Local adaptation in parapatric and sympatric mosaic coastal habitats through trait divergence of Setaria viridis

This study aimed to determine how coastal variants of plants arise from local populations under natural selection by studying variations in phenotypic variations and survival of Setaria viridis populations inhabiting mosaic environments of two seashores in Japan. S.viridis populations comprised five coastal variants showing significantly higher salt spray tolerance than the inland variant: ST, short and tolerant (common variant); TM, tall and mid-tolerant (Inland Sea); TT, tall and tolerant; PT, prostrate and tolerant; L, extremely late flowering; I, inland and susceptible variants. These variations imply that maritime plants first acquired salt spray tolerance for survival, after which compact plants evolved in habitats where strong winds caused damage from salt spray. Results indicate that diverse intensities of salt spray and winds as well as summer drought generated various coastal variations in parapatry and sympatry.

Methods
To identify adaptive traits, common garden experiments were performed to determine the variations in morphology, salt spray tolerance, and flowering time among populations in four adjacent habitats at two localities. To determine selective agents and their adaptation, field transplant experiments were performed for inland and coastal variants. Population dynamics and flowering phenology were monitored to detect damage from seasonal selections. Finally, the inheritance of adaptive traits was tested by examining the variation in adaptive traits of four F2 populations.