The ecological causes and consequences of hard and soft selection.

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.

Evaluating the outcomes of genetic rescue attempts.

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.

Predation risk drives aposematic signal conformity.

Contrary to expectations regarding efficient predator education mediated by lack of ambiguity and enhanced prey recognition, aposematic signals often show considerable intraspecific variability. For example, some striped skunks (Mephitis mephitis) are almost entirely white, others have black-and-white stripes of equivalent thicknesses, yet others are mostly black. We tested the ecological correlates of this variation in patterning using 749 museum skins collected across North America. Skunks had longer white-black borders and more bilaterally symmetrical stripes in areas with a greater number of potential predator species, and this effect was more marked for mammalian than avian predators, the latter of which may be less deterred by noxious defenses. Skunks from locations with greater predator diversity were less variable in the extent of whiteness on their dorsa and less variable in the length of their white-black borders, suggesting strong selection from predators leads to greater conformity in stripe patterns, even at the same location, but weak selection from predators leads to relaxed selection on pattern conformity. Skunks exhibited greater areas of black pelage in areas of greater humidity conforming to Gloger's rule. Our results indicate that relaxed predation pressure is key to warning signal variation in this iconic species, whereas stronger pressure leads to signal conformity and stronger signals.

Climate change and expanding invasive species drive widespread declines of native trout in the northern Rocky Mountains, USA.

Climate change and invasive species are major threats to native biodiversity, but few empirical studies have examined their combined effects at large spatial and temporal scales. Using 21,917 surveys collected over 30 years, we quantified the impacts of climate change on the past and future distributions of five interacting native and invasive trout species throughout the northern Rocky Mountains, USA. We found that the occupancy of native bull trout and cutthroat trout declined by 18 and 6%, respectively (1993­2018), and was predicted to decrease by an additional 39 and 16% by 2080. However, reasons for these occupancy reductions markedly differed among species: Climate-driven increases in water temperature and decreases in summer flow likely caused declines of bull trout, while climate-induced expansion of invasive species largely drove declines of cutthroat trout. Our results demonstrate that climate change can affect ecologically similar, co-occurring native species through distinct pathways, necessitating species-specific management actions.

The Exciting Potential and Remaining Uncertainties of Genetic Rescue.

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.

Environmental DNA for the enumeration and management of Pacific salmon.

Pacific salmon are a keystone resource in Alaska, generating annual revenues of well over ~US$500 million/year. Due to their anadromous life history, adult spawners distribute amongst thousands of streams, posing a huge management challenge. Currently, spawners are enumerated at just a few streams because of reliance on human counters and, rarely, sonar. The ability to detect organisms by shed tissue (environmental DNA, eDNA) promises a more efficient counting method. However, although eDNA correlates generally with local fish abundances, we do not know if eDNA can accurately enumerate salmon. Here we show that daily, and near-daily, flow-corrected eDNA rate closely tracks daily numbers of returning sockeye and coho spawners and outmigrating sockeye smolts. eDNA thus promises accurate and efficient enumeration, but to deliver the most robust numbers will need higher-resolution stream-flow data, at-least-daily sampling, and a focus on species with simple life histories, since shedding rate varies amongst jacks, juveniles, and adults.