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Although human fragmentation of freshwater habitats is ubiquitous, the genetic consequences of isolation and a roadmap to address them are poorly documented for most fishes. This is unfortunate, because translocation for genetic rescue could help mitigate problems. We used genetic data (32 SNPs) from 203 populations of westslope cutthroat trout (Oncorhynchus clarkii lewisi) to (1) document the effect of fragmentation on genetic variation and population structure, (2) identify candidate populations for genetic rescue, and (3) quantify the potential benefits of strategic translocation efforts. Human-isolated populations had substantially lower genetic variation and elevated genetic differentiation, indicating that many populations are strongly influenced by random genetic drift. Based on simple criteria, 23 populations were candidates for genetic rescue, which represented a majority (51%) of suitable populations in one major region (Missouri drainage). Population genetic theory suggests that translocation of a small number of individuals (∼5 adults) from nearby populations could dramatically increase heterozygosity by up to 58% (average across populations). This effort provides a clear template for future conservation of westslope cutthroat trout, while simultaneously highlighting the potential need for similar efforts in many freshwater species.

Augmenting gene flow is a powerful tool for the conservation of small, isolated populations. However, genetic rescue attempts have largely been limited to populations at the brink of extinction, in part due to concerns over negative outcomes (e.g., outbreeding depression). Increasing habitat fragmentation may necessitate more proactive genetic management. Broader application of augmented gene flow will, in turn, require rigorous evaluation to increase confidence and identify pitfalls in this approach. To date, there has been no assessment of best monitoring practices for genetic rescue attempts. We used genomically explicit, individual-based simulations to examine the effectiveness of common approaches (i.e., tests for increases in fitness, migrant ancestry, heterozygosity, and abundance) for determining whether genetic rescue or outbreeding depression occurred. Statistical power to detect the effects of gene flow on fitness was high (≥0.8) when effect sizes were large, a finding consistent with those from previous studies on severely inbred populations. However, smaller effects of gene flow on fitness can appreciably affect persistence probability but current evaluation approaches fail to provide results from which reliable inferences can be drawn. The power of the metrics we examined to evaluate genetic rescue attempts depended on the time since gene flow and whether gene flow was beneficial or deleterious. Encouragingly, the use of multiple metrics provided nonredundant information and improved inference reliability, highlighting the importance of intensive monitoring efforts. Further development of best practices for evaluating genetic rescue attempts will be crucial for a responsible transition to increased use of translocations to decrease extinction risk.Evaluación de los Resultados de los Intentos de Rescate Genético Resumen El aumento del flujo génico es una herramienta poderosa para la conservación de poblaciones pequeñas y aisladas. Sin embargo, los intentos de rescate genético en su mayoría se han limitado a las poblaciones que se encuentran al borde de la extinción, en parte debido a la preocupación que existe por los resultados negativos (es decir, la depresión exogámica). La creciente fragmentación del hábitat puede requerir un manejo genético más proactivo. La aplicación más extensa del flujo génico aumentado requerirá a su vez una evaluación rigurosa para incrementar la confianza e identificar las dificultades de esta estrategia. A la fecha, no ha habido una evaluación de las mejores prácticas de monitoreo para los intentos de rescate genético. Usamos simulaciones explícitas basadas en individuos para examinar la efectividad de las estrategias comunes (es decir, análisis del incremento en adaptabilidad, ascendencia migratoria, heterocigosidad y abundancia) para determinar si ocurrió el rescate genético o la depresión exogámica. El poder estadístico para detectar los efectos del flujo génico sobre la adaptabilidad fue elevado (≥0.8) cuando el tamaño de los efectos fue grande, un hallazgo consistente con aquellos realizados en estudios previos sobre poblaciones con una endogamia severa. Sin embargo, los efectos menores del flujo génico sobre la adaptabilidad pueden afectar de manera apreciable la probabilidad de persistencia, pero las estrategias actuales de evaluación no proporcionan resultados de los cuales se puedan hacer inferencias confiables. El poder de las medidas que examinamos para evaluar los intentos de rescate genético dependió del tiempo desde que inició el flujo génico y de si el flujo génico fue benéfico o perjudicial. De manera alentadora, el uso de múltiples medidas proporcionó información no redundante y mejoró la confiabilidad de la inferencia, resaltando así la importancia de los esfuerzos intensivos de monitoreo. El futuro desarrollo de mejores prácticas para la evaluación de los intentos de rescate genético será de suma importancia para la transición responsable hacia el mayor uso de reubicaciones para reducir el riesgo de extinción.扩大基因流是保护孤立小种群的有力工具。然而, 遗传拯救的尝试很大程度上局限于濒临灭绝的种群, 部分原因是担忧出现负面结果 (如远交衰退) 。目前, 栖息地的日益破碎化正在迫使人们采取更积极的遗传管理措施。增加基因流的广泛应用也需要严格的评估, 以增强对这种方法的信心并识别其中的缺陷。迄今为止, 还没有研究对遗传拯救尝试的最佳监测实践进行评估。本研究使用基于个体的基因组显式模拟检验了常见方法的有效性(检验适合度是否增加、迁徙遗传祖先、杂合度和丰度), 以确定是否实现了遗传拯救或发生了远交衰退。当效应量较大时, 检测基因流对适合度影响的统计功效很高 (≥0.8), 这一发现与之前对严重近交群体的研究结果一致。然而, 基因流对适合度较小的影响也可以显著影响种群续存的概率, 但目前的评估方法无法提供能够得出可靠推论的结果。我们用来评估遗传拯救尝试的指标的功效取决于基因流发生的时间以及基因流产生了有益还是有害的影响。令人鼓舞的是, 使用多重指标可以提供非冗余信息并提高推断的可靠性, 这突出了加强监控工作的重要性。进一步发展评估遗传拯救尝试的最佳方法, 对于负责任地逐步增加迁地保护的使用以减少灭绝风险将是至关重要的。【翻译: 胡怡思; 审校: 聂永刚】.

