Methods
St. John is part of the US Virgin Islands which includes St. John, St.
Thomas, St. Croix, and Water Island. St. Thomas is the nearest island
which also contains deer (Figure 1). Virgin Islands National (VINP) park
lies on the island of St. John and comprises 60% of the landmass of the
island. VINP protects one of the largest and most mature tracts of
secondary dry forest in the eastern Caribbean (Ray et al. 1998). The
island vegetation is largely represented by low-to-mid elevation dry
scrub forest on soils with fairly low soil nutrient content (Oswalt et
al. 2006) and is considered marginal habitat for deer. A severe drought
was present on St. John and the surrounding region that lasted for the
duration of 2015 and caused water, food, and environmental stress to the
St. John deer population (Nelson et al. 2017). During the drought, deer
showed signs of stress such as highly elevated tick and mange levels,
muscular atrophy, poor coat quality, weight loss, lethargy, reduced
reproduction, and death (Reuter and Nelson 2018).
DNA samples were collected in two ways, either by collecting hair
samples from deer while they were anesthetized, or by collecting DNA
from fecal samples. To collect hair samples, adult deer were
anesthetized using butorphanol, azaperone, and medetomidine (BAM,
Wildlife Pharmaceuticals, Windsor, Colorado, USA). Only adult does and
bucks were immobilized for this project, no pregnant deer or fawns were
used. Vitals monitored included heart rate, respiratory rate, mucous
membrane color, body temperature, time to recumbency, and recovery.
Following hair collection and after examination, the anesthesia was
reversed with 2–3 mL of atipamezole (25 mg/mL) and 0.5 mL of naltrexone
(50 mg/mL, Wildlife Pharmaceuticals). Deer recovered to standing with
full stability within five minutes (Reuter and Nelson 2018). Hair
samples were individually labelled and placed in coin envelopes in
frozen storage until analysis.
Fecal DNA samples were collected only from freshly deposited fecal
samples with the deer in view. Several toothpicks were rubbed gently
over the surface of the fecal sample for each sample collected. The
samples were allowed to dry and placed in a coin envelopes in frozen
storage until analysis. Research on live animals followed ASM guidelines
(Sikes et al. 2016) and was completed under Scientific Research and
Collection permit VIIS-2016-SCI-0026 for the USVI National Park and the
University of Colorado Boulder and the National Park Service
Institutional Animal Care and Use Committee (1602.01-15Mar2016).
DNA was extracted from both the hair samples using QIAGEN DNeasy Blood
and Tissue kits and following QIAGEN’s tissue protocol. All hair samples
yielded at least 10 guard hair roots (Paetkau 2003). A standard set of
21 microsatellite markers that are used for parentage certification in
game farming applications, and which were found originally in
populations of mainland deer from North Carolina, Wisconsin, and Texas,
were amplified for the 80 adult deer sampled on St. John (Wildlife
Genetics International, Inc.).
Individuals with >10 genotyped microsatellites (N = 42)
were analyzed using GENEPOP (Ver. 4.2) (Raymond and Rousset 1995;
Rousset 2008) to determine number of alleles per locus, observed
heterozygosity, and inbreeding coefficient (FIS) for
comparison to non-island populations of white-tailed deer.