巴显著变短,而半地栖型和树栖型的体型瘦长,尾巴变长。图2参53Abstract: The origin and evolution of Xerinae, a subfamily of squirrels, were chronicled revealing that their high biodiversity and wide distribution were due to the Africa-Eurasia Land Bridge and the Bering Land Bridge which facilitated dispersal and adaptive radiation. Both fossil and molecular evidence showed that Xerinae originated in Eurasia around the early-Oligocene epoch and soon evolved into three clades. Clade 1 dispersed to Africa via the Africa-Eurasia Land Bridge when it was first formed about 19 million years (Ma) ago. Since there was no competition from tree squirrels, Clade 1 gradually evolved into the Protoxerini. Clade 2 dispersed to Africa with the second formation of the Africa-Eurasia Land Bridge about 14 Ma evolving into Atlantoxerus and Xerus. Clade 3 was the ancestor of the Marmotini tribe; it evolved into Sciurotamias in Eurasia and simultaneously dispersed to North America via the Bering Land Bridge around the mid-Oligocene epoch. Following emergence of grass-dominated ecosystems in North America, this clade evolved into Tamias, Spermophilus, Marmota, and Cynomys. Tamias, Spermophilus, and Marmota re-occupied Eurasia in the Miocene period, and then Spermophilus and Marmota underwent their adaptive radiation in Eurasia. Xerinae thrived mainly because of morphological and behavioral variations that aided in adaptation to environmental change. During this course of evolution, ground dwellers like Marmota, Cynomys, and Spermophilus developed larger bodies with shorter tails; whereas, forest dwellers maintained slim bodies with relatively longer tails. [Ch, 2 fig. 53 ref.]
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.2015.05.021
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