Habitat modifications such as deforestation and the increase of agricultural activities, have led to uncommon faunal interactions. In Colombia, this condition have caused the secondary contact of subspecies of Ramphocelus flammigerus populations from Cauca valley and the Pacific coast; and some specimens with rumps of intermediate colors of the subspecies have been found and are thought as hybrids. The objective of this study was to assess the presence of morphological evidence that may suggest hybridization and may explain the origin of individuals with intermediate coloration. We predict that if subspecies hybridize, they will be more similar in morphology when coexisting than when separated. Alternatively, coexisting subspecies might diverge in sympatry, because of selection to reduce competition for resources (character displacement). For this, a survey in 15 localities was undertaken: 10 allopatric areas (five for each subspecies), and five sympatric areas. Mist nets were used to capture individuals and a total of seven morphological characters were measured. To identify the patterns of morphological variation, we compared morphology of subspecies, sympatric and allopatric populations and individuals of intermediate colors. Consequently, we performed discriminant analysis and test for differences between groups by using 95% confidence intervals for log-ratio tests. A total of 112 individuals were captured (46 intermediate-colored individuals, 20 R. f. flammigerus, and 46 R. f. icteronotus. Discriminant analyses showed that subspecies were well differentiated, and intermediate individuals overlapped with them. Log-ratio test, based on Mahalanobis distances, showed that intermediate individuals were morphologically more similar to both subspecies than subspecies themselves. In addition, log-ratio tests showed that subspecies sympatric populations were similar but allopatric ones were different, and that individuals of intermediate colors were more similar to sympatric than to allopatric populations of the two subspecies. Therefore, morphological evidence supports the predictions of a hybridization hypothesis among the subspecies of R. flammigerus. In conclusion, the analysis of morphological variation in R. flammigerus suggests that hybridization between subspecies is occurring and that a process of genetic introgression is probably in progress.
Keywords: hybridization, morphology, introgression, sympatric, allopatric, character displacement, ramphocelus