Meeting Abstract
The interaction of larval transport and post-settlement selection on marine population connectivity influences how local adaptations arise in the face of gene flow. In the waterfall-climbing Hawaiian fish, Sicyopterus stimpsoni, larvae hatch upstream, are swept to the ocean and develop for months before returning to streams. Migration upstream requires climbing of waterfalls before reaching predator-free habitats. The environments to which juveniles return differ between the youngest (waterfalls close to shore, placing a premium on climbing ability) and the oldest (waterfalls far inland, placing a premium on predator evasion) islands. However, larvae from different islands may mix in the ocean, resulting in high gene flow and little differentiation between subpopulations. We developed spatially-explicit individual-based models for the islands of Hawai’i, O’ahu and Kaua’i coupled with a Lagrangian transport model for the Hawaiian Islands. We examined how topography, stream flow, predation, and immigration influenced optimal phenotype evolution and the rate of evolution. Immigration and emigration is largely unidirectional from Hawai’i to Kaua’i. All levels of immigration resulted in diminished rates of evolution of optimal phenotypes across all streams and islands. However, phenotypes conferring improved climbing performance on Hawai’i and O’ahu evolved even with high immigration rates. However, phenotypes conferring improved predator evasion on Kaua’i did not evolve. Our results suggest that a combination of local retention and environmental selection contribute to the potential for locally adapted phenotypes to evolve despite the high degree of gene flow between islands.
