Specific alleles at immune genes, rather than genome-wide heterozygosity, are related to immunity and survival in the critically endangered Attwater's prairie-chicken.

The negative effects of inbreeding on fitness are serious concerns for populations of endangered species. Reduced fitness has been associated with lower genome-wide heterozygosity and immune gene diversity in the wild; however, it is rare that both types of genetic measures are included in the same study. Thus, it is often unclear whether the variation in fitness is due to the general effects of inbreeding, immunity-related genes or both. Here, we tested whether genome-wide heterozygosity (20 990 SNPs) and diversity at nine immune genes were better predictors of two measures of fitness (immune response and survival) in the endangered Attwater's prairie-chicken (Tympanuchus cupido attwateri). We found that postrelease survival of captive-bred birds was related to alleles of the innate (Toll-like receptors, TLRs) and adaptive (major histocompatibility complex, MHC) immune systems, but not to genome-wide heterozygosity. Likewise, we found that the immune response at the time of release was related to TLR and MHC alleles, and not to genome-wide heterozygosity. Overall, this study demonstrates that immune genes may serve as important genetic markers when monitoring fitness in inbred populations and that in some populations specific functional genes may be better predictors of fitness than genome-wide heterozygosity.

Decreased small mammal and on-host tick abundance in association with invasive red imported fire ants (Solenopsis invicta).

Invasive species may impact pathogen transmission by altering the distributions and interactions among native vertebrate reservoir hosts and arthropod vectors. Here, we examined the direct and indirect effects of the red imported fire ant (Solenopsis invicta) on the native tick, small mammal and pathogen community in southeast Texas. Using a replicated large-scale field manipulation study, we show that small mammals were more abundant on treatment plots where S. invicta populations were experimentally reduced. Our analysis of ticks on small mammal hosts demonstrated a threefold increase in the ticks caught per unit effort on treatment relative to control plots, and elevated tick loads (a 27-fold increase) on one common rodent species. We detected only one known human pathogen (Rickettsia parkeri), present in 1.4% of larvae and 6.7% of nymph on-host Amblyomma maculatum samples but with no significant difference between treatment and control plots. Given that host and vector population dynamics are key drivers of pathogen transmission, the reduced small mammal and tick abundance associated with S. invicta may alter pathogen transmission dynamics over broader spatial scales.

Indirect effects of red imported fire ants on Attwater's prairie-chicken brood survival.

The invasive red imported fire ant (Solenopsis invicta) has negatively affected a host of taxonomic groups throughout its acquired North American range. Many studies have hypothesized indirect trophic impacts, but few documented those impacts. We evaluated invertebrate abundance as a factor limiting juvenile survival of the endangered Attwater's prairie-chicken (Tympanuchus cupido attwateri), and whether fire ants reduce invertebrate numbers and biomass. From 2009-2013, we monitored survival of Attwater's prairie-chicken broods (n = 63) with radio telemetry during the first 2 weeks post-hatch and collected daily invertebrate samples at brood sites. Broods located in areas with the highest median invertebrate count (338 invertebrates/25 sweeps) had a survival probability of 0.83 at 2 weeks post-hatch compared to 0.07 for broods located in areas with the lowest median invertebrate count (18 invertebrates/25 sweeps). During 2011-2012, we evaluated the reduction of fire ants on invertebrate numbers and biomass by aerially treating areas with Extinguish Plus™ in an impact-reference study design. Treated fields had 27% more individual invertebrates and 26% higher invertebrate biomass than reference fields. Our results clearly document that invertebrate abundance affects Attwater's prairie-chicken brood survival and that fire ants may indirectly contribute to low brood survival by suppressing invertebrate abundance. We posit that within the fire ant's acquired North American range, fire ants are likely contributing to declines of other insectivorous species. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.

A comparison of pedigree- and DNA-based measures for identifying inbreeding depression in the critically endangered Attwater's Prairie-chicken.

