Eco-evolutionary dynamics may show an irreversible regime shift, illustrated by salmonids facing climate change

Abstract

The enhanced or reduced growth of juvenile masu salmon (Oncorhynchus masou masou) may result from climate changes to their environment and thus impact on the eco-evolutionary dynamics of their life-history choices. Male juveniles with status, i.e., if their body size is larger than a threshold, stay in the stream and become resident males reproducing for multiple years, while those with smaller status, i.e., their body size is below the threshold, migrate to the ocean and return to the stream one year later to reproduce only once. Since juvenile growth is suppressed by the density of resident males, the fraction of resident males may stay in equilibrium or fluctuate wildly over a 2-year period. When the threshold value evolves, the convergence stable strategy may generate either an equilibrium or large fluctuations of male residents. If environmental changes occur faster than the rate of evolutionary adaptation, the eco-evolutionary dynamics exhibit a qualitative shift in the population dynamics. We also investigated the relative assessment models, in which individual life-history choices are made based on the individual’s relative status within the juvenile population. The eco-evolutionary dynamics are very different from the absolute assessment model, demonstrating the importance of understanding the mechanisms of life history choices when predicting the impacts of climate change.

Individual-based eco-evolutionary models for understanding adaptation in changing seas

“…Studies highlighted critical issues that need to be addressed, particularly if results would be used to inform management and conservation. Three themes emerged across studies, which we discuss further: (i) the need to better understand effects of genetic architecture and non-genetic responses on adaptation [32][33][34][35]; (ii) the need for better integration of dispersal and connectivity [32,34,36]; and (iii) the need to consider multiple stressors given that climate change will likely be accompanied by other challenges [34] and impacts on multiple traits [37] (table 2).…”

“…fish)not explicit, (genetic variance)closed population of philopatric adults, focuses on migration timingNArates of change and variability in optimal migration timing, genetic inheritance, plasticity, bioclimate envelope sizeR: code in electronic supplementary material[36]predict impact of network structure on adaptive potentialgeneric, application to sedentary taxa (e.g. coral)not explicit; (genetic variance)discrete patches, variable network opennessconstantlevels of openness, temperature regime, growth modelNumpy: Zenodo [37]predict impact of climate change on life-history strategy and population dynamicsmasu salmon: Oncorhynchus masou masou not explicit; (genetic variance)closed system, focuses on migratory dynamicsNArate of climate change, the rate of evolution in the key trait, body sizeC: Github …”

“…Although this study focused on a closed population, their model showed that plastic responses reduced the probability of adaptation when genetic variability was low [35]. IBMs of masu salmon ( Oncorhynchus masou masou ), in which life-history strategies (resident versus migrator) are determined by juvenile body size, showed that as climate change impacts growth, adjusting migratory behaviour based on learned relative status could alleviate effects on population dynamics when adaptation to a new size threshold is slow [37]. Matz et al .…”