First documentation of malaria parasites (genus Plasmodium) in the Saltmarsh Sparrow (Ammodramus caudacutus) and patterns of infection with mercury exposure

Avian malaria parasites, protist parasites of the genus Plasmodium, are extremely common in birds worldwide and have the ability to dramatically impact sensitive populations and species. Mercury, a heavy metal that accumulates in the tissues of birds, is a common environmental pollutant that may reduce immune system function and increase susceptibility to malaria parasite infection. I surveyed the endangered Saltmarsh Sparrow (Ammodramus caudacutus), a species with high exposure to mercury, for malaria parasites. Specifically, I investigated the presence, diversity, and distribution of malaria parasites in the species, the degree of sharing of parasite lineages with other bird species, and the relationship between blood mercury levels and infection status. Through collaboration with researchers at the Biodiversity Research Institute (BRI) and the University of New Hampshire (UNH), blood samples were collected from 290 individuals across the entire breeding range of the species from Maine to Maryland, U.S. By sensitive nested PCR methods, I screened each sample for malaria parasite infection and each positive infection was sequenced at the mitochondrial cytochrome b gene to identify parasite lineages, the standard gene used in defining Plasmodium lineages. Overall, 16.5% of Saltmarsh Sparrows were found to be infected with a total of six Plasmodium lineages. Prevalence and diversity of parasite lineages varied across the breeding range of the Saltmarsh Sparrow, with greater prevalence and diversity in northern states. The skewed distribution of prevalence and parasite diversity may be due to mosquito control measures, habitat type, or possibly climate change. All six parasite lineages were found to be shared with other passerine species including those also found to nest in or near saltmarshes. Blood mercury levels varied in the Saltmarsh Sparrow, ranging from 0.18 ppm to 2.52 ppm with a mean of 0.86 ppm. Although a positive correlation was expected between blood mercury levels and infection status because mercury negatively impacts an individual’s ability to fight infection, I found a negative correlation. These results suggest that individuals with low blood mercury levels are more likely to be infected with malaria parasites. The discovery of a relatively high prevalence and diversity of malaria parasites in the Saltmarsh Sparrow, a species in rapid decline across its range, and the negative correlation relationship between mercury exposure and malaria parasite infection status, suggest the need for continued study of malaria parasite dynamics in the species. Further research will help elucidate the link between environmental pollution and infectious disease risk, which is a pressing topic as environmental contamination combined with climate change may heavily impact host, vector, and parasite distributions and host-parasite dynamics

Songbirds as sentinels of mercury in terrestrial habitats of eastern North America

Mercury (Hg) is a globally distributed environmental contaminant with a variety of deleterious effects in fish, wildlife, and humans. Breeding songbirds may be useful sentinels for Hg across diverse habitats because they can be effectively sampled, have well-defined and small territories, and can integrate pollutant exposure over time and space. We analyzed blood total Hg concentrations from 8,446 individuals of 102 species of songbirds, sampled on their breeding territories across 161 sites in eastern North America [geometric mean Hg concentration = 0.25 μg/g wet weight (ww), range < 0.01–14.60 μg/g ww]. Our records span an important time period—the decade leading up to implementation of the USEPA Mercury and Air Toxics Standards, which will reduce Hg emissions from coal-fired power plants by over 90%. Mixed-effects modeling indicated that habitat, foraging guild, and age were important predictors of blood Hg concentrations across species and sites. Blood Hg concentrations in adult invertebrate-eating songbirds were consistently higher in wetland habitats (freshwater or estuarine) than upland forests. Generally, adults exhibited higher blood Hg concentrations than juveniles within each habitat type. We used model results to examine species-specific differences in blood Hg concentrations during this time period, identifying potential Hg sentinels in each region and habitat type. Our results present the most comprehensive assessment of blood Hg concentrations in eastern songbirds to date, and thereby provide a valuable framework for designing and evaluating risk assessment schemes using sentinel songbird species in the time after implementation of the new atmospheric Hg standards.Keywords: Songbird, Sentinel, Bioaccumulation, Mercury, Passeriforme

