Variação geográfica, zonas de intergradação e especiação no complexo Icterus Cayanensis-Chrysocephalus (Aves : Icteridae)

Abstract

The Icterus cayanensis-chrysocephalus species complex shows an intricate pattern of geographic variation in body measurements and plumage. Traditionally, six taxa have been recognized in this group: Icterus chrysocephalus, I. cayanensis cayanensis, I. cayanensis tibialis, I. cayanensis valenciobuenoi, I. cayanensis periporphyrus and I. cayanensis pynhopterus, which replace each other geographically in South America. In this work, the geographic pattern of plumage and size variation was described for this species complex, and inferences were made about the evolutionary processes behind those pattern. Under the phylogenetic species concept (PSC), four species are diagnosed; Icterus cayanensis (Southern Amazon), I. chrysocephalus (Northern Amazon), I. tibialis (Caatinga) and I. pyrrhopterus (Chaco). The taxa lcterus cayenansis vaienciobuenoi lhering (1902) and Icterus cayanensis periporphyrus (Bonaparte 1950) were synonymizied. A hybrid zone more extensive than hitherto reported in the literature was detected between two Amazonian taxa: I. chrysocephalus and I. cayanensis. In Central Brazil, it was recognized one of the widest zones of intergradations known for birds to date, approximately 2.300 km wide, between I. tibialis and I. pyrrhopterus. R is postulated here that those hybrid zones were formed by secondary contact, after a period of differentiation in geographic isolation.