The Interactive Effects of Incubation Temperature and Organic Contaminants on Shorebird Embryo Development

Abstract

Understanding the effects of multiple, possibly interactive, stressors on wildlife is an emerging issue in ecotoxicology. In particular, how changes in temperature will alter organisms’ responses to chemical contaminants may be of particular concern for arctic-breeding shorebird populations, which have declined in recent decades, concomitant with changes in spring temperatures and continued long-range transport and release of persistent organic pollutants (POPs). During incubation, for example, changes in temperature and exposure to environmental contaminants can both negatively affect avian development and may have interactive effects on the embryo that are more detrimental than either effect individually (cumulative effects hypothesis). Specifically, incubation temperature may influence the rate of development and how contaminants are metabolized, resulting in potentially multiplicative effects on embryo growth and development. To test the cumulative effects hypothesis and assess contaminant and temperature conditions during incubation, I conducted captive (Chapter 2) and field studies (Chapter 3) using shorebirds as model organisms. In the former, I conducted a controlled egg injection and incubation study on wild killdeer (Charadrius vociferous) eggs exposed to concentrations of a known endocrine disruptor, PCB-126 (0, 44 or 89 ng/g) and incubated at either low (36°C), intermediate (37.5°C), or high (39°C) temperatures. In the latter study, I analyzed POPs in semipalmated sandpiper (Calidris pusilla) eggs from three arctic sites and examined relationships between egg POPs, ambient temperature, nest-cup temperature, and chick measures at hatch. My captive study results showed the most severe effects (yolk distention, first detection of heartbeat and incubation length, righting reflex) in birds incubated under suboptimal low or high incubation temperatures combined with high PCB-126 exposure, indicating that shorebird embryos may be more tolerant of contaminant exposure under intermediate temperatures. Field results indicated relatively low ubiquitous levels of POPs – namely organochlorines (mean ± standard deviation, 29.33 ± 37.08 ng/g), brominated flame retardants (2.44 ± 6.56 ng/g), and polychlorinated biphenyls (26.59 ± 54.25 ng/g) –in semipalmated sandpiper eggs. At the nest level, incubation temperature was positively correlated with ambient temperature, suggesting incubating adults cannot fully buffer the effects of temperature fluctuations and embryos may be susceptible to suboptimal incubation temperatures. Collectively, these findings suggest that changing arctic conditions that alter spring temperatures and release of historical POPs can interact to affect avian development with potential consequences for reduced fitness.