Biological responses to environmental contamination. How can metal pollution impact signal honesty in avian species?

Abstract

Environmental pollution, for example with metals, can significantly affect the ecosystem balance leading to severe changes. Biologically active pigments are relevant for the appearance and condition of birds. Melanin and carotenoid particles are the most frequently deposited pigments in avian integument. They are responsible for the majority of colors of bird plumage. The phenotypic expression can be affected by metal contamination. It can be manifested as color bleaching or differences in the size of plumage badges. In this study, we performed a comprehensive review of related studies in order to estimate the underlying population effect of this potential dependency. The study is based on the review of the literature regarding several avian species. It was designed to identify an area where the effect of the exposure is still poorly known. The analysis was specifically conducted to investigate the correlation between trace element concentration and eumelanin deposition. Moreover, we searched for factors that could affect spectral properties of feathers with carotenoid‐based pigmentation. As a result, we found carotenoid‐based pigmentation to be of a good use in terms of visual condition assessment. Changes in melanin‐based pattern should be analyzed separately for eu‐ and pheomelanin as well as for a range of essential and toxic elements. Comprehensive studies on the subject are still scarce. Therefore, the issue requires further investigation.

Decoding the Evolution of Melanin in Vertebrates

“…Melanin has important, but relatively understudied, functions in immunity, including antimicrobial and antipathogen functions [44] and metal homeostasis [10]. In extant birds [45] and the seasnake Emydocephalus [46], integumentary melanins can bind environmentally derived metal ions (e.g., Ca 2+ , Fe 3+ , Cu 2+ , Zn 2+ , Cd 2+ , and Pb 2+ ) that may be excreted via accelerated sloughing [46]. These melanosome-associated metals may represent physiologically important redox-active metals that can be released when needed [47,48], or excess metals derived from metabolic processes (or the external environment) that are isolated from active metabolism, as in hair and feathers [45,46].…”

Ingested plastic and trace element concentrations in Short-tailed Shearwaters (Ardenna tenuirostris)

“…Elevated trace element concentrations in birds has direct, and indirect health impacts, such as liver and kidney damage (e.g. Cd; Hoffman et al, 2011;Nicholson and Osborn, 1983;Salamat et al, 2014), reduced survival (Goutte et al, 2015), and changes in feather pigmentation (Pacyna et al, 2018).…”

Animal Coloration in the Anthropocene

“…As previously established here, color displays that act as honest indicators of quality can be heavily constrained by diet and nutritional deficiencies in their respective environments. Broadly, polluting compounds impact animal coloration through multiple pathways: by inhibiting or disrupting the acquisition of carotenoid precursors, by replacing similar compounds in key biochemical pathways and by causing general declines in overall health and condition (Pacyna et al, 2018). The abundance of literature (Table 1) on the effects of pollutants on plumage coloration in birds suggests that carotenoid-based coloration could be used as an indicator of pollution.…”