Figure 2 : (a) Phylogenetic relationships of the avian taxa from which we obtained preen oil samples. The phylogenetic tree was made using Vertlife.org. (b) Agarose gel showing bands produced by PCR amplification of the V3-V4 regions of the 16S rRNA gene, using microbial DNA extracted from preen oil samples following our new protocol. The lanes of the 2% agarose gel pictured in (b) contain the PCR product from the uropygial gland microbiome of the avian species pictured directly above in the phylogeny (a). The negative control as well as a 50bp ladder are also included in the agarose gel. For samples lacking bands in this gel, see supplementary figures. Preen oil from the song sparrow was the only sample for which a band from PCR amplification of the V3-V4 regions of the 16S rRNA gene did not appear on any gel.