The emission of heavy metals in the environment is often accompanied by emissions of acidifying pollutants. The acidification of terrestrial ecosystems results in the leaching of calcium and consequently a lowered concentration or availability of this essential nutrient in the environment. Calcium deficiency in the diet may lead to an increased absorption of toxic metals. In this study we investigated the effect of calcium availability on the accumulation of lead and essential metals (calcium, copper, iron and zinc) in important target tissues of zebra finches (Taeniopygia guttata). When exposed to 20 ppm lead via drinking water, zebra finches excluded from an additional calcium supply (i.e. oyster shell grit) accumulated significantly higher concentrations of lead in liver, kidney, muscle, brain and bone than zebra finches with access to oyster shell grit. Levels of calcium, copper, iron and zinc were not significantly affected by either the calcium availability or the increased absorption of lead. There were no significant sex related differences, suggesting that males and females have a similar demand, metabolism and/or distribution of calcium and other metals in the non-reproductive period. This study clearly illustrates the importance of calcium supply on the bioavailability of lead.
The typical costs associated with parasitism have led to the suggestion that immunosuppression in the host may be an important mechanism mediating the life history cost of reproduction, defined as a decrease in residual reproductive value as a consequence of parental effort. More immunocompetent individuals have therefore been predicted to reveal higher fitness through more optimal reproductive decisions and increased survival. In this study, we simulated a challenge to the immune system of male and female great tits (Parus major) by injecting a novel but harmless antigen, sheep red blood cells (SRBC), and related the elicited immune response to (long-term) survival and reproductive traits, relevant to the determination of lifetime reproductive success in this species. In females, we could not detect any relationships between humoral immunocompetence and laying date, clutch size, or mean fledging mass during the breeding season following the winter period during which we assessed the immune response. Furthermore, immune response to SRBC did not predict survival of male and female great tits until the following breeding season as well as until the breeding season the year after. Overall, humoral immunological quality measured during winter did not predict important fitness components in great tits.
Measuring the primary antibody immune response to an injection with sheep red blood cells (SRBC) is a routine application in poultry science. Recently, this technique is also becoming an increasingly popular tool to investigate humoral immunocompetence in free-living birds in studies of ecological immunology and immunotoxicology. However, an extensive search of the literature revealed that many of these studies have been measuring the primary immune response to SRBC without verifying first when maximum levels of antibodies are reached in the bird species under study. In addition, most studies assessed antibody titres to SRBC approximately 6 days after their inoculation assuming a similar pattern as found in poultry. We tested this assumption of a uniform pattern of kinetics of the primary humoral immune response to SRBC across bird species and investigated it in detail in two important model species, namely the great tit Parus major and the European starling Sturnus vulgaris. In general, the pattern was found to be the same in both passerine species and strongly resembled the pattern observed in chickens. Maximum antibody levels (the plateau phase) were reached on, respectively, day 5 and day 6 (with day of inoculation = day 0) of the immune response in the great tit and the starling and lasted for 3 days in both species. We found no effects of age, sex or time spent in captivity. Furthermore, our findings suggest that antibody levels to SRBC should not be obligatory assessed during the plateau phase of maximum antibody levels although it still remains most accurate to do so or at least shortly before or after it. Overall, we conclude that antibody levels have been reliably assessed in most avian studies using this technique.