Adaptive divergence despite strong genetic drift: genomic analysis of the evolutionary mechanisms causing genetic differentiation in the island fox (Urocyon littoralis).

The evolutionary mechanisms generating the tremendous biodiversity of islands have long fascinated evolutionary biologists. Genetic drift and divergent selection are predicted to be strong on islands and both could drive population divergence and speciation. Alternatively, strong genetic drift may preclude adaptation. We conducted a genomic analysis to test the roles of genetic drift and divergent selection in causing genetic differentiation among populations of the island fox (Urocyon littoralis). This species consists of six subspecies, each of which occupies a different California Channel Island. Analysis of 5293 SNP loci generated using Restriction-site Associated DNA (RAD) sequencing found support for genetic drift as the dominant evolutionary mechanism driving population divergence among island fox populations. In particular, populations had exceptionally low genetic variation, small Ne (range = 2.1-89.7; median = 19.4), and significant genetic signatures of bottlenecks. Moreover, islands with the lowest genetic variation (and, by inference, the strongest historical genetic drift) were most genetically differentiated from mainland grey foxes, and vice versa, indicating genetic drift drives genome-wide divergence. Nonetheless, outlier tests identified 3.6-6.6% of loci as high FST outliers, suggesting that despite strong genetic drift, divergent selection contributes to population divergence. Patterns of similarity among populations based on high FST outliers mirrored patterns based on morphology, providing additional evidence that outliers reflect adaptive divergence. Extremely low genetic variation and small Ne in some island fox populations, particularly on San Nicolas Island, suggest that they may be vulnerable to fixation of deleterious alleles, decreased fitness and reduced adaptive potential.

Seroprevalence of Bartonella spp. in the endangered island fox (Urocyon littoralis).

Bartonella clarridgeiae-like strains, presently B. rochalimae, were isolated in gray foxes (Urocyon cinereoargenteus) in mainland California. The objective of this study was to investigate the presence of Bartonella infection in the endangered island fox (Urocyon littoralis) found only on the Channel Islands off the Californian coast. Between 2001 and 2004, 263 serum samples were collected. Antibodies against Bartonella vinsonii subsp. berkhoffii (Bvb) and B. clarridgeiae (Bc) were detected using an immuno-fluorescence antibody test. Sixty-eight (25.8%) and 73 (27.7%) foxes were positive for Bvb and Bc, respectively. Seroprevalence was the highest on Santa Cruz Island (n=36, Bvb=80.5%; Bc=86.1%) and Santa Rosa Island (n=38, Bvb=52.6%; Bc=65.8%). On San Miguel and San Clemente Islands, seroprevalence for Bvb was 20% and 17.3% respectively, and 0% and 21.3% for Bc. Prevalence ranged between 0% and 5.1% on San Nicolas and Santa Catalina Islands. Foxes from Santa Rosa and Santa Cruz Islands were 17.5 times and 31.5 times as likely to be seropositive for Bvb and Bc than foxes from the other islands (95% confidence interval [95% CI]=8.5, 36.7; 14.4, 70.2). There were no statistically significant differences for presence of Bartonella antibodies by sex, age, origin (captive vs. wild) or year of blood collection. This is the first report of exposure to Bartonella in the island fox population. Further studies are necessary to isolate these bacteria from foxes and determine factors associated with presence or absence of Bartonella species on specific islands.

Pathogen exposure in endangered island fox (Urocyon littoralis) populations: Implications for conservation management.

