1024 Conservation Biology, Pages 1024–1035 Volume 16, No. 4, August 2002 Genetic Diversity in a Morphologically Conservative Invasive Taxon: Multiple Introductions of Swamp Eels to the Southeastern United States TIMOTHY M. COLLINS,*‡ JOEL C. TREXLER,* LEO G. NICO,† AND TIMOTHY A. RAWLINGS* *Department of Biological Sciences, Florida International University, University Park, Miami, FL 33199, U.S.A., †United States Geological Survey, Florida Caribbean Science Center, 7920 NW 71st Street, Gainesville, FL 32653, U.S.A. Abstract: Genetic analysis of introduced populations, especially in morphologically conservative taxa, can clarify introduction histories, identify management units and source populations, provide a more realistic es- timate of the frequency of successful invasion, and suggest strategies for preventing further introductions. In the last 7 years, populations of swamp eels, referred to the Asian genus Monopterus (Family Synbranchidae) on the basis of external morphology, have been discovered in aquatic habitats near Atlanta, Georgia; Tampa, Florida; North Miami, Florida; and most recently in close proximity to Everglades National Park in Home- stead, Florida. Swamp eels are large predators capable of dispersal over land and have the potential to dis- rupt already threatened ecosystems. We analyzed mitochondrial DNA sequences from four known popula- tions in the continental United States and samples from Malaysia, Indonesia, Vietnam, and two locations in China to determine introduction histories, source populations, genetic diversity, and relationships among populations. Our results indicate that there have been at least three independent introductions of genetically distinct forms. Introduced populations in close proximity (separated by 40 km) are genetically distinct. The level of sequence difference among introduced populations reaches levels seen among sister families of teleost fishes for the same region of the mitochondrial genome. These genetically distinct introduced populations in all likelihood represent at least two and possibly three species. Regardless of species status, these genetically distinct lineages may be expected to vary in ecological or life-history traits, representing different potential threats to the ecosystems where they have been introduced. Given the success of swamp eels in invading many habitats around the world, further study of these eels is warranted to elucidate the characteristics of successful invaders and invasions. Diversidad Genética en un Taxón Invasivo Morfológicamente Conservativo: Introducciones Múltiples de Anguila de Pantano en el Sureste de Estados Unidos Resumen: El análisis genético de poblaciones introducidas, especialmente en taxones morfológicamente conservativas, puede clarificar la historia de las introducciones, identificar unidades de manejo y pobla- ciones fuente, proporcionar una estimación más realista de la frecuencia de invasiones exitosas y sugerir es- trategias para prevenir introducciones futuras. En los últimos 7 años, se han descubierto poblaciones de an- guilas de pantano, referidas al género Asiático Monopterus (Familia Synbranchidae) con base en su morfología externa, en los hábitats acuáticos cerca de Atlanta, Georgia; Tampa, Florida; Miami Norte, Florida y más re- cientemente muy cerca del Parque Nacional Everglades en Homestead, Florida. Las anguilas de pantano son grandes depredadores capaces de dispersarse por tierra y tienen un potencial para alterar ecosistemas de por si amenazados. Analizamos secuencias de ADN mitocondrial de cuatro poblaciones conocidas en Estados Un- idos y muestras de Malasia, Indonesia, Vietnam y dos localidades en China para determinar la historia de las introducciones, poblaciones fuente, diversidad genética y relaciones entre las poblaciones. Nuestros resultados ‡email collinst@fiu.edu Paper submitted April 17, 2001; revised manuscript accepted September 19, 2001.