Ostrich chick humoral immune responses and growth rate are predicted by parental immune responses and paternal colouration
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One of the most important measures of offspring performance is growth rate, which is often traded off against another important survival trait, immune function. A particular feature of ostrich chicks maintained in farmed environments is that cohorts of chicks vary widely in size. As parents can have a profound effect on the phenotype and fitness of their offspring, we investigated whether chick growth and immune defence were related to variation in levels of immune defence in their genetic parents. As secondary sexual traits of sires could serve as indicators of male quality, and be used in female mating decisions, we also investigated whether chick growth rate and immune defence were related to male plumage and integumentary colouration. We found that offspring growth rates and humoral responses were related to the humoral responses of their parents, suggesting that at least some components of humoral immune capacity are heritable. The white colour of male ostrich feathers was correlated to the humoral response and growth rate of their offspring, suggesting that this visual cue involved in the male courtship display could serve as an important signal to females of male quality, thereby forming the basis of mate choice in this species.
KeywordsStruthio camelus PHA injection Diphtheria Tetanus Plumage colouration Spectrophotometry Immunocompetence
We gratefully thank the National Research Foundation of South Africa for financial support, and the Western Cape Department of Agriculture for maintaining the research flock at the Oudtshoorn Research farm, and especially Stefan Engelbrecht and Basie Pfister for assistance in taking care of the birds and data collection. DH was supported by grants from the Swedish Research Council (VR), and partially from the Linnaeus excellence research project CAnMove financed by the Swedish Research Council and Lund University.
Ethical clearance for these experiments, which comply with the laws of South Africa, was granted by the Stellenbosch University ethics committee (2006B03001).
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