The case for conserving threespine stickleback populations: Protecting an adaptive radiation

The threespine stickleback (Gasterosteus aculeatus) comprises a complex of geographically differentiated populations, including some that are clearly separate biological species. The CC complex includes marine and anadromous forms thought to represent the phenotypes that have given rise post-glacially to widely distributed, differentiated, freshwater isolates. The relative uniformity of the marine and anadromous forms permits determination of the direction of evolutionary change in the freshwater radiation. A second feature that is exceptionally valuable for evolutionary inference is the repeated, independent evolution of similar phenotypes under similar ecological conditions. This property of the radiation facilitates evaluation of the causes of evolutionary diversification and speciation. We argue that the value of individual populations of this fish is elevated by their membership in the adaptive radiation, and that each population must be viewed as an integral part of this system, rather than just as a population whose properties are replicated in other lakes. This view requires special conservation status for the stickleback radiation as a whole, and we suggest procedures for protecting this adaptive radiation that we view as reasonable, given that we cannot hope to preserve every population in its pristine state.