Incubation temperature and PCB-126 exposure interactively impair shorebird embryo and post-hatch development

In oviparous wildlife, many critical physiological and behavioural components are strongly influenced by the embryonic and early post-hatch developmental environment. As such, early life stages in these species are highly vulnerable to both natural and anthropogenic stressors. For example, in birds, incubation temperature may influence the rate of egg development while also affecting contaminant metabolism and absorption in body tissues, resulting in potentially multiplicative impacts on embryonic and posthatch development. We tested the hypothesis that cumulative effects of early contaminant exposure and temperature stress can negatively affect avian development and may have interactive effects that are more detrimental than either stressor individually. Using a controlled egg injection and incubation study on killdeer (Charadrius vociferous), eggs were exposed to a known endocrine disruptor, 3,3',4,4',5-pentachlorobiphenyl (PCB-126) and incubated at either low (36 °C), intermediate (37.5 °C), or high (39 °C) temperatures. Our results indicated that eggs incubated at low temperature had earlier detection of heartbeat, longer incubation length, lower growth rate post-hatch, and higher post-hatch mortality, compared to eggs incubated under intermediate temperatures. Higher incubation temperatures resulted in shorter incubation length, earlier detection of heart rate and faster righting time. As predicted, embryo and chick mortality were greater in the PCB-dosed birds incubated at intermediate and high temperatures. Incidence of distended yolk sacs (%) also increased with PCB exposure in all temperature groups, with the largest increase in the high temperature group. Overall, our results show that low incubation temperature can cause greater adverse effects than PCB-126 exposure alone, but that negative effects of PCB-126 exposure are exacerbated by high incubation temperatures. These findings suggest that in natural settings, shorebird embryos may be more susceptible to contaminant exposure when incubated at temperatures either below or above the apparent optimum.