Genetic Dissection Of An Invasive Hybrid Swarm
Biological invasions are a global threat to aquatic biodiversity. Of particular concern are invasive freshwater fishes because they have high establishment rates, and introductions can result in the displacement and extirpation of native species through a range of processes including competition and hybridization. Though it is well known that invasive freshwater fishes commonly spread following introduction events, little is known about how fast and far they may move. Additionally, observations of hybridization involving invasive stream fishes have been linked to elevated turbidity; however, the extent to which impaired water clarity influences reproductive isolation among invasive and native species remains poorly understood. To better understand how invasive freshwater fishes disperse, and how turbidity affects reproductive isolation between native and non-native species, I carried out a series of three related studies. First, I evaluated genetic variation across the native and invasive ranges of red shiner (Cyprinella lutrensis), throughout the United States. Second, I characterized genetic variation and clinal stability across a hybrid swarm involving native blacktail shiner (Cyprinella venusta stigmatura) and invasive red shiner in the Upper Coosa River Basin (UCRB), USA. Third, I examined whether turbidity influences pre-mating social interactions between invasive red shiner and native blacktail shiner. MtDNA haplotypes from native range populations of red shiner form four divergent lineages and suggest that introduced populations in the western and eastern US originate from dissimilar genetic lineages. I also recovered a previously undescribed lineage of Cyprinella that has been cryptically introduced into the western US. Examination of the hybrid swarm in the UCRB revealed that the proportion of hybrids increased between 2005 and 2011, and that the hybrid swarm is continuing to expand both upstream and downstream. Under turbid conditions, I found that pre-mating social interactions increased, and that native blacktail shiner females are especially likely to interact with invasive red shiner males. Localized control or removal may be effective in managing non-native red shiner; further monitoring, however, is needed to help identify additional factors contributing to hybrid swarm movement. Furthermore, integrating knowledge of species behavior into management planning could help deter the further establishment and spread of invasive red shiner.