Nature and nurture: considering the ecological and evolutionary origins of fish migration

Study of migratory fishes reveals the deep history of genetic predispositions in shaping and informing migratory species richness

Data resources used via GBIF : Occurrences of 33,096 species
Oncorhynchus tshawytscha
Oncorhynchus tshawytscha (Walbaum, 1792) observed in Chico, CA, USA, by sujiar (CC BY-NC 4.0)

Why do some fish migrate? This complex adaptive behaviour is uncommon—migratory fishes are unevenly distributed around the world and represent less than seven per cent of all species—and, as for humans, it can come with heavy costs on the individual.

Describing migratory strategies is itself a challenge. Organized with reference to feeding and reproduction and the environments in which they occur, the life histories characterized within the five accepted categories (amphidromy, anadromy, catadromy, oceanodromy and potamodromy) defy clear and precise distinctions. As a result, revealing possible explanations for migration demands a holistic approach—such as the one delivered by the Chilean authors of this study.

To review current understanding of patterns of migratory fish diversity, they developed a set of global species richness matrices relying on all available native-range records from OBIS and GBIF for migratory species in the class Actinopterygii. The decision to limit their analysis to ray-finned fishes equipped them to include evolutionary data, in the form of an extensive phylogeny for Actinopterygii, alongside climate and environmental data.

Testing for direct relationships between migration and productivity (provisioning, scarcity and precipitation), the study found links between dynamic, resource-rich settings and migratory species richness, except for anadromous species that ascend rivers to breed and potamodromous freshwater migrants. Meanwhile, temperature appears less important when considered with other variables. And while no single factor can explain the "migratoriness" of a given species, the authors' inclusion of evolutionary signals from phylogenetic data reveals how critical the deep history of genetic predispositions is in shaping and informing migratory species richness.

Alò D, Lacy SN, Castillo A, Samaniego HA and Marquet PA (2020) The macroecology of fish migration. Global Ecology and Biogeography. Wiley, 99–116. Available at: