School of Aquatic and Fishery Sciences, University of Washington, Seattle, 98105, USA.
BMC Evol Biol. 2012 Jul 17;12:116. doi: 10.1186/1471-2148-12-116.
A number of studies have measured selection in nature to understand how populations adapt to their environment; however, the temporal dynamics of selection are rarely investigated. The aim of this study was to assess the temporal variation in selection by comparing the mode, direction and strength of selection on fitness-related traits between two cohorts of coho salmon (Oncorhynchus kisutch). Specifically, we quantified individual reproductive success and examined selection on date of return and body length in a wild population at Big Beef Creek, Washington (USA).
Reproductive success and the mode, direction and strength of selection on date of return and body length differed between two cohorts sampled in 2006 and 2007. Adults of the first brood year had greater success over those of the second. In 2006, disruptive selection favored early and late returning individuals in 2-year-old males, and earlier returning 3-year-old males had higher fitness. No evidence of selection on date of return was detected in females. In 2007, selection on date of return was not observed in males of either age class, but stabilizing selection on date of return was observed in females. No selection on body length was detected in males of both age classes in 2006, and large size was associated with higher fitness in females. In 2007, selection favored larger size in 3-year-old males and intermediate size in females. Correlational selection between date of return and body length was observed only in 2-year-old males in 2006.
We found evidence of selection on body length and date of return to the spawning ground, both of which are important fitness-related traits in salmonid species, but this selection varied over time. Fluctuation in the mode, direction and strength of selection between two cohorts was likely to be due to factors such as changes in precipitation, occurrence of catastrophic events (flooding), the proportion of younger- versus older-maturing males, sex ratio and densities of spawners.
许多研究已经测量了自然界中的选择，以了解种群如何适应环境；然而，选择的时间动态很少被研究。本研究的目的是通过比较两个银鲑（Oncorhynchus kisutch）群体的适应性相关特征的选择模式、方向和强度，评估选择的时间变化。具体来说，我们量化了个体的繁殖成功率，并研究了在华盛顿比奇溪（美国）的一个野生种群中，返回日期和体长的选择。
2006 年和 2007 年两个群体的繁殖成功率以及返回日期和体长的选择模式、方向和强度不同。初产卵群体的成虫比二产卵群体的成虫有更高的成功率。2006 年，在 2 龄雄性中，干扰选择有利于早回和晚回的个体，而早回的 3 龄雄性有更高的适应性。在雌性中没有发现对返回日期的选择。2007 年，在两个年龄组的雄性中都没有观察到对返回日期的选择，但在雌性中观察到对返回日期的稳定选择。在 2006 年，两个年龄组的雄性都没有发现对体长的选择，而大型个体与雌性的更高适应性相关。2007 年，选择有利于 3 龄雄性的较大体型和雌性的中等体型。2006 年，只有在 2 龄雄性中观察到返回日期和体长之间的相关选择。
我们发现了对体长和返回产卵地日期的选择的证据，这两个都是鲑鱼科物种的重要适应性相关特征，但这种选择随时间而变化。两个群体之间选择模式、方向和强度的波动可能归因于降水变化、灾难性事件（洪水）的发生、年轻与成熟雄性的比例、性别比例和产卵者密度等因素。