Island fox (Urocyon littoralis) populations on four California Channel Islands have declined severely since 1994. Canine distemper (CDV) was suspected to be responsible for the decline of the Santa Catalina Island fox, so knowledge of infectious disease exposure in the remaining island fox populations was urgently needed. This study reviewed previous pathogen exposure in island foxes and investigated the current threat by conducting a serologic survey of foxes on all islands and sympatric feral cats on three islands from 2001 to 2003 for antibodies against canid pathogens. Before the decline, foxes had evidence of exposure to CDV, canine adenovirus (CAV), canine parvovirus (CPV), and Toxoplasma, with exposure to these five pathogens differing greatly by island. Exposure to canine coronavirus (CCV), canine herpesvirus (CHV), and Leptospira was rare. In 2001-2003, wild-born foxes had evidence of exposure to CDV (5.2-32.8%) on 5 of 6 islands, CPV (28-100%) and CAV (4.7-100%) on five islands, and Toxoplasma gondii (2.3-15.4%) on four islands. Exposure to CCV, CHV and Leptospira was less common. Sharing of infectious agents between sympatric foxes and feral cats appeared minimal, but CDV exposure was detected in two cats on Santa Catalina Island. Domestic dogs have historically been present on the islands, but it is not known if canine diseases can be maintained in fox populations without the continual presence of dogs. Targeted vaccination programs against the most virulent pathogens and continued intensive disease surveillance may help protect the critically small remaining fox populations from disease outbreaks that could threaten the success of ongoing conservation efforts.

Biochemical and hematologic reference intervals for the endangered island fox (Urocyon littoralis).

Hematologic and serum biochemical data collected must be interpreted by comparison with normal reference intervals generated from healthy animals, within a similar population, because many blood parameters are influenced by diet, environment, and stress. Species-specific reference intervals for the endangered island fox (Urocyon littoralis) are not available. We reviewed hematology and serum biochemistry panels from 280 island foxes sampled from 1999-2008 and established normal reference intervals from clinically healthy foxes using a nonparametric approach. Blood parameters were analyzed for differences in age, sex, island of origin, and captivity status. Alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, and creatine kinase activities, as well as calcium and phosphorus concentrations, were significantly higher in juveniles than in adults, but total protein and globulin concentration was lower for juveniles than for adults. Lymphocyte and eosinophil counts, and blood urea nitrogen (BUN) concentration, in foxes from the northern Channel islands of California, USA (Santa Cruz, Santa Rosa, and San Miguel) were higher when compared with foxes from Santa Catalina Island to the south. Higher lymphocyte and eosinophil numbers in the northern island foxes may be associated with increased levels of parasitism on the northern islands. Differences in BUN concentration in both free-ranging and captive foxes may reflect dietary differences among islands. Although aggressive conservation programs have been enacted, island foxes are still susceptible to infectious and neoplastic diseases and, potentially, to toxins. Island fox species-specific reference intervals will enable managers and veterinarians to better care for sick and injured foxes and will contribute to future population health monitoring.

Isolation or detection of Bartonella vinsonii subspecies berkhoffii and Bartonella rochalimae in the endangered island foxes (Urocyon littoralis).

Bartonella rochalimae (B.r.) and Bartonella vinsonii subsp. berkhoffii (B.v.b.) have been isolated from gray foxes (Urocyon cinereoargenteus) in mainland California and high Bartonella seroprevalence was reported in island foxes (U. litorralis), especially from Santa Cruz and Santa Rosa Islands. As a follow-up study, the objectives were to determine the prevalence of Bartonella bacteremia and seropositivity and to identify the Bartonella species infecting a convenience sample of 51 island foxes living on Santa Rosa Island. Using an immuno-fluorescence antibody test directed against B.v.b and Bartonella clarridgeiae (B.c.), used as a substitute for B.r., the overall antibody prevalence was 62.7% with 16 (31.4%) foxes seropositive for B.c. only, 5 (9.8%) for B.v.b. only, and 11 (21.6%) for both antigens. B.v.b. was isolated from 6 (11.8%) foxes using blood culture medium. An additional seropositive fox tested PCR positive for B.v.b. and 3 other seropositive foxes tested PCR positive for B. rochalimae. All of the isolated B.v.b. colonies and the B.v.b. PCR positive sample belonged to type III, the same type found to infect mainland gray foxes. Therefore, Bartonella infection is widespread within this island fox population with evidence for B.v.b. type III reservoir host-specificity. Presence of B. rochalimae in the Channel Islands has been detected for the first time using PCR.