Evolutionary and ecological constraints of fish spawning habitats

For marine fish, the choice of the spawning location may be the only means to fulfil the dual needs of surviving from the egg to juvenile stage and dispersing across different habitats while minimizing predation and maximizing food intake. In this article, we review the factors that affect the choice of fish spawning habitats and propose a framework to distinguish between ecological and evolutionary constraints. We define the former as the boundaries for phenotypically plastic responses to environmental change, in this case the ability of specific genotypes to change their spawning habitat. Processes such as predation, starvation, or aberrant dispersal typically limit the amount of variability in spawning habitat that fish may undergo from 1 year to the next, and thus regulate the intensity of ecological constraints. Evolutionary constraints, on the other hand, refer to aspects of the genetic make-up that limit the rate and direction of adaptive genetic changes in a population across generations; that is, the potential for micro-evolutionary change. Thus, their intensity is inversely related to the level of genetic diversity associated with traits that regulate spawning and developmental phases. We argue that fisheries oceanographers are well aware of, and more deeply focused on, the former set of constraints, while evolutionary biologists are more deeply focused on the latter set of constraints. Our proposed framework merges these two viewpoints and provides new insight to study fish habitat selection and adaptability to environmental changes.