A Noncoding Point Mutation of Zeb1 Causes Multiple Developmental Malformations and Obesity in Twirler Mice

Heterozygous Twirler (Tw) mice develop obesity and circling behavior associated with malformations of the inner ear, whereas homozygous Tw mice have cleft palate and die shortly after birth. Zeb1 is a zinc finger protein that contributes to mesenchymal cell fate by repression of genes whose expression defines epithelial cell identity. This developmental pathway is disrupted in inner ears of Tw/Tw mice. The purpose of our study was to comprehensively characterize the Twirler phenotype and to identify the causative mutation. The Tw/+ inner ear phenotype includes irregularities of the semicircular canals, abnormal utricular otoconia, a shortened cochlear duct, and hearing loss, whereas Tw/Tw ears are severely malformed with barely recognizable anatomy. Tw/+ mice have obesity associated with insulin-resistance and have lymphoid organ hypoplasia. We identified a noncoding nucleotide substitution, c.58+181G>A, in the first intron of the Tw allele of Zeb1 (Zeb1Tw). A knockin mouse model of c.58+181G>A recapitulated the Tw phenotype, whereas a wild-type knockin control did not, confirming the mutation as pathogenic. c.58+181G>A does not affect splicing but disrupts a predicted site for Myb protein binding, which we confirmed in vitro. In comparison, homozygosity for a targeted deletion of exon 1 of mouse Zeb1, Zeb1ΔEx1, is associated with a subtle abnormality of the lateral semicircular canal that is different than those in Tw mice. Expression analyses of E13.5 Twirler and Zeb1ΔEx1 ears confirm that Zeb1ΔEx1 is a null allele, whereas Zeb1Tw RNA is expressed at increased levels in comparison to wild-type Zeb1. We conclude that a noncoding point mutation of Zeb1 acts via a gain-of-function to disrupt regulation of Zeb1Tw expression, epithelial-mesenchymal cell fate or interactions, and structural development of the inner ear in Twirler mice. This is a novel mechanism underlying disorders of hearing or balance

Pilot Assessment of Mercury Exposure in Selected Biota from the Lowlands of Nicaragua = Evaluación Piloto de Exposición al Mercurio en Biota Selecta de las Tierras Bajas de Nicaragua

Abstract. Methylmercury, a potent neurotoxin, can damage health of humans and wildlife. In 2012, we collected 73 blood and feather samples from birds among diverse foraging guilds to assess mercury exposure in wetland habitats associated with Lakes Managua and Nicaragua. Blood levels (0.72 parts per million) in a piscivorous Neotropic Cormorant Phalacrocorax brasilianus from Lake Managua exceeded the United States Environmental Protection Agency recommended screening value for fish consumption of 0.3 ppm. Cormorants should be considered as an upper trophic level bioindicator of aquatic Hg toxicity. Of all the wetland invectivorous birds sampled, Northern Jaçana Jacana spinosa had the highest blood mercury concentrations (0.42 ppm) and we consider it as a bioindicator of wetland contaminants. Four of five species exhibiting the highest levels of blood mercury were piscivores and ground foraging invertivores. Several neotropical migrants exceeded feather concentration of >3.0 ppm and are considered at greater risk to reduced reproductive success.-- Resumen. Los efectos del metilmercurio (MeHg) en seres humanos y vida silvestre a nivel neurológico y reproductivo ha sido poco documentado en el neotrópico. En Febrero de 2012 se colectaron 73 muestras de sangre y plumas en 92 aves de distintos gremios alimenticios (piscívoros, omnívoros, insectívoros). Se encontraron niveles mayores (0.3 partes por millón) a los permitidos por la Agencia para la Protección Ambiental en Norteamérica en Phalacrocorax brasilianus (0.72 ppm). Esta ave puede considerarse un buen bioindicador del medio ambiente. De todas las especies muestreadas las concentraciones de mercurio más altas fueron de Jacana spinosa (0.42 ppm). Aves paserinas capturadas que registraron niveles de mercurio en los rectrices >3.0 ppm pueden mostrar bajo éxito reproductivo

