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Red shiner invasion and hybridization with blacktail shiner in the upper Coosa River, USA
WALTERS, DAVID M., M. J. BLUM, B. RASHLEIGH, B. J. Freeman, B. A. Porter, AND N. M. Burkhead. Red shiner invasion and hybridization with blacktail shiner in the upper Coosa River, USA. BIOLOGICAL INVASIONS. Springer Science+Business Media, 10(8):1229-1242, (2008).
Freshwater fish invasions of rivers in the Southeastern U.S. also provide unique opportunities for understanding ecological and genetic consequences of NIAS introductions. EERD has begun a collaborative and interdisciplinary study to evaluate the spread of red shiner (Cyprinella lutrensis) across Southeastern drainages relative to competition and hybridization with endemic blacktail shiners (C. venusta), land use patterns, and stream remediation scenarios. The research is aimed at determining whether spread and introgresive hybridization by C. lutrensisis facilitated by land use impacts on water quality (ie. urbanization and turbidity). Corresponding genetic studies on the longitudinal distribution of C. lutrensis x C. venusta hybridization will further indicate whether land use impacts on water quality correspond to genetic pathways of invasion. Additional laboratory studies on C. lutrensis and C. venusta mate recognition and hybrid fitness are being conducted to experimentally test whether increased turbidity eliminates or weakens interspecific reproductive barriers and increase rates of hybridization. The information gained from these studies will ultimately feed into spatially explicit population models to evaluate how remediation strategies might limit ecological competition and hybridization to maintain drainage specific evolutionary lineages of C. venusta and other native congeners. This research also represents an application of an integrative approach EERD is developing for assessing the condition of aquatic habitats based on landscape, community, and genetic analyses.
Human disturbance increases the invasibility of lotic ecosystems and the likelihood of hybridization between invasive and native species. We investigated whether disturbance has contributed to the invasion of red shiner (Cyprinella lutrensis) and their hybridization with native blacktail shiner (C. venusta stigmatura) in the upper Coosa River System (UCRS). Historical collection records indicated that red shiners and hybrids have rapidly dispersed in the UCRS via large, mainstem rivers since the mid to late 1990s. We measured the occurrence and abundance of parental species and hybrids near tributary-mainstem confluences and characterized populations at these incipient contact zones by examining variation across morphological traits and molecular markers. Red shiners represented only 1.2% of total catch in tributaries yet introgression was widespread with hybrids accounting for 34% of total catch. Occurrence of red shiners and hybrids was highly correlated with occurrence of blacktail shiners, indicating that streams with native populations are preferentially colonized early in the invasion and that hybridization plays a key role in the establishment and expansion of invasive red shiners and their genome into new habitats. Tributary invasion was driven primarily through advanced generation hybrids exhibiting proportionately greater genomic contributions from blacktail shiner. Occurrence of red shiners and hybrids and the relative abundance of hybrids significantly increased with measures of human disturbance including turbidity, catchment agricultural land use, and low dissolved oxygen concentration. Our findings indicate that red shiners pose a serious threat to Southeast Cyprinella species diversity, given that 41% of these species hybridize with red shiner, that five major southeastern drainages have been invaded, and that these drainages are increasingly disturbed by urbanization.