Cause or consequence? Exploring the role of phenotypic plasticity and genetic polymorphism in the emergence of phenotypic spatial patterns of the European eel

Abstract

The European eel (Anguilla anguilla), and generally, temperate eels, are relevant species for studying adaptive mechanisms to environmental variability because of their large distribution areas and their limited capacity of local adaptation. In this context, GenEveel, an individual-based optimization model, was developed to explore the role of adaptive phenotypic plasticity and genetic-dependent habitat selection, in the emergence of observed spatial life-history traits patterns for eels. Results suggest that an interaction of genetically and environmentally controlled growth may be the basis for genotype-dependent habitat selection, whereas plasticity plays a role in changes in life-history traits and demographic attributes. Therefore, this suggests that those mechanisms are responses to address environmental heterogeneity. Moreover, this brings new elements to explain the different life strategies of males and females. A sensitivity analysis showed that the parameters associated with the optimization of fitness and growth genotype were crucial in reproducing the spatial life-history patterns. Finally, it raises the question of the impact of anthropogenic pressures that can cause direct mortalities but also modify demographic traits and act as a selection pressure.

Freshwater eels: A symbol of the effects of global change

“…These glass eels also display a more gregarious and less aggressive behaviour (Geffroy & Bardonnet, ). Habitat selection could be a trade‐off between growth (generally higher in downstream habitats), survival (generally higher in upstream habitats), competition avoidance (higher competition in downstream habitats) and energetic cost of migration (Drouineau et al., ; Edeline, ; Mateo, Lambert, Tétard, Castonguay, et al., ). Habitat selection is also partly related to genetic or epigenetic polymorphism (Côté et al., ; Gagnaire et al., ; Mateo, Lambert, Tétard, Castonguay, et al., ; Pavey et al., ; Podgorniak, Milan, et al., ).…”

“…Habitat selection could be a trade‐off between growth (generally higher in downstream habitats), survival (generally higher in upstream habitats), competition avoidance (higher competition in downstream habitats) and energetic cost of migration (Drouineau et al., ; Edeline, ; Mateo, Lambert, Tétard, Castonguay, et al., ). Habitat selection is also partly related to genetic or epigenetic polymorphism (Côté et al., ; Gagnaire et al., ; Mateo, Lambert, Tétard, Castonguay, et al., ; Pavey et al., ; Podgorniak, Milan, et al., ). In such a scheme, habitat selection would be the result of a fitness optimization process in which fitness in a habitat would depend on habitat characteristics, competition in the habitat, but also individual variability of growth rates due to the existence of genetically distinct clusters of individuals (Côté et al., ; Mateo, Lambert, Tétard, Castonguay, et al., ).…”

“…Habitat selection is also partly related to genetic or epigenetic polymorphism (Côté et al., ; Gagnaire et al., ; Mateo, Lambert, Tétard, Castonguay, et al., ; Pavey et al., ; Podgorniak, Milan, et al., ). In such a scheme, habitat selection would be the result of a fitness optimization process in which fitness in a habitat would depend on habitat characteristics, competition in the habitat, but also individual variability of growth rates due to the existence of genetically distinct clusters of individuals (Côté et al., ; Mateo, Lambert, Tétard, Castonguay, et al., ).…”

“…These correlations are thought to result from spatially variable selection (some individuals are genetically more adapted than others to survive in some habitats) or of genetically based habitat selection (some types of individuals tend to settle preferentially in some habitats to maximize their fitness). The existence of genetically distinct types of individuals which are more or less adapted to the different types of habitats available within their distribution area (northern vs southern habitats, marine vs brackish vs freshwater habitats), that is ecotypes (Pavey et al., ), combined with a large phenotypic plasticity are assumed to play the main role in eel adaptive capacity, enabling the species to address the wide environmental heterogeneity at both the distribution and catchment scale (Drouineau et al., ; Mateo, Lambert, Tétard, Castonguay, et al., ). In such a scheme, individuals are able to grow and survive in a wide range of habitats thanks to phenotypic plasticity but some individuals are more adapted to some habitats than others (ecotypes), and all individuals reproduce together (panmixia) ensuring that ecotypes are reshuffled in each generation.…”

“…On the other hand, all the other anthropogenic pressures tend to affect ecotypes corresponding to more upstream habitats. As such, these anthropogenic pressures reduce the fitness of those individuals and can become an important selective pressure (Mateo, Lambert, Tétard, Castonguay, et al., ; Mateo, Lambert, Tétard, & Drouineau, ). For example, half the American silver eels migrating down the St. Lawrence River, one of the most productive areas for American eel (Casselman, ), have been killed by hydropower dams and fisheries (Verreault & Dumont, ).…”