Genetic population structure of invasive nutria (Myocastor coypus) in Louisiana, USA: is it sufficient for the development of eradication units?

The effective control of invasive mammals, because of their potentially high dispersive capacity, demands an understanding of spatial patterns of gene flow leading to the designation of population units for systematic eradication. Nutria, or coypu (Myocastor coypus), are large, semi-aquatic rodents, originally exported from their native South America for the value of their fur, and are now considered pests on many continents due to overgrazing of wetlands. This study was aimed at assessing the potential for establishing eradication units for the control of nutria in a severely impacted region of the US, southern Louisiana, using nine microsatellite loci, and systematic sampling from each of eight major watershed basins. Unexpectedly high levels of genetic diversity were revealed in comparison to native populations both in terms of numbers of alleles and observed heterozygosities, suggesting that multiple source populations may have originally contributed to the establishment of the Louisiana fur trade, which have subsequently become intermingled. Genetic differentiation among watersheds was nearly undetectable, as evidenced by a very small, albeit significant overall FST value of 0.0059. Interestingly, one of the Bayesian clustering algorithms used in this study identified 11 populations that may represent a fading remnant of the original source populations, although these clusters were not supported by a coherent pattern of geography. Unfortunately, these findings suggest that neither the establishment of locally manageable eradication units, nor the development of biological control agents known for their close association with a single source population will be effective in the control of Louisiana nutria.