Peter A. H. Westley

Evolutionary rescue in a changing world.

Evolutionary rescue occurs when adaptive evolutionary change restores positive growth to declining populations and prevents extinction. Here we outline the diagnostic features of evolutionary rescue and distinguish this phenomenon from demographic and genetic rescue. We then synthesize the rapidly accumulating theoretical and experimental studies of evolutionary rescue, highlighting the demographic, genetic, and extrinsic factors that affect the probability of rescue. By doing so, we clarify the factors to target through management and conservation. Additionally, we identify several putative cases of evolutionary rescue in nature, but conclude that compelling evidence remains elusive. We conclude with a horizon scan of where the field might develop, highlighting areas of potential application, and suggest areas where experimental evaluation will help to evaluate theoretical predictions.

What Invasive Species Reveal about the Rate and Form of Contemporary Phenotypic Change in Nature

Biological invasions are opportunities to gain insight into fundamental evolutionary questions, because reproductive isolation and sudden alterations in selection pressures are likely to lead to rapid evolutionary change. Here I investigate the role played by invasive species in revealing the rate and form of contemporary phenotypic change in wild populations by expanding a database of more than 5,500 rates of phenotypic change from 90 species of plants and animals. Invasive species are frequently used as model organisms and thus contribute disproportionately to available rates of phenotypic change. However, the preponderance of these rates is the consequence of extensive study in a small number of species. I found mixed evidence to support the hypothesis that phenotypic change is associated with time depending on the metric of choice (i.e., darwins or haldanes). Insights from both invasive and native species provide evidence for abrupt phenotypic change and suggest that the environment plays a potentially important role in driving trait change in wild populations, although the environmental influence on the observed trajectories remains unclear. Thus, future work should continue to seek an understanding of the mechanistic underpinnings—both genetic and environmental—of how phenotypic variation allows populations to adapt to rapidly changing global environments.

Fine-scale local adaptation in an invasive freshwater fish has evolved in contemporary time

Adaptive evolutionary change in only a few generations can increase the ability of non-native invasive species to spread, and yet adaptive divergence is rarely assessed in recently established populations. In this study, we experimentally test for evidence of fine-scale local adaptation in juvenile survival and growth among three populations of an invasive freshwater fish with reciprocal transplants and common-garden experiments. Despite intrinsic differences in habitat quality, in two of three populations we detected evidence of increased survival in ‘home’ versus ‘away’ environments with a Bayesian occupancy model fitted to mark–recapture data. We found support for the ‘local’ versus ‘foreign’ criterion of local adaptation as 14 of 15 pairwise comparisons of performance were consistent with local adaptation (p < 0.001). Patterns in growth were less clear, though we detected evidence of location- and population-level effects. Although the agents of divergent ecological selection are not known in this system, our results combine to indicate that adaptive divergence—reflected by higher relative survival of local individuals—can occur in a small number of generations and only a few kilometres apart on the landscape.

Hybridization between genetically modified Atlantic salmon and wild brown trout reveals novel ecological interactions.

Interspecific hybridization is a route for transgenes from genetically modified (GM) animals to invade wild populations, yet the ecological effects and potential risks that may emerge from such hybridization are unknown. Through experimental crosses, we demonstrate transmission of a growth hormone transgene via hybridization between a candidate for commercial aquaculture production, GM Atlantic salmon (Salmo salar) and closely related wild brown trout (Salmo trutta). Transgenic hybrids were viable and grew more rapidly than transgenic salmon and other non-transgenic crosses in hatchery-like conditions. In stream mesocosms designed to more closely emulate natural conditions, transgenic hybrids appeared to express competitive dominance and suppressed the growth of transgenic and non-transgenic (wild-type) salmon by 82 and 54 per cent, respectively. To the best of our knowledge, this is the first demonstration of environmental impacts of hybridization between a GM animal and a closely related species. These results provide empirical evidence of the first steps towards introgression of foreign transgenes into the genomes of new species and contribute to the growing evidence that transgenic animals have complex and context-specific interactions with wild populations. We suggest that interspecific hybridization be explicitly considered when assessing the environmental consequences should transgenic animals escape to nature.

Collective animal navigation and migratory culture : from theoretical models to empirical evidence

Animals often travel in groups, and their navigational decisions can be influenced by social interactions. Both theory and empirical observations suggest that such collective navigation can result in individuals improving their ability to find their way and could be one of the key benefits of sociality for these species. Here, we provide an overview of the potential mechanisms underlying collective navigation, review the known, and supposed, empirical evidence for such behaviour and highlight interesting directions for future research. We further explore how both social and collective learning during group navigation could lead to the accumulation of knowledge at the population level, resulting in the emergence of migratory culture. This article is part of the theme issue ‘Collective movement ecology’.

Among-population variation in adipose fin size parallels the expression of other secondary sexual characteristics in sockeye salmon ( Oncorhynchus nerka )

The small, non-rayed adipose fin is present in eight extant orders of fishes, including the Salmoniformes (salmon and trout) but the functional significance of the trait is unknown. Recent evidence suggests a hydrodynamic function in juvenile salmonids, and observations of sexually dimorphic adipose fin expression and female preference for males with large fins indicate a role in reproduction by mature individuals. To the extent that the adipose fin functions in reproduction, it might be expected to evolve in parallel with other sexually dimorphic traits, such as body depth and jaw length. To test this hypothesis, we quantified adipose fin size of mature male sockeye salmon, Oncorhynchus nerka, among five populations. Populations differed significantly in adipose fin size after correcting for variation in body length and body depth. Adipose fin size tended to parallel the development of other secondary sexual characteristics, but was more closely related to body length and body depth than jaw length. Interestingly, shallow bodied populations from small creeks with high brown bear, Ursus arctos, predation during spawning tended to have smaller size-adjusted adipose fins than populations spawning in deeper water. However, it remains unclear whether adipose fin size is being selected independently of other traits or if it is pleoitropically linked to a trait under selection (e.g., body size or shape).

