Polycyclic Aromatic Hydrocarbons Alter the Hepatic Expression of Genes Involved in Sanderling (Calidris alba) Pre-migratory Fueling

Comparison of gene expression and polycyclic aromatic compound profiles in hepatic tissue of black guillemot (Cepphus grylle) collected from an oil spill site and a non-spill site in the Arctic

Economic development, marine transportation, and oil exploration are all activities that are increasing in the Arctic region, and there is concern regarding increased oil-related contaminants entering this sensitive environment. Polycyclic aromatic compounds (PACs) are the main chemical constituents in oil-related contaminants and have been detected in wildlife species following both acute and chronic exposure. In 2020, an oil spill occurred in Kaikopok Bay near Postville, NL, Canada. In the present study, we evaluate hepatic PAC burdens and gene expression profiles, using a ToxChip PCR array, to determine key biological pathways most affected by exposure to an oil spill in a seabird species, black guillemot (Cepphus grylle). Black guillemots were also collected from a non-spill site at Nain, NL for chemical and gene expression analyses. We found distinct, diesel-related contaminant profiles in hepatic tissue of seabirds collected from the spill site, characterized by the presence of naphthalene congeners. Conversely, alkylated naphthalene congeners were more prevalent at the non-spill site. Although different chemistry profiles were detected between sites, gene expression profiles at the spill site were not as distinct as expected. However, using a regression modeling approach, the expression of certain target genes were good predictors of actual chemical concentrations. Overall, chemistry and gene expression used together can help support environmental monitoring initiatives in vulnerable species and geographic locations.

Contaminant biomonitoring augmented with a qPCR array indicates hepatic mRNA gene expression effects in wild-collected seabird embryos

Birds can bioaccumulate persistent contaminants, and maternal transfer to eggs may expose embryos to concentrations sufficient to cause adverse effects during sensitive early-life stages. However, using tissue residue concentrations alone to infer whether contaminant effects are occurring suffers from uncertainty, and efficient, sensitive biomarkers remain limited in wildlife. We studied relationships between whole embryo contaminant concentrations (total mercury, organochlorine pesticides, perfluoroalkyl substances, polychlorinated biphenyls, and halogenated flame retardants) together with mRNA expression in embryonic liver tissue from a Pacific Ocean seabird, the rhinoceros auklet (Cerorhinca monocerata). Fresh eggs were collected, incubated under controlled conditions, and from the pre-hatch embryo, hepatic RNA was extracted for qPCR array analysis to measure gene expression (2-∆Cq), while the remaining embryo was analyzed for contaminant residues. Contaminant and gene expression data were assessed with a combination of multivariate approaches and linear models. Results indicated correlations between embryonic total mercury and several genes such as sepp1, which encodes selenoprotein P. Correlation between the biotransformation gene cyp1a4 and the C7 perfluoroalkyl carboxylic acid PFHpA was also evident. This study demonstrates that egg collection from free-living populations for contaminant biomonitoring programs can relate chemical residues to in ovo mRNA gene expression effects in embryo hepatic tissue.

The effect of environmental pollution on gene expression of seabirds: A review

One of the biggest challenges for ecotoxicologists is to detect harmful effects of contaminants on individual organisms before they have caused significant harm to natural populations. One possible approach for discovering sub-lethal, negative health effects of pollutants is to study gene expression, to identify metabolic pathways and physiological processes affected by contaminants. Seabirds are essential components of ecosystems but highly threatened by environmental changes. Being at the top of the food chain and exhibiting a slow pace of life, they are highly exposed to contaminants and to their ultimate impacts on populations. Here we provide an overview of the currently available seabird-related gene expression studies in the context of environmental pollution. We show that studies conducted, so far, mainly focus on a small selection of xenobiotic metabolism genes, often using lethal sampling protocols, while the greater promise of gene expression studies for wild species may lie in non-invasive procedures focusing on a wider range of physiological processes. However, as whole genome approaches might still be too expensive for large-scale assessments, we also bring out the most promising candidate biomarker genes for future studies. Based on the biased geographical representativeness of the current literature, we suggest expanding studies to temperate and tropical latitudes and urban environments. Also, as links with fitness traits are very rare in the current literature, but would be highly relevant for regulatory purposes, we point to an urgent need for establishing long-term monitoring programs in seabirds that would link pollutant exposure and gene expression to fitness traits.

Improving hydrocarbon toxicity tolerance in poultry: role of genes and antioxidants

Sustenance of smallholder poultry production as an alternative source of food security and income is imperative in communities exposed to hydrocarbon pollution. Exposure to hydrocarbon pollutants causes disruption of homeostasis, thereby compromising the genetic potential of the birds. Oxidative stress-mediated dysfunction of the cellular membrane is a contributing factor in the mechanism of hydrocarbon toxicity. Epidemiological studies show that tolerance to hydrocarbon exposure may be caused by the activation of genes that control disease defense pathways like aryl hydrocarbon receptor (AhR) and nuclear factor erythroid 2p45-related factor 2 (Nrf2). Disparity in the mechanism and level of tolerance to hydrocarbon fragments among species may exist and may result in variations in gene expression within individuals of the same species upon exposure. Genomic variability is critical for adaptation and serves as a survival mechanism in response to environmental pollutants. Understanding the interplay of diverse genetic mechanisms in relation to environmental influences is important for exploiting the differences in various genetic variants. Protection against pollutant-induced physiological responses using dietary antioxidants can mitigate homeostasis disruptions. Such intervention may initiate epigenetic modulation relevant to gene expression of hydrocarbon tolerance, enhancing productivity, and possibly future development of hydrocarbon-tolerant breeds.

Review of contaminant levels and effects in shorebirds: Knowledge gaps and conservation priorities

Environmental pollution has emerged as a major threat to bird populations. Many shorebird populations are declining, although contamination has been documented in some shorebirds, evidence of negative impacts is sparse and this important topic remains understudied. To guide future research and develop effective conservation strategies, we carried out a comprehensive review of environmental pollutants and their consequences on shorebirds. In total, we found 93 relevant articles which examined pollutant contamination in ~37% (79 of 215) of all shorebird species, mostly from the Charadriidae and Scolopacidae families. Studies were geographically biased: the majority were conducted in American flyways, while only 1 was found from Australasia and few were conducted in Asian flyways. The main geographic gap for research includes East Africa, South Asia and Siberian Arctic. The most well-documented pollutants included mercury (Hg, 37 studies), cadmium (33), and lead (Pb, 28); less well studied pollutants were barium (1), calcium (1), strontium (1), dicofols (1), and other newly emerging contaminants, such as plastic debris/microplastics (4) and antibiotics resistance (2). Several pollutants have caused considerable concerns in shorebirds, including embryotoxicity caused by PCBs at non-optimum temperature (laboratory experiments); reduced reproduction performance linked to maternal Hg and paternal Pb (field evidence); and reduced refueling and flight performance related to oil contamination (both field and laboratory evidence). Our results confirm that an in-depth understanding of the local, regional and global factors that influence population trends of shorebirds in light of increasing pollution threats is essential for accurate and effective management and conservation strategies.