Hendry Andrew P, Huber Sarah K, De León Luis F, Herrel Anthony, Podos Jeffrey
Department of Biology and Redpath Museum, McGill University, Montreal, Quebec, Canada H3A 2K6.
Proc Biol Sci. 2009 Feb 22;276(1657):753-9. doi: 10.1098/rspb.2008.1321.
A key part of the ecological theory of adaptive radiation is disruptive selection during periods of sympatry. Some insight into this process might be gained by studying populations that are bimodal for dual-context traits, i.e. those showing adaptive divergence and also contributing to reproductive isolation. A population meeting these criteria is the medium ground finch (Geospiza fortis) of El Garrapatero, Santa Cruz Island, Galápagos. We examined patterns of selection in this population by relating individual beak sizes to interannual recaptures during a prolonged drought. Supporting the theory, disruptive selection was strong between the two beak size modes. We also found some evidence of selection against individuals with the largest and smallest beak sizes, perhaps owing to competition with other species or to gaps in the underlying resource distribution. Selection may thus simultaneously maintain the current bimodality while also constraining further divergence. Spatial and temporal variation in G. fortis bimodality suggests a dynamic tug of war among factors such as selection and assortative mating, which may alternatively promote or constrain divergence during adaptive radiation.
适应性辐射生态理论的一个关键部分是同域期的歧化选择。通过研究具有双背景特征的双峰种群，即那些表现出适应性分化并导致生殖隔离的种群，可能会对这一过程有一些了解。满足这些标准的一个种群是加拉帕戈斯群岛圣克鲁斯岛埃尔加拉帕特罗的中型地雀（Geospiza fortis）。我们通过将个体喙大小与长期干旱期间的年度再捕获情况相关联，研究了该种群的选择模式。支持该理论的是，在两种喙大小模式之间歧化选择很强。我们还发现了一些针对喙最大和最小个体的选择证据，这可能是由于与其他物种的竞争或潜在资源分布的缺口。因此，选择可能同时维持当前的双峰性，同时也限制进一步的分化。中型地雀双峰性的空间和时间变化表明，在选择和选型交配等因素之间存在动态的拔河比赛，这在适应性辐射期间可能交替促进或限制分化。
