Scottish Centre for Ecology & the Natural Environment, Institute of Biodiversity Animal Health and Comparative Medicine, University of Glasgow, Rowardennan, Glasgow, UK.
Faculty of Environmental Sciences and Natural Resource Management, The Norwegian University of Life Sciences, Ås, Norway.
J Fish Biol. 2022 Apr;100(4):860-867. doi: 10.1111/jfb.15024. Epub 2022 Mar 9.
There are strong signals that the selection forces favouring the expression of long-distance sea migration by Atlantic salmon (Salmo salar) are changing. Unlike many other behavioural traits, the costs of migration are incurred before any fitness benefits become apparent to the migrant. The expression of this behaviour has thus been shaped by selection forces over multiple generations and cannot respond to short interval (within a single generation) environmental change as many other behavioural traits can. Here we provide a framework to examine the evolutionary and ecological consequences of a sustained increase in migration cost. We argue that Atlantic salmon may have entered an evolutionary trap, where long-distance sea migration has become maladaptive because of shifting environmental conditions. We predict that if higher migration costs (affecting survivorship and ultimately fitness) persist, then shifting selection pressures will result in continuing declines in population size. We suggest, however, that in some populations there is demonstrable capacity for evolutionary rescue responses within the species which is to be found in the variation in the expression of migration. Under a scenario of low to moderate change in the selection forces that previously promoted migration, we argue that disruptive, sex-based selection would result in partial migration, where females retain sea migration but with anadromy loss predominantly in males. With more acute selection forces, anadromy may be strongly selected against, under these conditions both sexes may become freshwater resident. We suggest that as the migration costs appear to be higher in catchments with standing waters, then this outcome is more likely in such systems. We also speculate that as a result of the genetic structuring in this species, not all populations may have the capacity to respond adequately to change. The consequences of this for the species and its management are discussed.
有强烈的信号表明，支持大西洋鲑（Salmo salar）进行长距离海洋洄游的选择压力正在发生变化。与许多其他行为特征不同，洄游的成本是在迁徙者明显获得任何适应度收益之前产生的。因此，这种行为是经过多代选择压力塑造的，不能像许多其他行为特征那样对短时间间隔（在单个世代内）的环境变化做出反应。在这里，我们提供了一个框架来检验迁移成本持续增加的进化和生态后果。我们认为，大西洋鲑可能已经陷入了一个进化陷阱，由于环境条件的变化，长距离海洋洄游已经变得不适应。我们预测，如果迁移成本（影响存活率，最终影响适应度）持续增加，那么选择压力的转变将导致种群规模继续下降。然而，我们认为，在某些种群中，在物种内存在着明显的进化拯救反应能力，这可以从迁移表达的变化中体现出来。在以前促进迁移的选择力发生低到中度变化的情况下，我们认为，破坏性的、基于性别的选择将导致部分迁移，即雌性保留海洋洄游，但雄性的溯河产卵功能丧失。在选择力更为强烈的情况下，溯河产卵可能会受到强烈的选择压力，在这种情况下，雌雄两性都可能变成淡水居留。我们认为，由于洄游成本在有静水的流域似乎更高，因此这种情况在这些系统中更有可能发生。我们还推测，由于该物种的遗传结构，并非所有种群都有足够的能力对变化做出反应。我们讨论了这对该物种及其管理的影响。
