FIGURE 1.

Species, sex, and plasma androgen level are the major determinants of the HVC gene expression patterns in songbirds. (A) HVC volume of birds used in this study. Forest weavers: males 0.528 mm³ (mean), females 0.357 mm³. Mann–Whitney Test, U = 7, P-value = 0.0931. Cordon-bleus: males 0.245 mm³, females 0.136 mm³. Mann–Whitney Test, U = 0, P-value = 0.00217. Breeding canaries: singing males 0.439 mm³, non-singing females 0.116 mm³. Mann–Whitney Test, U = 0, P-value = 0.00217. Non-breeding canaries: non-singing males 0.228 mm³, non-singing females 0.103 mm³, singing females 0.176 mm³. Mann–Whitney Test (non-singing males vs. non-singing females), U = 0, P-value = 0.00492. Mann–Whitney Test (non-singing males vs. singing females), U = 8, P-value = 0.127. Testosterone-implanted canaries: males 0.478 mm³, females 0.253 mm³. Mann–Whitney Test, U = 0, P-value = 0.0238. *P-value < 0.05; **P-value < 0.01. Each colour-coded dot indicates the measurement from one bird. The boxes indicate the 25th/50th/75th percentiles (bottom/middle/top bar), and the extent of the whiskers indicates the most extreme values that are within 1.5 times the IQR (interquartile range) of the hinge. T, testosterone; music note, presence of singing behaviour. (B) Hierarchical clustering showing that phylogenetic relatedness accounts for the most variation in the HVC transcriptomes of females and males of the forest weaver, cordon-bleu, and canary. Among the seven canary groups, the testosterone-treated animals were the least similar to the untreated canaries. (C) A PCA of the HVC transcriptomes of the seven canary groups distinguished male birds (PC2 < 0) from female birds (PC2 > 0). Each point is colour-coded by group (see panel B) and represents an HVC sample.