Carotenoids in the seminal fluid of wild birds: Interspecific variation in fairy-wrens

Male secondary sexual characters can provide females with information regarding the fertilizing capacity of a male's sperm. In some fishes and birds, intense nuptial coloration is correlated with male fertilizing capacity, but no mechanistic link between coloration and sperm quality has been established. One plausible mechanism is that carotenoid pigments, which color skin and feathers in many animals, are present in seminal fluid and serve as antioxidant protectors of sperm. We used high-performance liquid chromatography (HPLC) to analyze sperm samples from four species of Australian fairy-wren (Malurus) and detected low concentrations (<1 μg ml^-1) of carotenoids in some samples. Xanthophyll carotenoids (including lutein and zeaxanthin), which are typically dietary in origin, were present in the seminal fluid of Superb (M. cyaneus) and Splendid (M. splendens) Fairy-Wrens. In contrast, red ketocarotenoids (including astaxanthin and canthaxanthin), which are likely metabolically derived from dietary precursors, were present in the seminal fluid of Red-backed Fairy-Wrens (M. melanocephalus). This work is the first to report carotenoids in avian seminal fluid and suggests that, although carotenoids are at low levels and thus may have limited antioxidant activity, there may be biological variability in avian semen carotenoids on which selection could act.