Population genetics of an invasive species, Sus scrofa: Implications for their behavior and management

The management of the invasive feral pig (Sus scrofa) has been the subject of intense study in recent years.  Feral pigs are considered an exotic invasive in the U.S., where conservative estimates indicate an annual loss of $200/pig due to agricultural damage. Feral pigs are also susceptible to diseases that affect livestock, humans, and wildlife (e.g., brucellosis, pseudorabies). Feral pigs clearly represent a threat to the sustainability of multiple agriculture products. Population reduction (trapping or shooting) is the best current alternative for controlling pig damage. However, reduction is crude and inefficient in terms of manpower and resources because pigs from neighboring areas quickly recolonize managed areas. We used a panel of 9 microsatellite loci to study broad-scale population structure in feral pigs from south Texas and to evaluate recolonization after a local removal. At a broad scale (>200 km), pig populations displayed a moderate degree of genetic structure (Fst = 0.16), suggesting that at broad geographic scales, populations are differentiated enough to be functionally independent. However, genetic similarity was not a simple function of geographic distance, implying that movement and dispersal are not equal among populations.  This may be due to the presence of terrain features that promote (e.g., river systems) or inhibit (e.g., urban areas, farmland areas) dispersal.  At a local scale, animal samples taken before and after a removal event were genetically different (Fst = 0.08), indicating rapid recolonization occurred into the controlled area. Overall, our results indicate that knowledge of population structure in south Texas could be used to improve pig control efforts, but high rates of movement and dispersal in other areas would likely require control efforts over a very broad region, possibly an entire watershed.  Ongoing efforts will attempt to identify fine-scale genetic structure and landscape features that could be used to focus management efforts.