Morfometria e dieta de Trichothraupis melanops (Aves: Thraupidae): uma comparação entre sexos e áreas insular e continental de Mata Atlântica

Abstract

The morphology of an organism is a direct result of its evolution from its ecological adaptations to the habitat in which it lives and relates to its feeding and breeding behaviors. Body measurements differences between female and male have been associated with sexual selection or as a way to decrease intraspecific competition. Island population individuals compared to those from continental areas tend to be larger because of niche expansion due to less interspecific competition in islands. Analysis of morphometric data associated with diet composition may be a way to better understand the evolutionary responses of a species to these ecological factors. The present study aimed to investigate and compare the morphometric and dietary differences between sexes and insular (Ilha Grande) and continental (Cantagalo) areas of the Atlantic Forest, municipality of Angra dos Reis, RJ, for Trichothraupis melanops (Vieillot, 1818). Although this forest species has apparent sexual dimorphism, the present study used the CHD gene technique in order to separate young and subadults that have similar plumage to adult females. The birds were captured spontaneously from February 2014 to June 2016 with mist nets and had their body mass and 11 morphometric variables measured. We collected stool samples found inside the containment bags as well as blood samples from each captured individual (68 in Ilha Grande and 14 in Cantagalo). Sex misidentification based only on the plumage was 44%. Individuals from Ilha Grande had larger measures of total length, wing length, tail length, nostril height and distance from the tip of the beak to the head (HB), confirming the "island rule". Male wings are longer than females confirming the pattern found for other Passeriformes. However, as diet between sexes did not differ, this difference did not seem to be attributed to a diminished intraspecific competition. The most frequent food resources for both areas were Melastomataceae fruits and Hymenoptera and Coleoptera for arthropods. There was a greater diversity of food items in the insular area compared to the continental area, but the assymetric sampling does not allow us to indicate niche expansion in the insular area. More studies relating morphometry and diet between sexes comparing areas, as done by the present study between insular and continental areas, are necessary in order to better understand the causes for intraspecific morphological adaptations.