Hypothesis 2- The deer of St. John may have high levels of genetic diversity due to an infusion of heterogeneous loci in the recent past.
White-tailed deer are one of the most abundant of all New World deer species, and one that enjoys a pandemic distribution (Heffelfinger 2011). Due to this vast geographic distribution, phenotypic and genotypic variations exist throughout their range due to either isolation, phenotypic plasticity, and/or adaptations to local habitat, forage, and climactic conditions, resulting in 38 recognized subspecies (Strickland and Demarais 2008; Heffelfinger 2011). In addition, white-tailed deer have been the been part of domestic and international restoration and translocation programs that have further increased their allelic diversity globally. For example, the deer in the state of Virginia were restocked from deer in eleven separate states, and each state received hundreds of deer from Wisconsin as part of restocking programs (Marchinton et al. 1995). Furthermore, the number of alleles per locus for white-tailed deer were found to be significantly different from those of mammals in general (Breshears et al. 1998), further influencing the genetic architecture of deer populations.
The history of the deer on St. John states that additional deer were brought to St. Thomas and St. John from Texas and the Carolinas in the 1950s as part of a USDA translocation program (Baker 1984; Heffelfinger 2011). Both the Texas and Carolina deer populations are noteworthy in their levels of genetic heterogeneity either due to geography or isolation (Erickson 1979; Hillestad 1984). In addition to the Carolina and Texas deer populations being restocked, the Texas population has not experienced any kind of a population bottleneck that reduced its allelic diversity (Erickson 1979; Rhodes and Smith 1992) resulting in a highly genetically diverse source population. Genetic heterogeneity among deer populations is generated over short geographical distances, sometimes as little as 5 km (Sheffield et al. 1985), which is unexpected for this large and highly mobile species (Smith et al. 2001). As a result, a high degree of genetic heterozygosity found within deer populations translates into differences in disease resistance and immune response among deer subspecies (Gaydos et al. 2002; Johnson et al. 2006).
Therefore, perhaps the genetic diversity of the St. John deer after approximately 200 years is not as low as expected due to the influx of highly heterogeneous alleles that came from the infusion of deer from source populations in Texas and the Carolinas in the 1950s. This diversity, coupled with the short duration of time since their infusion into the current population, (approximately 70 years), may have added a significant amount of genetic diversity of deer currently living on St. John.