Collective movement in ecology: from emerging technologies to conservation and management

Recent advances in technology and quantitative methods have led to the emergence of a new field of study that stands to link insights of researchers from two closely related, but often disconnected disciplines: movement ecology and collective animal behaviour. To date, the field of movement ecology has focused on elucidating the internal and external drivers of animal movement and the influence of movement on broader ecological processes. Typically, tracking and/or remote sensing technology is employed to study individual animals in natural conditions. By contrast, the field of collective behaviour has quantified the significant role social interactions play in the decision-making of animals within groups and, to date, has predominantly relied on controlled laboratory-based studies and theoretical models owing to the constraints of studying interacting animals in the field. This themed issue is intended to formalize the burgeoning field of collective movement ecology which integrates research from both movement ecology and collective behaviour. In this introductory paper, we set the stage for the issue by briefly examining the approaches and current status of research in these areas. Next, we outline the structure of the theme issue and describe the obstacles collective movement researchers face, from data acquisition in the field to analysis and problems of scale, and highlight the key contributions of the assembled papers. We finish by presenting research that links individual and broad-scale ecological and evolutionary processes to collective movement, and finally relate these concepts to emerging challenges for the management and conservation of animals on the move in a world that is increasingly impacted by human activity. This article is part of the theme issue ‘Collective movement ecology’.

Combined Effects of Barge Transportation, River Environment, and Rearing Location on Straying and Migration of Adult Snake River Fall-Run Chinook Salmon

AbstractHoming and straying in salmon have been extensively studied, yet it has proven difficult to disentangle the biotic and abiotic factors that influence straying. In the Columbia River basin, some juvenile salmon are collected at dams and transported downstream to increase survival during seaward migration, and as returning adults they experience a range of environmental conditions as they ascend the river. We examined 8 years of PIT tag detection data for hatchery-reared, fall-run Chinook Salmon Oncorhynchus tshawytscha released in the Snake River to evaluate the combined effects of juvenile barging, rearing and release locations, and environmental conditions on adult migration speed and straying below and above the Columbia River–Snake River confluence. Straying to the upper Columbia River was 10–19 times more likely among adults that were barged as juveniles from Snake River dams than among adults that were in-river migrants or that were transported from McNary Dam (below the confluence) as juveni...

Social interactions shape the timing of spawning migrations in an anadromous fish

Mass migrations are found throughout the animal kingdom and are often undertaken by coordinated social groups. However, surprisingly little is known about how social interactions influence migratory timing. Anadromous fishes such as salmon make extensive breeding migrations between marine and freshwater ecosystems. Returning adult salmon tend to move in discrete temporal pulses, which are typically thought to be triggered by abiotic environmental stimuli (e.g. changes in river flow or temperature). However, most studies reveal only weak correlations between abiotic factors and the timing of spawning runs. Here, we demonstrate that social interactions provide a plausible alternative or additional explanation for such patterns. We first provide an example of the phenomenon using 20 years of data on sockeye salmon, Oncorhynchus nerka , ascending a stream in pulses in the absence of any obvious environmental triggers. Next, we present a model that reproduces the pulses observed in the data, simply by including social interactions among individuals. Deviations between the empirical data and the social model results suggest that salmon may alter their individual behaviour in response to annual fluctuations in density. We hope our results, demonstrating the role that social influence can play on migration timing, will motivate further studies exploring how social interactions may shape the movements of other migratory taxa. Understanding how individuals integrate social information with internal and exogenous drivers of migratory behaviour is vital, particularly in the face of a changing climate, which is changing both the cues used for, and the optimal timing of, migrations.

Eco-evolutionary dynamics, density-dependent dispersal and collective behaviour: implications for salmon metapopulation robustness

The spatial dispersal of individuals plays an important role in the dynamics of populations, and is central to metapopulation theory. Dispersal provides connections within metapopulations, promoting demographic and evolutionary rescue, but may also introduce maladapted individuals, potentially lowering the fitness of recipient populations through introgression of heritable traits. To explore this dual nature of dispersal, we modify a well-established eco-evolutionary model of two locally adapted populations and their associated mean trait values, to examine recruiting salmon populations that are connected by density-dependent dispersal, consistent with collective migratory behaviour that promotes navigation. When the strength of collective behaviour is weak such that straying is effectively constant, we show that a low level of straying is associated with the highest gains in metapopulation robustness and that high straying serves to erode robustness. Moreover, we find that as the strength of collective behaviour increases, metapopulation robustness is enhanced, but this relationship depends on the rate at which individuals stray. Specifically, strong collective behaviour increases the presence of hidden low-density basins of attraction, which may serve to trap disturbed populations, and this is exacerbated by increased habitat heterogeneity. Taken as a whole, our findings suggest that density-dependent straying and collective migratory behaviour may help metapopulations, such as in salmon, thrive in dynamic landscapes. Given the pervasive eco-evolutionary impacts of dispersal on metapopulations, these findings have important ramifications for the conservation of salmon metapopulations facing both natural and anthropogenic contemporary disturbances. This article is part of the theme issue ‘Collective movement ecology’.