Landscape‐Genetic Analysis of Population Structure in the Texas Gray Fox Oral Rabies Vaccination Zone

Abstract

In west‐central Texas, USA, abatement efforts for the gray fox (Urocyon cinereoargenteus) rabies epizootic illustrate the difficulties inherent in large‐scale management of wildlife disease. The rabies epizootic has been managed through a cooperative oral rabies vaccination program (ORV) since 1996. Millions of edible baits containing a rabies vaccine have been distributed annually in a 16‐km to 24‐km zone around the perimeter of the epizootic, which encompasses a geographic area >4 × 105 km2. The ORV program successfully halted expansion of the epizootic into metropolitan areas but has not achieved the ultimate goal of eradication. Rabies activity in gray fox continues to occur periodically outside the ORV zone, preventing ORV zone contraction and dissipation of the epizootic. We employed a landscape‐genetic approach to assess gray fox population structure and dispersal in the affected area, with the aim of assisting rabies management efforts. No unique genetic clusters or population boundaries were detected. Instead, foxes were weakly structured over the entire region in an isolation by distance pattern. Local subpopulations appeared to be genetically non‐independent over distances >30 km, implying that long‐distance movements or dispersal may have been common in the region. We concluded that gray foxes in west‐central Texas have a high potential for long‐distance rabies virus trafficking. Thus, a 16‐km to 24‐km ORV zone may be too narrow to contain the fox rabies epizootic. Continued expansion of the ORV zone, although costly, may be critical to the long‐term goal of eliminating the Texas fox rabies virus variant from the United States.

Temporal Analysis of Genetic Structure to Assess Population Dynamics of Reintroduced Swift Foxes

“…The degree of risk of extirpation depends on N e and on the population growth rate following reintroduction (Keller et al ). Our measures of swift fox diversity showed heterozygosity is high relative to many reintroduced species ( H o = 0.504, Lance et al ; H o = 0.50, Tokarska et al ) and is comparable to other extant fox species (Schwartz et al ; DeYoung et al ), including swift foxes in Colorado ( H o = 0.542, Kitchen et al ). However, these comparisons are relative because the estimate of heterozygosity depends on many factors that include marker choice, sample size, and analytical method (Hedrick ).…”

Oral Rabies Vaccination in North America: Opportunities, Complexities, and Challenges

“…Subsequent intervention with TVR has resulted in periods of quiescence followed by reemergence in 2004 and 2005 [21], and again in 2008 [59]. From 31 October 2008 – 1 May 2009, 17 cases of the same big brown bat variant were confirmed in gray fox, a species capable of longer range movement that could facilitate establishment of this variant in foxes and skunks over a broader geographic area [60],[61]. While these events support the hypothesis of a viral host shift from bats to carnivores, they also raise questions about the potential relationship between human perturbations that contributed to a locally abundant skunk population near Flagstaff and the development of this situation.…”

Effect of compensatory immigration on the genetic structure of coyotes

“…In addition to disruption of genetic structure, trapping may also alter the distribution of related individuals. Prior to trapping, we expected related coyotes to exhibit genetic signatures of philopatry (i.e., related individuals are found close together) as observed in other canids (Kitchen et al 2005, DeYoung et al 2009, Stronen et al 2012). Thus, we expected trapping of resident animals to alter the genetic signature of philopatry between pre-and post-trapping years, especially if the recolonizing coyotes were unrelated transients.…”