Expanding the silverside system to quantify how climate gradients determine co- and countergradient adaptation strength in the ocean

Many species have evolved adaptations to latitudinal climate gradients and studying these sheds light on how species will evolve in response to global climate change. To investigate adaptation in Chilean silversides, offspring of wild fish from four locations along the Chilean coast are being reared at four common temperatures. Differences in growth rates, vertebral number, and mercury uptake among populations from different latitudes indicate genetic differences due to local adaptation. The research team is integrating these Chilean silverside data with prior data from northern hemisphere silverside species to better understand the relationship between climate gradient strength and adaptation strength. This project provides training for two graduate students through a US-Chile graduate cross-cultural exchange. The research is being integrated into graduate and undergraduate courses taught in Chile and the research team is sharing the results with the public through a website and magazine articles. This project advances understanding of two forms of local adaptation, co-gradient variation (CoGV) and counter-gradient variation (CnGV), which underlie adaptation to large-scale, latitudinal climate gradients. Using a common garden experiment, the team is examining the relationship between temperature and genetic variation in Chilean silversides. Newly-fertilized offspring obtained from wild founders at four locations along the Chilean coast are being reared at four common temperatures to a common juvenile size. Differences among populations in trait measurements (growth capacity, vertebral number, and total mercury concentration) to test the hypotheses that 1) growth capacity increases with temperature and latitude (CnGV) and 2) vertebral number increases with latitude (CoGV). These data are being integrated with existing evidence from northern hemisphere silverside species to determine if there is a relationship between CnGV/CoGV strength and latitudinal gradient strength. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.