In a previous News post we presented a long-term experiment in which infestation by an intestinal unicellular parasite (Isospora coccidian) was manipulated in a group of house sparrows (medicated with anticoccidial drug), while another group served as control (not medicated, infestation level similar to natural levels). The experiment lasted 15 months and so covered two moulting periods and more than a whole annual cycle. We found differences between groups in several feather quality variables, while moult schedule was independent of treatment.

In an accompanying study we asked whether different physiological measures (immune system and redox state) show annual cycling and whether this annual is governed by coccidian infestation. We found significant variation in 10 out of 12 traits over the year. However, we found little support for the parasite-mediated change in immune functions and oxidative status in captive house sparrows. Of the 12 measures, only one was slightly affected by the parasite treatment. In support of the absence of any effect of coccidians on the annual profile of the condition and physiological traits, we found no consistent relationships between the intensity of infestation and these response variables over the year. Our results show that chronic coccidian infections have limited effect on the seasonal changing of physiological traits, and that the patterns of these measures are probably more affected by acute infection and/or by virulent parasite strains. We submitted the manuscript in Physiological and Biochemical Zoology, where, based on the positive feedback by two reviewers, was provisionally accepted (minor revision).

The study was financed by a CNCSIS research grant (PN II. RU TE 291/2010).

Pap PL, Sesarman A, Vágási CI, Buehler DM, Pătraș L, Versteegh MA and Banciu M 2014. No Evidence for Parasitism-linked Changes in Immune Function or Oxidative Physiology over the Annual Cycle of an Avian Species.