Hamon Troy R, Foote Chris J
School of Aquatic and Fisheries Sciences, University of Washington, Box 355020, Seattle, Washington 98195-5020, USA.
Evolution. 2005 May;59(5):1104-18.
Concurrent natural and sexual selection have been inferred from laboratory and comparative studies in a number of taxa, but are rarely measured in natural populations. Because the interaction of these two general categories of selection may be complex when they occur simultaneously, empirical evidence from natural populations would help us to understand this interaction and probably give us greater insight into each separate episode as well. In male sockeye salmon, sexual selection for larger body size has been indicated in both deep and shallow water habitats. However, in shallow habitats male sockeye are generally smaller and less deep-bodied than in deep habitats, a difference that has been ascribed to natural selection. We measured concurrent natural and sexual selection in two years on breeding male sockeye salmon with respect to body size, body shape, and time of arrival to the breeding grounds. Natural selection was variable in effect and sexual selection was variable in intensity in these two years. The patterns of selection also appear to be interdependent; areas where predation on spawning adults is not intense have yielded different patterns of sexual selection than those measured here. It appears that some of the body shape differences in sockeye salmon associated with different spawning habitats, which were previously attributed to selective mortality, may be a result of different patterns of sexual selection in the different habitats. Total selection resulting from the combination of both natural and sexual selection was less intense than either natural or sexual selection in most cases. Measurement of concurrent selection episodes in nature may help us to understand whether the pattern of differential sexual selection is common, and whether observed patterns of habitat-related differentiation may be due to differences in sexual selection.
在许多分类群中，通过实验室研究和比较研究已经推断出自然选择和性选择同时存在，但在自然种群中却很少进行测量。由于这两种选择在同时发生时相互作用可能很复杂，来自自然种群的实证证据将有助于我们理解这种相互作用，并且可能也会让我们对每一种单独的选择过程有更深入的了解。在雄性红大马哈鱼中，无论是在深水还是浅水栖息地，都已表明存在对更大体型的性选择。然而，在浅水区，雄性红大马哈鱼通常比深水区的体型更小、身体更深，这种差异被归因于自然选择。我们在两年时间里对繁殖期雄性红大马哈鱼的体型、身体形状和到达繁殖地的时间进行了自然选择和性选择同时存在情况的测量。在这两年中，自然选择的效果是可变的，性选择的强度也是可变的。选择模式似乎也是相互依存的；产卵成年鱼被捕食不强烈的区域所产生的性选择模式与我们在此测量的不同。似乎红大马哈鱼中与不同产卵栖息地相关的一些身体形状差异，以前被归因于选择性死亡，可能是不同栖息地中性选择模式不同的结果。在大多数情况下，自然选择和性选择共同作用产生的总选择强度比自然选择或性选择中的任何一种都要弱。在自然界中测量同时发生的选择过程可能有助于我们理解差异性选择模式是否普遍，以及观察到的与栖息地相关的分化模式是否可能是由于性选择的差异。
