Factors Influencing Raccoon Rabies Spread During the 1950s-1970s Raccoons are clearly heterogeneous throughout the RRV endemic area. Since the limitation to raccoon dispersal appears to have occurred much earlier than the period of time when RRV spread across the southeastern US, other ecological factors such as population density or resource distribution may have contributed to its relatively slow progression during the 1950s–1970s. Cullingham et al. (2008) claimed that there is little contemporary gene flow into Florida despite the absence of an obvious barrier and suggested that landscape shape is responsible for raccoon dispersal and the slow spread of the RRV in the southeast. Cullingham’s study (2008) was based solely on mitochondrial DNA, however, and highlights the importance of examining both mitochondrial and nuclear markers to gain a complete understanding of a population’s evolutionary history. In the current study, we found evidence of historical isolation of Florida raccoons but recent gene flow among raccoons in the southeastern US. This would argue against limited gene flow in this region and would not fully explain landscape shape as a factor in the 20+ years it took for RRV to spread from Florida into Alabama, Georgia, and South Carolina. Raccoon density is another possibility for the slow progression of the virus during the 1950s-1970s; however, raccoon densities vary considerably and are often due to differences in habitat quality or resource distribution. While a lower raccoon population density in the southern US has been hypothesized to explain the variation in RRV spread, exceptions to this generality are easy to find. For example, raccoon density at an urban park in Florida (Xxxxx and Xxxxxxx 2002) is 2.5 times higher than the raccoon density in northern Ohio (Xxxxx et al. 2008). Although raccoons are generalists and are capable of exploiting a variety of habitats (Zeveloff 2002), differences in resource distribution and/or habitat quality may cause spatial aggregation and could affect population density estimates, contact rates, and the potential for RRV transmission. Interestingly, raccoons in northern Florida share haplotypes with individuals in Georgia and Tennessee but fail to share any mitochondrial haplotypes with raccoons in Alabama, the southwestern edge of RRV’s current range. Future studies should examine additional raccoons in Alabama, Mississippi, and in other western localities to determine the significance of this trend. Given the range of raccoons in population 2,...