Mercury exposure to red-winged blackbirds (Agelaius phoeniceus) and dragonfly (Odonata: Aeshnidae) nymphs in Prairie Pothole wetlands

The Prairie Pothole Region (PPR) in the northern Great Plains is an area of ecological significance, serving as an important breeding site for avian wildlife. However, organisms feeding within the PPR may be at risk of mercury (Hg) exposure due to deposition of anthropogenic emissions and the high Hg methylation potential of PPR wetlands. We quantified Hg concentrations in red-winged blackbirds’ (Agelaius phoeniceus (Linnaeus, 1766); RWBLs) blood, feathers, and eggs in the spring and summer breeding season and compared our values with those from RWBLs sampled from ecoregions across North America. Hg concentrations in whole water, aeshnid dragonfly nymphs, and RWBL tissues varied by wetland and were below those considered to elicit acute effects in wildlife, and egg total Hg (THg) concentrations were significantly related to spring whole water methylmercury concentrations. Only RWBL blood THg concentrations showed a clear increase in summer compared with spring, resulting in decoupling of summer blood and feather THg concentrations. Moreover, blood THg concentrations varied by ecoregion, with those impacted by an industrial point source exhibiting high Hg levels. Our study emphasizes that tissue renewal time as well as ecological factors such as competition and diet shifts are important considerations when using RWBLs to assess biological Hg exposure

The corticosterone stress response and mercury contamination in free-living tree swallows, Tachycineta bicolor

Abstract We determined mercury concentrations in tree swallows, Tachycineta bicolor, from Massachusetts and Maine with different levels of contamination. Baseline and stress-induced plasma corticosterone concentrations from adults and nestlings (Massachusetts only) were compared with mercury concentrations. In Massachusetts, adult baseline corticosterone was negatively correlated with blood mercury, but showed a nearly-significant positive correlation with feather mercury. There was a negative relationship between baseline corticosterone and blood mercury in nestlings and between baseline corticosterone and egg mercury. There was no relationship between mercury and stress-induced corticosterone in any of the groups, or with baseline corticosterone in Maine sites where mercury levels were lower. The findings suggest blood and egg mercury may be a better indicator of current condition than feather mercury. Further, mercury contamination may not alter stress-induced corticosterone concentrations in tree swallows but appears to have a significant impact on baseline circulating corticosterone

Mercury in breeding saltmarsh sparrows (Ammodramus caudacutus caudacutus).

Abstract Environmental mercury exposure of birds through atmospheric deposition and watershed point-source contamination is an issue of increasing concern globally. The saltmarsh sparrow (Ammodramus caudacutus) is of high conservation concern throughout its range and the potential threat of mercury exposure adds to other anthropogenic stressors, including sea level rise. To assess methylmercury exposure we sampled blood of the northern nominal subspecies of saltmarsh sparrows (A. c. caudacutus) nesting in 21 tidal marshes throughout most of the species\u27 breeding range. Blood of tree swallows (Tachycineta bicolor) was sampled concurrently at three of these sites to provide a comparison with a well-studied songbird that is a model species in ecotoxicology. Arithmetic means (±1 SD) ranged from 0.24 ± 0.06 μg g -1 wet weight (ww) in Connecticut to 1.80 ± 0.14 μg g -1 ww in Massachusetts, differing significantly among sites. Comparison to tree swallows indicates that mercury exposure is significantly higher in saltmarsh sparrows, making them a more appropriate bioindicator for assessing risk to methylmercury toxicity in tidal marsh ecosystems