Peterson Merrill A, Denno Robert F
Department of Entomology, University of Maryland, College Park, Maryland, 20742.
Evolution. 1997 Aug;51(4):1189-1206. doi: 10.1111/j.1558-5646.1997.tb03967.x.
The hypothesis that levels of gene flow among populations are correlated with dispersal ability has typically been tested by comparing gene flow among species that differ in dispersal abilities, an approach that potentially confounds dispersal ability with other species-specific differences. In this study, we take advantage of geographic variation in the dispersal strategies of two wing-dimorphic planthopper species, Prokelisia marginata and P. dolus, to examine for the first time whether levels of gene flow among populations are correlated with intraspecific variation in dispersal ability. We found that in both of these coastal salt marsh-inhabiting species, population-genetic subdivision, as assessed using allozyme electrophoresis, parallels geographic variation in the proportion of flight-capable adults (macropters) in a population; in regions where levels of macroptery are high, population genetic subdivision is less than in regions where levels of macroptery are low. We found no evidence that geographic variation in dispersal capability influences the degree to which gene flow declines with distance in either species. Thus, both species provided evidence that intraspecific variation in dispersal strategies influences the genetic structure of populations, and that this effect is manifested in population-genetic structure at the scale of large, coastal regions, rather than in genetic isolation by distance within a region. This conclusion was supported by interspecific comparisons revealing that: (1) population-genetic structure (G ) of the two Prokelisia species correlated negatively with the mean proportion of flight-capable adults within a region; and (2) there was no evidence that the degree of isolation by distance increased with decreasing dispersal capability. Populations of the relatively sedentary P. dolus clustered by geographic region (using Nei's distances), but this was not the case for the more mobile P. marginata. Furthermore, gene flow among the two major regions we surveyed (Atlantic and Gulf Coasts) has been substantial in P. marginata, but relatively less in P. dolus. The results for P. marginata suggest that differences in the dispersal strategies of Atlantic and Gulf Coast populations occur despite extensive gene flow. We argue that gene flow is biased from Atlantic to Gulf Coast populations, indicating that selection favoring a reduction in flight capability must be intense along the Gulf. Together, the results of this study provide the first rigorous evidence of a negative relationship within a species between dispersal ability and the genetic structure of populations. Furthermore, regional variation in dispersal ability is apparently maintained by selective differences that outweigh high levels of gene flow among regions.
种群间基因流动水平与扩散能力相关的假说，通常是通过比较扩散能力不同的物种间的基因流动来进行检验的，这种方法可能会将扩散能力与其他物种特异性差异混淆。在本研究中，我们利用了两种具翅二型的飞虱物种——缘纹真飞虱（Prokelisia marginata）和多尔真飞虱（P. dolus）扩散策略的地理变异，首次检验种群间基因流动水平是否与扩散能力的种内变异相关。我们发现，在这两种栖息于沿海盐沼的物种中，使用等位酶电泳评估的种群遗传细分与种群中具飞行能力的成虫（长翅型）比例的地理变异平行；在长翅型比例高的地区，种群遗传细分程度低于长翅型比例低的地区。我们没有发现证据表明扩散能力的地理变异会影响这两个物种中任一物种基因流动随距离下降的程度。因此，这两个物种都提供了证据，表明扩散策略的种内变异会影响种群的遗传结构，并且这种影响在大型沿海区域尺度的种群遗传结构中体现，而非在区域内的距离隔离遗传中体现。种间比较支持了这一结论，表明：（1）两种真飞虱物种的种群遗传结构（G）与区域内具飞行能力成虫的平均比例呈负相关；（2）没有证据表明距离隔离程度会随着扩散能力的降低而增加。相对定居的多尔真飞虱种群按地理区域聚类（使用内氏距离），但更具移动性的缘纹真飞虱并非如此。此外，在我们调查的两个主要区域（大西洋海岸和墨西哥湾海岸）之间，缘纹真飞虱的基因流动很大，而多尔真飞虱相对较小。缘纹真飞虱的结果表明，尽管基因流动广泛，但大西洋海岸和墨西哥湾海岸种群的扩散策略仍存在差异。我们认为基因流动偏向于从大西洋海岸种群流向墨西哥湾海岸种群，这表明沿墨西哥湾有利于飞行能力降低的选择一定很强烈。总之，本研究结果首次提供了严格证据，证明一个物种内扩散能力与种群遗传结构之间存在负相关关系。此外，扩散能力的区域变异显然是由选择性差异维持的，这种差异超过了区域间高水平的基因流动。
