Lin J E, Hard J J, Naish K A, Peterson D, Hilborn R, Hauser L
School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, USA.
Conservation Biology Division, Northwest Fisheries Science Center, National Marine Fisheries Service, NOAA, Seattle, WA, USA.
Heredity (Edinb). 2016 May;116(5):447-57. doi: 10.1038/hdy.2016.3. Epub 2016 Feb 10.
Predation can affect both phenotypic variation and population productivity in the wild, but quantifying evolutionary and demographic effects of predation in natural environments is challenging. The aim of this study was to estimate selection differentials and coefficients associated with brown bear (Ursus arctos) predation in wild sockeye salmon (Oncorhynchus nerka) populations spawning in pristine habitat that is often subject to intense predation pressure. Using reconstructed genetic pedigrees, individual reproductive success (RS) was estimated in two sockeye salmon populations for two consecutive brood years with very different predation intensities across brood years. Phenotypic data on individual adult body length, body depth, stream entry timing and reproductive lifespan were used to calculate selection coefficients based on RS, and genetic variance components were estimated using animal models. Bears consistently killed larger and more recently arrived adults, although selection differentials were small. In both populations, mean RS was higher in the brood year experiencing lower predation intensity. Selection coefficients were similar across brood years with different levels of predation, often indicating stabilizing selection on reproductive lifespan as well as directional selection for longer reproductive lifespan. Despite these selection pressures, genetic covariation of morphology, phenology and lifespan appears to have maintained variation in spawner body size and stream entry timing in both populations. Our results therefore suggest considerable demographic but limited evolutionary effects of bear predation in the two study populations.
捕食会影响野生动物的表型变异和种群生产力，但在自然环境中量化捕食的进化和人口统计学影响具有挑战性。本研究的目的是估计在原始栖息地产卵且经常面临强烈捕食压力的野生红大马哈鱼（Oncorhynchus nerka）种群中，与棕熊（Ursus arctos）捕食相关的选择差异和系数。利用重建的遗传谱系，在连续两个繁殖年份对两个红大马哈鱼种群的个体繁殖成功率（RS）进行了估计，这两个繁殖年份的捕食强度差异很大。利用成年个体的体长、体深、进入溪流时间和繁殖寿命的表型数据，根据RS计算选择系数，并使用动物模型估计遗传方差分量。熊一直捕杀体型较大且刚到达的成年个体，尽管选择差异很小。在两个种群中，捕食强度较低的繁殖年份的平均RS较高。在捕食水平不同的繁殖年份，选择系数相似，这通常表明对繁殖寿命的稳定选择以及对更长繁殖寿命的定向选择。尽管存在这些选择压力，但形态、物候和寿命的遗传协方差似乎在两个种群中都维持了产卵个体大小和进入溪流时间的变异。因此，我们的结果表明，在这两个研究种群中，熊捕食对种群数量有相当大的影响，但对进化的影响有限。
