Partial migration strategies, in which some individuals migrate but others do not, are widely observed in populations of migratory animals. Such patterns could arise via variation in migratory behaviors made by individual animals, via genetic variation in migratory predisposition, or simply by variation in migration opportunities mediated by environmental conditions. Here we use spatiotemporal variation in partial migration across populations of an amphidromous Hawaiian goby to test whether stream or ocean conditions favor completing its life cycle entirely within freshwater streams rather than undergoing an oceanic larval migration. Across 35 watersheds, microchemical analysis of otoliths revealed that most adult Awaous stamineus were freshwater residents (62% of n = 316 in 2009, 83% of n = 274 in 2011), but we found considerable variation among watersheds. We then tested the hypothesis that the prevalence of freshwater residency increases with the stability of stream flows and decreases with the availability of dispersal pathways arising from ocean hydrodynamics. We found that streams with low variation of daily discharge were home to a higher incidence of freshwater residents in each survey year. The magnitude of the shift in freshwater residency between survey years was positively associated with predicted interannual variability in the success of larval settlement in streams on each island based on passive drift in ocean currents. We built on these findings by developing a theoretical model of goby life history to further evaluate whether mediation of migration outcomes by stream and ocean hydrodynamics could be sufficient to explain the range of partial migration frequency observed across populations. The model illustrates that the proportion of larvae entering the ocean and differential survival of freshwater-resident versus ocean-going larvae are plausible mechanisms for range-wide shifts in migration strategies. Thus, we propose that hydrologic variation in both ocean and stream environments contributes to spatiotemporal variation in the prevalence of migration phenotypes in A. stamineus. Our empirical and theoretical results suggest that the capacity for partial migration could enhance the persistence of metapopulations of diadromous fish when confronted with variable ocean and stream conditions.

中文翻译：

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溪流和海洋流体动力学调节两栖夏威夷虾虎鱼的部分迁徙策略

在迁徙动物种群中广泛观察到部分迁移策略，其中一些个体迁移但其他个体不迁移。这种模式可能是由于个体动物迁徙行为的变化、迁徙倾向的遗传变异或仅仅是环境条件介导的迁徙机会的变化而产生的。在这里，我们使用两栖夏威夷虾虎鱼种群部分迁移的时空变化来测试溪流或海洋条件是否有利于完全在淡水溪流内完成其生命周期，而不是进行海洋幼体迁移。在 35 个流域中，耳石的微化学分析表明，大多数成年Awaous stamineus是淡水居民（62% 的n= 2009 年 316 人，占n 的 83% = 274 in 2011)，但我们发现流域之间存在相当大的差异。然后，我们检验了以下假设：淡水居民的普遍性随着溪流的稳定性而增加，并随着海洋流体动力学产生的扩散途径的可用性而减少。我们发现，在每个调查年度，每日流量变化较小的溪流是淡水居民发生率较高的地方。基于洋流的被动漂移，调查年份之间淡水居住地变化的幅度与预测的幼虫在每个岛屿的溪流中成功定居的年际变化呈正相关。我们在这些发现的基础上建立了虾虎鱼生活史的理论模型，以进一步评估溪流和海洋流体动力学对迁徙结果的调节是否足以解释在种群中观察到的部分迁徙频率范围。该模型表明，进入海洋的幼虫比例以及淡水幼虫与远洋幼虫的生存差异是迁徙策略大范围转变的合理机制。因此，我们提出海洋和溪流环境中的水文变化有助于迁移表型流行的时空变化 该模型表明，进入海洋的幼虫比例以及淡水幼虫与远洋幼虫的生存差异是迁徙策略大范围转变的合理机制。因此，我们提出海洋和溪流环境中的水文变化有助于迁移表型流行的时空变化 该模型表明，进入海洋的幼虫比例以及淡水幼虫与远洋幼虫的生存差异是迁徙策略大范围转变的合理机制。因此，我们提出海洋和溪流环境中的水文变化有助于迁移表型流行的时空变化A. 雄蕊。我们的经验和理论结果表明，当面临多变的海洋和溪流条件时，部分迁移的能力可以增强溯河鱼类集合种群的持久性。