Ecologia da interação parasito-hospedeiro: efeitos da malária sobre a coloração de carotenoides na plumagem e condição corporal de aves em área de Cerrado

Abstract

Malaria parasites and birds have been a model study system of parasite-host interaction, being one of the reasons the parasite collection can be performed without causing damage to the host population. Chronic infections, with low parasitemia, can cause damage to the hosts, since it would be allocated a greater amount of resources (energy) to the immune system, reducing body mass. The body condition index is used to characterize one individual's nutritional status. In addition to being able to affect body condition, parasites can also influence the carotenoid coloration of birds' plumage, since carotenoids are obtained through diet, depending on the ability to forage. The main objective of this study was to measure the effects of malaria parasites on body condition and carotenoid coloration of pectoral plumage of birds in a Cerrado’s area in the Clube do Caça e Pesca Itororó’s Reserve, in the city of Uberlândia, Minas Gerais, Brazil. Individuals were captured using mist nets. The parasites were identified by microscopy and nested PCR. The plumage coloration was determined by reflectance using a portable spectrophotometer, generating the following variables: carotenoid chroma; chroma/saturation and hue. The analyzes were done using generalized linear mixed model, with parasitemia and/or presence/absence of parasites as explanatory variable and both body condition indices and coloration variables as response. As data were collected from several bird species, the identity of each was placed as the random factor in the models. The results showed that the parasitized individuals had lower concentrations of chroma of carotenoids and less saturated pectoral feathers when compared with uninfected individuals. This indicates, therefore, a trade-off between carotenoid deposition for plumage coloration and for immune response, since carotenoids are also used as immune system stimulators. Neither the presence of parasites nor the proportion of infected cells explained differences in body condition indexes. As female birds possibly discriminate differences in carotenoid saturation and prefer more saturated males, the results suggest the direct negative influence of parasites that cause malaria in the sexual selection of the bird populations in a Cerrado’s area.