Restoring gene flow into small, isolated populations can alleviate genetic load and decrease extinction risk (i.e., genetic rescue), yet gene flow is rarely augmented as a conservation strategy. Due to this discrepancy between opportunity and action, a recent call was made for widespread genetic rescue attempts. However, several aspects of augmenting gene flow are poorly understood, including the magnitude and duration of beneficial effects and when deleterious effects are likely to occur. We discuss the remaining uncertainties of genetic rescue in order to promote and direct future research and to hasten progress toward implementing this potentially powerful conservation strategy on a broader scale.

Interactions between natural selection and population dynamics are central to both evolutionary-ecology and biological responses to anthropogenic change. Natural selection is often thought to incur a demographic cost that, at least temporarily, reduces population growth. However, hard and soft selection clarify that the influence of natural selection on population dynamics depends on ecological context. Under hard selection, an individual's fitness is independent of the population's phenotypic composition, and substantial population declines can occur when phenotypes are mismatched with the environment. In contrast, under soft selection, an individual's fitness is influenced by its phenotype relative to other interacting conspecifics. Soft selection generally influences which, but not how many, individuals survive and reproduce, resulting in little effect on population growth. Despite these important differences, the distinction between hard and soft selection is rarely considered in ecology. Here, we review and synthesize literature on hard and soft selection, explore their ecological causes and implications and highlight their conservation relevance to climate change, inbreeding depression, outbreeding depression and harvest. Overall, these concepts emphasise that natural selection and evolution may often have negligible or counterintuitive effects on population growth-underappreciated outcomes that have major implications in a rapidly changing world.

Differential climate-induced shifts in phenology can create mismatches between predators and prey, but few studies have examined predator–prey mismatch across multiple life-history stages. We used long-term data from a warming stream with shifting salmonid migration timings to quantify intra-annual migration synchrony between predatory Dolly Varden (Salvelinus malma) and Pacific salmon prey and examined how predator–prey synchrony has been influenced by climate change. We demonstrate that Dolly Varden have become increasingly mismatched with spring downstream migrations of abundant pink salmon (Oncorhynchus gorbuscha) juveniles. However, Dolly Varden have remained matched with fall upstream migrations of spawning Pacific salmon, including coho (Oncorhynchus kisutch), sockeye (Oncorhynchus nerka), and pink salmon. Downstream predator–prey migration synchrony decreased over time and with higher temperatures, particularly with pink salmon. In contrast, upstream migration synchrony was temporally stable and increased with rising temperatures. Differing trends in Dolly Varden predator–prey synchrony may be explained by the direct use of salmon to cue upstream migration, but not downstream migration. Overall, we show that climate change can have differing impacts on predator–prey synchrony across life-history stages.