Trophic niche differentiation and phenotypic divergence among cryptic species of Japanese ninespine sticklebacks

摘要

Background: Morphologically similar cryptic species often differ in ecological niches. Three cryptic species of ninespine stickleback (genus Pungitius), P. tymensis and the freshwater and brackish types of the P. pungitius-P. sinensis species complex are found in eastern Hokkaido, Japan. All three co-occur in river catchments, inhabiting the upstream (P. tymensis), midstream (freshwater P. pungitius-P. sinensis type), and downstream (brackish P. pungitius-P. sinensis type).