Estresse oxidativo de aves em clareiras naturais e sub-bosque na região Amazônica

Abstract

Background: (Oxidative stress of birds in natural gaps and understory sites in the Amazon region). Studies that provide information about the distribution of birds in different phases of forest mosaic are essential for understanding the maintenance of biodiversity, since natural gaps play a central role on the structure and dynamics of tropical forest. Objectives: (a) to determine and compare the abundance and richness of frugivorous birds between the natural gap and understory habitats; (b) verify and associate the abundance of frugivorous birds with the availability of fruits in both areas; (c) to investigate the echophysiological interactions between the oxidative stress and the distribution of specimens of Dixiphia pipra and Willisornis poecilinotus, to determine which factors account for the variance of biomarkers of oxidative stress in these species. Methods: This study was carried out from November 2010 to October 2011 in terra firme forest sites at the National Forest of Caxiuanã, Melgaço, Pará, Brazil. Two different understory forest habitats were selected for sampling on the basis of physiognomies: natural tree fall gap and undisturbed forest. Twelve (12) sites were selected (6 natural gaps and 6 undisturbed continuous forests). In each site, groups of 10 mist nets were set at ground level which remained open from 6:00am to 2:00pm for two consecutive days, totaling six days each month. This procedure lasted for 12 months and the sampling effort totaled 23,040 mist net hours. All specimens captured were identified, marked with metal rings and kept in cotton bags. We collected blood, feces and regurgitation samples to determine the biomarkers of oxidative stress and the composition of the diet. The relationship between thiobarbituric acid reactive substances and the total antioxidant capacity was used as an index of oxidative stress. The vegetation structure was determined based on transects along the mist nets; the plants bearing fruits were identified and the total antioxidant capacity was determined in each plant. Results: During the period of the study 347 specimens of 21 species were sampled. The assemblage of frugivorous birds in natural gap is distinct from that of undisturbed forest sites. The species responsible for dissimilarity were Dixiphia pipra, Pipra rubrocapilla and Turdus albicollis. The richness of birds was similar in both sites, but the availability of fruits and the total capture index were higher in natural gaps. The primary frugivores (those whose feces or regurgitation always showed fruit pulp or seeds) occurred mainly in natural gaps, where the most abundant species was Dixiphia pipra. In addition, Pipra rubrocapilla was the most abundant species in undisturbed sites. Thirty-six (36) species of plants bearing fruits were recorded, and the abundance of frugivorous birds was significantly correlated with the number of plants bearing fruits in natural gaps, where the most common species of plants were: Psychotria colorata and Psychotria iodotricha. On the other hand, Faramea anisocalyx and Virola surinamensis were the most common species in undisturbed sites. The variation of biomarkers of oxidative stress in specimens presenting lek behavior varied with gender and to the site of sampling. In natural gaps, the adult males of Dixiphia pipra showed higher levels of oxidative stress. The high metabolic rate resulting of flight effort to avoid predators, courtship behavior to the female and territory defense, can increase the production of pro-oxidant compounds. However, the ingestion of fruits with high content of antioxidant compounds by male can minimize the deleterious effects of oxidative stress. The variance of oxidative stress of species that do not have organization in leks was associated only with the site of sampling. The specimens sampling in natural gaps showed higher levels of oxidative stress. This can be due to the increase in metabolic rate to avoid predators as well as new flight strategies for foraging.