Hatfield Todd, Schluter Dolph
Zoology Department and Centre for Biodiversity, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada.
Evolution. 1999 Jun;53(3):866-873. doi: 10.1111/j.1558-5646.1999.tb05380.x.
"Ecological" speciation occurs when reproductive isolation evolves as a consequence of divergent selection between populations exploiting different resources or environments. We tested this hypothesis of speciation in a young stickleback species pair by measuring the direct contribution of ecological selection pressures to hybrid fitness. The two species (limnetic and benthic) are strongly differentiated morphologically and ecologically, whereas hybrids are intermediate. Fitness of hybrids is high in the laboratory, especially F and F hybrids (backcrosses may show some breakdown). We transplanted F hybrids to enclosures in the two main habitats in the wild to test whether the distribution of resources available in the environment generates a hybrid disadvantage not detectable in the laboratory. Hybrids grew more slowly than limnetics in the open water habitat and more slowly than benthics in the littoral zone. Growth of F hybrids was inferior to the average of the parent species across both habitats, albeit not significantly. The contrast between laboratory and field results supports the hypothesis that mechanisms of F hybrid fitness in the wild are primarily ecological and do not result from intrinsic genetic incompatibilities. Direct selection on hybrids contributes to the maintenance of sympatric stickleback species and may have played an important role in their origin.
“生态”物种形成发生在生殖隔离因利用不同资源或环境的种群间的趋异选择而进化时。我们通过测量生态选择压力对杂种适合度的直接影响，在一个年轻的棘鱼物种对中检验了这种物种形成假说。这两个物种（湖沼型和底栖型）在形态和生态上有很大差异，而杂种则是中间类型。杂种在实验室中的适合度很高，尤其是F1和F2杂种（回交可能会出现一些衰退）。我们将F1杂种移植到野外的两个主要栖息地的围栏中，以测试环境中可用资源的分布是否会产生在实验室中无法检测到的杂种劣势。在开阔水域栖息地，杂种的生长速度比湖沼型棘鱼慢，在沿岸带比底栖型棘鱼慢。在这两个栖息地中，F1杂种的生长都不如亲本物种的平均水平，尽管差异不显著。实验室和野外结果的对比支持了这样一种假说，即野生环境中F1杂种适合度的机制主要是生态性的，而非源于内在的遗传不相容性。对杂种的直接选择有助于同域棘鱼物种的维持，并且可能在它们的起源过程中发挥了重要作用。