The primary goal of captive breeding programmes for endangered species is to prevent extinction, a component of which includes the preservation of genetic diversity and avoidance of inbreeding. This is typically accomplished by minimizing mean kinship in the population, thereby maintaining equal representation of the genetic founders used to initiate the captive population. If errors in the pedigree do exist, such an approach becomes less effective for minimizing inbreeding depression. In this study, both pedigree- and DNA-based methods were used to assess whether inbreeding depression existed in the captive population of the critically endangered Attwater's Prairie-chicken (Tympanuchus cupido attwateri), a subspecies of prairie grouse that has experienced a significant decline in abundance and concurrent reduction in neutral genetic diversity. When examining the captive population for signs of inbreeding, variation in pedigree-based inbreeding coefficients (f(pedigree)) was less than that obtained from DNA-based methods (f(DNA)). Mortality of chicks and adults in captivity were also positively correlated with parental relatedness (r(DNA)) and f(DNA), respectively, while no correlation was observed with pedigree-based measures when controlling for additional variables such as age, breeding facility, gender and captive/release status. Further, individual homozygosity by loci (HL) and parental rDNA values were positively correlated with adult mortality in captivity and the occurrence of a lethal congenital defect in chicks, respectively, suggesting that inbreeding may be a contributing factor increasing the frequency of this condition among Attwater's Prairie-chickens. This study highlights the importance of using DNA-based methods to better inform management decisions when pedigrees are incomplete or errors may exist due to uncertainty in pairings.

Attacks on the endangered Attwater's Prairie-Chicken (Tympanuchus cupido attwateri) by black flies (Diptera: Simuliidae) infected with an avian blood parasite.

With fewer than 50 birds remaining in the wild, Attwater's Prairie-Chicken (Tympanuchus cupido attwateri) is critically endangered. Individuals of this species on the Attwater Prairie Chicken National Wildlife Refuge, Colorado Co., TX, have been attacked in successive winters, 2005-2006, by the blood-feeding black fly Cnephia ornithophilia. Attwater's Prairie-Chicken is a previously unreported host for Cnephia ornithophilia. Molecular screening indicated that about 15% of 13 blood-fed flies sampled from captured Attwater's Prairie-Chickens carried a parasite of the genus Leucocytozoon that can cause a debilitating avian malaria-like disease. If blood feeding or transmission of the disease agent becomes a threat to the birds, particularly in years of lean food supply or harsh weather, management of Cnephia ornithophilia should be considered.

Wild Birds, a Source of Reticuloendotheliosis Virus Infection for the Endangered Attwater's Prairie-Chicken ( Tympanuchus cupido attwateri)?

Reticuloendotheliosis virus (REV) infects a wide range of avian species. Since 1998, when it was first reported in a captive flock of the endangered Attwater's Prairie-chicken ( Tympanuchus cupido attwateri; APC), REV has plagued APC recovery efforts. While REV frequently occurs in captive bird flocks throughout the world, including commercial poultry, the reservoir for initial infection of flocks is poorly understood. From 2008-16, 412 blood samples and 216 liver samples collected from 32 species of birds on or near Attwater Prairie Chicken National Wildlife Refuge in Colorado County, Texas, US, and 89 blood samples obtained from a Texas game farm that provides thousands of Northern Bobwhites ( Colinus virginianus ) and Ring-necked Pheasants ( Phasianus colchicus ) for hunting throughout Texas, were tested for REV by real-time PCR. Of the 717 samples, one liver sample from a Savannah Sparrow ( Passerculus sandwichensis ) and three blood samples from game farm Ring-necked Pheasants tested positive for REV. These data, although limited, indicate a low prevalence of REV in birds sharing or in close proximity to APC habitat. More-extensive surveillance testing is warranted to determine the spatial and temporal dynamics of REV in wild bird populations and the relative role these birds may play as potential reservoirs for maintaining REV infections in both the wild and captive setting.

A duplex real-time polymerase chain reaction assay for the simultaneous detection of long terminal repeat regions and envelope protein gene sequences of Reticuloendotheliosis virus in avian blood samples.

The Reticuloendotheliosis virus (REV) group of retroviruses infects a wide range of avian species, including chickens, turkeys, ducks, geese, quail, and prairie chickens. The objective of the present study was to develop a highly sensitive and specific diagnostic test for the detection of REV in whole blood samples. In order to increase the diagnostic sensitivity, a duplex real-time polymerase chain reaction (PCR) that detects both the envelope protein gene (env) and the long terminal repeat (LTR) region of REV was designed. This assay demonstrated greater analytical and diagnostic sensitivity than the gel-based PCR assay when using DNA extracted from whole blood by both phenol-chloroform and magnetic bead methods. In general, threshold cycle values in the duplex real-time PCR assay were lower from DNA extracted using the magnetic bead system compared to DNA extracted by the phenol-chloroform method. Data presented herein show the successful development of a rapid and accurate test procedure, with high-throughput capability, for the diagnosis of REV infection using avian blood samples.