Immune responses amongst female zebras matured slowly while transitioning from nest-bound juveniles to adults, while those in males showed dramatic variation potentially due to the costs of moulting into their colourful sexually dimorphic plumage, a new study has revealed.
Evolutionary physiologists behind this research - Oliver Love, Katrina Salvante, James Dale, and Tony Williams - say that examined how a simple immune response varied at different life stages across the lifespan of individual zebra finches for their study, published in the September issue of the American Naturalist.
The researchers observed that adult males showed little variation in immune response despite changes in resource quality.
Immune responses among females, when they laid eggs under high-quality resource conditions, were also consistent with those during non-breeding and similar to male responses, say the researchers.
However, when laying on reduced resources, females reduced their immune response and their reproductive output consistent with a facultative (resource-driven) effect of reproductive effort on immunity.
The researchers further observed that even under high-resource conditions during the chick-rearing stage, mothers showed reduced immune responses compared to fathers, suggesting a residual energetic cost of egg-laying.
According to them, immune responses of juveniles of both sexes did not predict their subsequent adult responses.
Immune responses of adult females could be predicted only when the quality of the environment remained constant. As soon as conditions deteriorated, individual females required flexibility in both the immune and reproductive systems.
However, the degree of flexibility came at a cost as only individuals with high immune responses as non-breeders had the capacity to reduce responses when times became tough.
The researchers say that their findings indicate that immunity is a highly plastic trait that can be modulated in a sex- and context-dependent manner.
Given the need for individual flexibility in the immune system, this suggests that an immune response at one stage may provide limited information about immune response at future stages, they add.