Parasites, morphology, and blood characters in male Red Jungle Fowl during development

Parasites have significant effects on the fitness of their hosts. We used an intestinal nematode, Ascaridia galli, as an experimental treatment of young male Red Jungle Fowl (Galius gallus) to investigate the effect of this parasite on their growth and development through sexual maturity. After treatment, 26% of those fed parasites and 31% of controls became infected. Infected males had lower body mass, lower hematocrit, a higher percentage of lymphocytes among their white blood cells, and smaller combs than uninfected males. Infected and uninfected males did not differ in plasma levels of testosterone (T). The differences between parasitized and unparasitized males persisted from 5 months of age through sexual maturity. The classic example of hormonal action is the effect of testosterone on the comb of male chickens, but the difference in comb length between parasitized and unparasitized male Red Jungle Fowl along with no difference in T suggests that the effect of parasites on male secondary sexual characters does not necessarily involve a change in circulating levels of testosterone.