Tsutsui N D, Case T J
Section of Ecology, Behavior, and Evolution, University of California-San Diego, La Jolla 92093-0116, USA.
Evolution. 2001 May;55(5):976-85. doi: 10.1554/0014-3820(2001)055[0976:pgacso]2.0.co;2.
Introduced species often possess low levels of genetic diversity relative to source populations as a consequence of the small population sizes associated with founder events. Additionally, native and introduced populations of the same species can possess divergent genetic structuring at both large and small geographic scales. Thus, genetic systems that have evolved in the context of high diversity may function quite differently in genetically homogeneous introduced populations. Here we conduct a genetic analysis of native and introduced populations of the Argentine ant (Linepithema humile) in which we show that the population-level changes that have occurred during introduction have produced marked changes in the social structure of this species. Native populations of the Argentine ant are characterized by a pattern of genetic isolation by distance, whereas this pattern is absent in introduced populations. These differences appear to arise both from the effects of recent range expansion in the introduced range as well as from differences in gene flow within each range. Relatedness within nests and colonies is lower in the introduced range than in the native range as a consequence of the widespread genetic similarity that typifies introduced populations. In contrast, nestmates and colony-mates in the native range are more closely related, and local genetic differentiation is evident. Our results shed light on the problem posed for kin selection theory by the low levels of relatedness that are characteristic of many unicolonial species and suggest that the loss of genetic variation may be a common mechanism for the transition to a unicolonial colony structure.
由于与奠基者事件相关的种群规模较小，引入物种相对于源种群往往具有较低水平的遗传多样性。此外，同一物种的本地种群和引入种群在大地理尺度和小地理尺度上都可能具有不同的遗传结构。因此，在高多样性背景下进化的遗传系统在遗传同质的引入种群中可能具有截然不同的功能。在此，我们对阿根廷蚁（Linepithema humile）的本地种群和引入种群进行了遗传分析，结果表明，引入过程中发生的种群水平变化已使该物种的社会结构产生了显著变化。阿根廷蚁的本地种群具有按距离遗传隔离的模式，而引入种群中则不存在这种模式。这些差异似乎既源于引入范围内近期范围扩张的影响，也源于每个范围内基因流动的差异。由于引入种群典型的广泛遗传相似性，引入范围内巢穴和群体内的亲缘关系低于本地范围。相比之下，本地范围内的巢伴和群体成员关系更为密切，且存在明显的局部遗传分化。我们的研究结果揭示了许多单巢型物种所特有的低亲缘关系水平给亲缘选择理论带来的问题，并表明遗传变异的丧失可能是向单巢型群体结构转变的常见机制。
