The effects of parental age on growth and cell-mediated immune response of chicks of Zebra finch, Taeniopygia guttata

Abstract

The reproductive performance of birds tends to increase with age until they reach reproductive senescence. The age of a nesting pair may affect their offspring, because the quantities of substances transferred through egg yolk and the food they provide their nestlings may decline as they age. Reduced parental care may adversely affect the development of the offspring. Consequently, the present study focused on investigating the effect of parental age on the growth and cell-mediated immunity in chicks of the Zebra Finch (Taeniopygiaguttata). I hypothesised that high parental age would lead to increased growth and reduced cell-mediated immune response, and also that the sex of the offspring would have an effect ontheir growth and immunocompetence.

The experiment was conducted on broods from two parental age groups of Zebra finches, young (one year old) and old (three to four years old). Clutch size, egg mass and hatching were monitored daily. Growth curves were plotted from daily measurements of nestling bodymass, from zero to 16 days of age. Quantification of the cell-mediated immune response of the nestlings was done using the phytohaemagglutinin skin-test at 15 days of age.

The results showed that the asymptotic body mass was strongly affected by parental age, with the chicks of young parents having higher asymptotic body mass than those of old parents.However, no difference was observed in the growth rates of the chicks from the two parentalage groups. I have suggested, since nestlings in both age groups had the same growth rate,that the difference in asymptotic body mass may be ascribed to an initial difference inhatchling body mass. Parental age did not affect the cellular immune response of the chicks. I found that old parents seemed to prioritize male nestlings, while young parents prioritizedfemale nestlings. This was reflected in both the growth and cellular immune response of thechicks. I have suggested that nesting parents prioritize the sex most likely to survive to are productive age.