Lead exposure positively affects coccidia abundance in feral pigeons (Columba livia)

Abstract

O_LIIn urban environments, organisms are exposed to high levels of pollutants, including trace metals, whose concentrations can be increased by anthropogenic activities. Numerous studies have shown the toxic effects of pollutants on exposed organisms. However, due to their life within the host, parasites can also be affected by exposure to these pollutants. Overall, previous correlative findings reveal that the effects of parasite exposure to pollutants through the host can vary, from positive to negative, highlighting the complexity of host-parasite-environment interactions in relation to pollution. C_LIO_LIIn this study, we experimentally tested whether lead exposure affects the abundance of ecto-, meso-, and endoparasites in wild pigeons (Columba livia), which host a wide variety of parasites and are naturally exposed to trace metals in urban environments. As we had previously reported the toxic effects of lead on the immune system of pigeons, we expected lead exposure to be indirectly beneficial for the parasites. C_LIO_LITo test this, we used a sample of wild pigeons captured in Paris, half of which were experimentally exposed to lead concentrations similar to those found in Paris. We then measured the abundance of several parasites: blood parasites (hemosporidian parasites), ectoparasites (Columbicola columbae and Campanulote compar), coccidia and helminths. Additionally, we measured the intensity of the pigeons antiparasitic behavioral response (grooming) through behavioral analyses. C_LIO_LIOur results did not reveal toxic effects of lead exposure on the parasites. On the contrary, we found positive effects of this exposure on coccidia abundance in male pigeons. This result could be explained by a toxic effect of lead on the hosts antiparasitic immune strategy, making the hosts less hostile to parasites. However, we found no effect of lead exposure on the abundance of lice, blood parasites and helminths. This could be explained by the lack of impact of lead exposure on grooming antiparasitic activity in our experiment, and by seasonal variations in the activity of blood parasite vectors, which may have masked potential effects of our treatment. C_LIO_LIIn conclusion, our study highlights the importance of considering the host environment, particularly pollutants, to understand parasite dynamics. C_LI