Clinal variation in the polymorphic Black Sparrowhawk Accipiter melanoleucus is unrelated to infection by the blood parasite Haemoproteus nisi

• Published in: Journal of ornithology 2021, Vol.162 (1), p.231-241
• Main Authors: McCarren, Sam, Sumasgutner, Petra, Tate, Gareth, Koeslag, Ann, Amar, Arjun
• Format: Article
• Language: English
• Subjects: Accipiter melanoleucus; Biomedical and Life Sciences; Blood parasites; Breeding seasons; Ecology; Fish & Wildlife Biology & Management; Haemoproteus nisi; Hypotheses; Infections; Invertebrates; Life Sciences; Melanocortin; Original Article; Parasite resistance; Parasites; Rainfall; Rainfall levels; Reproductive fitness; Seasons; Vectors; Zoology
• ISSN: 2193-7192; 2193-7206
• DOI: 10.1007/s10336-020-01823-3

Blood parasites can impact host fitness and can, thus, act as selective agents in their host’s evolution. The melanocortin system linked to colouration of vertebrates may infer higher parasite resistance via pleiotropic properties of the genes involved. Black Sparrowhawks ( Accipiter melanoleucus ) are colour polymorphic (dark and light morph adults) and distributed clinally in South Africa, with more dark morphs in the Southwest where the breeding season coincides with the rainy season. There, dark morphs have lower infections of haemosporidian parasites Haemoproteus nisi , suggesting a higher parasitic resistance. Thus, it is hypothesized that the morph distribution may be an adaptive response to coping with varying parasite prevalence associated with rainfall levels, which may regulate the parasites’ invertebrate vectors. This hypothesis assumes a fitness cost of high parasite burden, which could be specifically important during the energy-demanding breeding season. To explore this, we (1) quantified Black Sparrowhawk H. nisi infections across South Africa, and explored (2) breeding performance and apparent annual survival of adults, and (3) nestling body condition in Cape Town in relation to infection levels. In contrast to the predictions, we found that parasite prevalence did not vary across the country, we found no fitness costs of higher infection levels for breeding birds, and also nestling body condition was independent of infection levels. Thus, we found no support for our hypothesis. Black Sparrowhawk polymorphism is unlikely to be driven by an adaptive function linked to dealing with higher infections with H. nisi in regions with wetter breeding seasons.