Hybridization and introgression are two important evolutionary mechanisms that can increase genetic diversity. Interesting introgression patterns can form when parental species have genes that confer some adaptive benefit to the organism. The Fundulus notatus species complex contains species with various identifying characterisics. Fundulus notatus, the blackstripe topminnow, and Fundulus olivaceus, the blackspotted topminnow, are closely related and occupy many of the same rivers in their preferred niches. These two species often hybridize and form hybrid zones where their niches overlap. We studied two hybrid zones located in the Tombigbee River and Spring River. Within each hybrid zone, we performed a structure analysis to identify parental species and those of mixed ancestry. We then performed a sliding window analysis to analyze the hybrid genomes present in each hybrid zone. When comparing the two hybrid zones, we identified overlapping regions of low introgression on five chromosomes, whereas we only found one overlapping region of high introgression. We then identified putative functions of genes present within these regions, and most genes in the regions of low introgression had functions in the categories of cell development, intra/intercellular transport, and cell signaling
