Climate change can drive rapid evolution in species by drastically transforming their habitats. In recent decades, California has experienced severe drought punctuated by heavy rainfall, causing extreme variation in coastal river and estuary ecosystems. Typically, rivers flow into bar-built estuaries, which seasonally breach to the ocean when winter and spring rainfall cause an influx of water. As drought becomes common, especially in southern California, rivers meet the ocean less frequently and remain isolated for longer. Thus, drought is likely altering estuary ecosystems, which changes not only biological communities, but also the evolution of species. Threespine Stickleback (Gasterosteus aculeatus) are small fish that inhabit these coastal rivers and estuaries across California and can adapt rapidly to different water conditions, such as temperature and salinity. Most research on stickleback contemporary evolution focuses on Northern populations where rivers meet the ocean year-round. In California, however, traits such as anti-predator armor and specialized feeding morphology may correlate with estuary breaching. Thus, genotypic and phenotypic variation may be affected by alternating selection pressures in closed-freshwater versus open-brackish water estuaries, a pattern that likely manifests both temporally (across seasons) and spatially (across latitudes).My project examines the evolutionary and ecological impacts of climate change on rapid adaptation of estuarine threespine stickleback by first, documenting changes in gene frequencies and associated phenotypes in six local estuarine stickleback populations over spring and fall of two years, and second, comparing my own contemporary samples to historical data and samples collected 40 years ago from estuaries and rivers state-wide
Results/Conclusions
My initial results illustrate correlative links among rainfall, estuary breaching, and stickleback phenotype and genotype. Low-plated fish tend to dominate estuaries in dry conditions when estuaries are closed, whereas high-plated fish dominate in wetter conditions when estuaries are open to the ocean. As a result, northern Californian estuaries experiencing higher precipitation have stickleback with more lateral plates than southern, drier estuaries that primarily contain low plated fish. Both fish collected in the 1970s and my current samples follow this pattern, with average plate number declining sharply from north to south along the California coast. Yet, average plate number has decreased in all populations surveyed, and the southern extent of high-plated fish has retracted northward, potentially reflecting recent climate change in the form of increased drought. Our results provide evidence that climate change has contributed to evolution in natural populations over just a few decades.