Insight on trace element detoxification in the Black-tailed Godwit (Limosa limosa) through genetic, enzymatic and metallothionein analyses

Abstract

Trace element concentrations (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, Zn) were investigated in the liver, kidneys, muscle and feathers of 31 black-tailed godwits (Limosa limosa) accidentally killed during catches by mist net in the Pertuis Charentais, Atlantic coast of France. Analyses of carbon and nitrogen stable isotope ratios were carried out in liver, muscle and feathers in order to elucidate dietary patterns and to determine whether differences in diet explained the variation in elemental uptake. This study also aimed to have a preliminary assessment of sub-lethal effects triggered by trace elements through the investigation of gene expressions by quantitative real-time PCR, antioxidant enzyme activities (catalase, superoxide dismutase, glutathione peroxidase), and metallothionein (MT) levels. The results showed that Cr and Ni concentrations in tissues of adults were lower than in juveniles in part because adults may have eliminated these trace elements through moulting. Except for Cd and Ni, trace element concentrations were negatively correlated to the body mass of godwits. Ag, As, Hg and Se concentrations were positively linked with the trophic position of birds. The diet could be considered as a fundamental route of exposure for these elements demonstrating therefore the qualitative linkage between dietary habits of godwits and their contaminant concentrations. Our results strongly suggest that even though trace element concentrations were mostly below toxicity threshold level, the elevated concentrations of As, Ag, Cd, Cu, Fe and Se may however trigger sub-lethal effects. Trace elements appear to enhance expression of genes involved in oxidative stress defence, which indicates the production of reactive oxygen species. Moreover, birds with the highest concentrations appeared to have an increased mitochondrial metabolism suggesting that the fight against trace element toxicity requires additional energetic needs notably to produce detoxification mechanisms such as metallothioneins.

Evidence of species-specific detoxification processes for trace elements in shorebirds

“…Relative gene expression levels were normalized according to b-actin gene expression which was stable across tissues and samples. Induction and repression factors were calculated between the Red Knot and the Black-tailed Godwit (Lucia et al 2012) following the formula: 2 (-DCT BQN) /2 (-DCT RK) , where DCT is the Threshold Cycle of the Black-tailed Godwit (BTG) and the Red Knot (RK) normalized according to their respective b-actin CT.…”

“…Glutathione peroxidase (GPx) activity was determined in the liver of Red Knots according to the method of Paglia and Valentine (1967) using a GPx assay kit (RS504/RS505, RANDOX, France) as previously described (Lucia et al 2012).…”

“…Hepatic superoxide dismutase (SOD) and catalase activities were determined according to the methods of Wooliams et al (1983) and Deisseroth and Dounce (1970), respectively, using assay kits (SD125, RANDOX, France and CAT100, Sigma-Aldrich, USA) as previously described (Lucia et al 2012). The results are presented in units of SOD or catalase per mg of protein.…”

“…Filling in these gaps in the data is crucial for these endangered species. Yet, a previous study on the Black-tailed Godwit (Limosa limosa) from the Pertuis Charentais demonstrated possible production of reactive oxygen species, and suggested that in order to counter trace element toxicity, additional energy needs are required, especially to sustain detoxification mechanisms (Lucia et al 2012). However, even though Red Knots and Godwits are both specialized to feed on mudflats, their morphology and feeding behaviours are different.…”

“…The objective of the current study was to compare the detoxification processes and sub-lethal effects of trace elements in free-ranging Red Knots to previous results obtained on Black-tailed Godwits (Lucia et al 2012) wintering or staging in the Pertuis Charentais. The concentrations of the 13 trace elements cited above were determined in the liver, kidneys, muscle and feathers of Red Knots.…”