Meeting Abstract
Populations inhabiting different environments often display phenotypic and genetic differentiation associated with local conditions. Many well-known examples of local adaptation exist from freshwater fish populations occupying varying environments, such as lake versus stream ecotypes. Identifying the adaptive potential of freshwater fish populations is critical, given anthropogenic habitat modification and climate change. However, population-level differentiation has rarely been documented in darters, one of the most species-rich clades of fish in North America. This study assessed fine-scale phenotypic and genetic variation in Etheostoma caeruleum (rainbow darters), including a unique lake population. We collected individual data for several phenotypes, including thermal tolerance, morphology, boldness, and locomotion. We characterized neutral and potentially adaptive variation using a modified RADseq protocol. Initial analyses indicate population differentiation for thermal tolerance matching habitat temperature, suggesting local adaptation. We also found a significant pattern wherein populations harbouring more genetic variation have higher thermal tolerance. Furthermore, we found significant lake-stream morphological divergence associated with mouth position, supporting ecotypic differentiation. Despite the small geographic scale, we find evidence of fine-scale genetic structure and recent admixture not owing to stream connectivity. We are currently exploring further ecotype divergent phenotypes and putatively adaptive outlier loci associated with the lake population of rainbow darters.
