Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2054;
Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907-2054.
Proc Natl Acad Sci U S A. 2018 Apr 24;115(17):4441-4446. doi: 10.1073/pnas.1801779115. Epub 2018 Apr 11.
The maintenance of diverse life history strategies within and among species remains a fundamental question in ecology and evolutionary biology. By using a near-complete 16-year pedigree of 12,579 winter-run steelhead () from the Hood River, Oregon, we examined the continued maintenance of two life history traits: the number of lifetime spawning events (semelparous vs. iteroparous) and age at first spawning (2-5 years). We found that repeat-spawning fish had more than 2.5 times the lifetime reproductive success of single-spawning fish. However, first-time repeat-spawning fish had significantly lower reproductive success than single-spawning fish of the same age, suggesting that repeat-spawning fish forego early reproduction to devote additional energy to continued survival. For single-spawning fish, we also found evidence for a fitness trade-off for age at spawning: older, larger males had higher reproductive success than younger, smaller males. For females, in contrast, we found that 3-year-old fish had the highest mean lifetime reproductive success despite the observation that 4- and 5-year-old fish were both longer and heavier. This phenomenon was explained by negative frequency-dependent selection: as 4- and 5-year-old fish decreased in frequency on the spawning grounds, their lifetime reproductive success became greater than that of the 3-year-old fish. Using a combination of mathematical and individual-based models parameterized with our empirical estimates, we demonstrate that both fitness trade-offs and negative frequency-dependent selection observed in the empirical data can theoretically maintain the diverse life history strategies found in this population.
在物种内部和之间维持多样化的生活史策略仍然是生态学和进化生物学的一个基本问题。通过使用俄勒冈州胡德河的 12579 尾冬季洄游钢头鱼（Oncorhynchus mykiss）近 16 年的完整 pedigree，我们研究了两种生活史特征的持续维持：产卵次数（单次产卵与多次产卵）和首次产卵年龄（2-5 岁）。我们发现，多次产卵的鱼的终生繁殖成功率是单次产卵的鱼的 2.5 倍以上。然而，首次多次产卵的鱼的繁殖成功率明显低于同龄的单次产卵的鱼，这表明多次产卵的鱼放弃了早期繁殖，以将额外的能量用于持续生存。对于单次产卵的鱼，我们还发现了产卵年龄的适应度权衡的证据：年龄较大、体型较大的雄性比年龄较小、体型较小的雄性具有更高的繁殖成功率。对于雌性，相比之下，尽管我们观察到 4 岁和 5 岁的鱼在产卵场的频率降低，但我们发现 3 岁的鱼的终生平均繁殖成功率最高。这种现象可以用负频率依赖选择来解释：随着 4 岁和 5 岁的鱼在产卵场的频率降低，它们的终生繁殖成功率变得大于 3 岁的鱼。通过使用数学模型和基于个体的模型的组合，并以我们的经验估计作为参数，我们证明了在经验数据中观察到的适应度权衡和负频率依赖选择都可以从理论上维持该种群中多样化的生活史策略。
