The Threespine stickleback a diverse key species for the Lake Mývatn ecosystem

Abstract Biological diversity across hierarchical levels (e.g. genes and populations to communities and ecosystems) is the result of dynamic interactions between ecological, developmental and evolutionary processes. Detailed long-term studies of ecosystems in the wild are important for a holistic understanding of how biological diversity and ecosystem function are affected by natural and anthropogenic changes, Lake Mývatn, Northeast Iceland, is an exceptionally well-studied ecosystem with decades long time series data across multiple trophic levels, including threespine stickleback ( Gasterosteus aculeatus ), a keystone fish species in this ecosystem. Here we synthesise knowledge of ecological importance and evidence for intraspecific diversity of stickleback in Mývatn, and discuss its role as a potential mediator of eco-evolutionary feedbacks. In terms of ecology, the population density of stickleback fluctuates strongly over time and varies across different habitats in the lake. Stickleback have a key role across different trophic levels: they are important prey for birds and fish, hosts for various parasite, as well as effective predators on invertebrates and likely have considerable impact on invertebrate and vertebrate populations of Mývatn. The stickleback of Mývatn is a generalist species, which shows evidence of subtle phenotypic and genetic divergence across habitats (likely due to periodically strong dispersal and subsequent gene flow), but substantial phenotypic and genetic change across years (indicating potential for microevolution in response to strong temporal environmental changes). We discuss different sources of variation in stickleback ecology, as well as the potential for stickleback to mediate feedbacks between ecological and evolutionary processes in this spatio-temporally dynamic lake ecosystem.