Studies on the Evolutionary Genetics of Pocket Gophers GenusThomomys

口袋地鼠是北美西部的地下啮齿动物，就其遗传和形态特征而言，是世界上最易变的哺乳动物之一。它们存在于从沙漠山谷到山顶的所有可用土壤类型中，分布在极其广泛的生态环境中。事实上，它们是其活动范围内许多地区的主要农业害虫，特别是在当地植被已被单一种植的紫花苜蓿或其他作物取代的地区。在过去的20年里，詹姆斯·巴顿研究了口袋地鼠种群之间的遗传分化的一些方面，如染色体变化和基因频率的变化。这些都为袋鼠种群进化分化的过程提供了线索，这种分化在种群中很容易观察到。目前的建议将主要针对袋鼠种群形态变化的各个方面，特别强调体型变化及其对生活史的各个方面的影响，如密度、产仔数、每年产仔数等。这项研究的重点是比较来自加州东部沙漠天然沙漠灌丛植被群落的袖珍地鼠与入侵最近开发的单一紫花苜蓿种植的袋鼠种群。迄今为止的观察表明，在短短十几年左右的时间里，紫花苜蓿种群的平均体型增加了两倍以上，并且与这些体型变化相关的生殖性能发生了重大变化。这些繁殖变化如此之大，以至于种植紫花苜蓿的农民实际上也在种植袖珍地鼠。首席调查员将通过一系列的移植实验，将动物从自然植被转移到紫花苜蓿地，通过观察两种生境中个体的生长速度，以及在共同的营养条件下饲养在两种生境中出生的幼崽，来研究这种大小差异的原因。通过这样做，将确定体型的增加只是反映了以紫花苜蓿为代表的饮食的根本变化，还是代表了自然选择导致的遗传结构的重大变化。这些研究将包括几个不同的天然和紫花苜蓿种群配对，并将通过蛋白质电泳和DNA序列分析等遗传技术来确定这些配对之间的关系。

Pocket gophers, subterranean rodents of western North America, are among the world's most variable mammals with respect to their genetic and morphological features. They occur in all available soil types from desert valleys to mountain tops, across an extremely wide range of ecological settings. They are, in fact, major agricultural pests in many areas of their range, particularly in areas where the native vegetation has been replaced by monocultures of alfalfa or other crops. Over the past 20 years, James Patton has studied aspects of the genetic differentiation among populations of pocket gophers in features such as chromosomal changes and shifts in gene frequencies. These have provided clues to the processes involved in the development of the enormous degree of evolutionary divergence that is readily observable among populations of pocket gophers. The current proposal will be directed primarily to aspects of morphological change among pocket gopher populations, with particular emphasis on body size variation and its influence on various aspects of life history, such as density, litter size, number of litters per year, and so forth. The focus of the study is on comparisons between populations of pocket gophers from natural desertscrub vegetation communities in the deserts of eastern California and those that have invaded recently developed monocultures of alfalfa. Observations to date show that in as few as a dozen years or so, the average body size in alfalfa populations increases over two-fold, and that there are major shifts in reproductive performances associated with these body size changes. These reproductive changes are of such magnitude that alfalfa farmers are, in fact, also farming pocket gophers. The principal investigator will investigate the causal basis of this size variation by a series of transplant experiments, shifting animals from natural vegetation to alfalfa fields, by observing growth rates of individuals in both habitats, and by rearing young, born in the laboratory to mothers caught in both habitat types, under a common nutritional regime. By so doing, it will be determined if the body size increase is merely a reflection of the radical change in diet represented by alfalfa, or whether it represents a major change in genetical constitution due to natural selection. These studies will incorporate several different paired natural and alfalfa populations, and the relationships among the pairs will be ascertained by genetic techniques, such as protein electrophoresis and DNA sequence analysis.