Hybridization in Andean warblers: how color, song, and genes interact in avian hybrid zones

Methods

Summary

The Spectacled Redstart (Myioborus melanocephalus) is a colorful warbler that is found along the cloud forests of the Andes from Bolivia to southern Colombia. It is precisely in northern Ecuador and southern Colombia where this species overlaps with another warbler, the Golden-fronted Redstart (M. ornatus), which extends northwards along the Western and Central cordilleras of Colombia. In the area of contact between the two bird species (Nariño and western Putumayo in Colombia, and Carchi and Sucumbíos in Ecuador) birds with intermediate appearance are found, suggesting hybridization between these warblers. Field work will be focused in this area, where I will establish a transect covering the extent of the contact zone along the eastern slope of the Andes. In addition, I will conduct field work away from the contact zone in to have a reference of “pure” populations, in Antioquia, Colombia (pure ornatus) and Loja, Ecuador (pure melanocephalus). I will include in the study existing museum specimens of these two warblers and from the contact zone to supplement the new specimens that I will collect. Specimens of these warblers will allow me be analyze what characteristics of plumage coloration vary with respect to parental species and how are they combined in hybrids, and will be the primary source of DNA to conduct the genetic analyses. To describe variation in song I will record songs and call in the field and also use recordings available from song archives. 

To describe variation in plumage, I will analyze the color parts of the body that differ between species and that may vary in different ways in the hybrid individuals : extent of rufous in the head, extent of black on the forehead, extent of white in the sides of the face (auricular), amount of black (vs. yellow) on the face, and coloration of the back and belly. I will estimate the surface area of each color patch using scaled photographs. To assess song variation, I will measure parameters such as frequency, total length and number of notes on spectrograms generated from recordings of song bouts. To describe genetic variation I will use a technique that allows to sample many regions across the genome, called genotyping-by-sequencing (GBS). This will allow me describe genetic variation taking into account many genes, instead of focusing on one region (e.g single mitochondrial gene) that might not show variation between the species given their recent divergence. Then I will compare the patterns of genetic variation to variation in the different signaling traits, which will allow me to make inference on their importance for reproductive isolation in these hybridizing warblers