Figure 4.

Different adult vocal learners (A–G), non-learners (H), and a crocodile (I) shared the FoxP2 expression pattern in the striatum and dorsal thalamus (DT) but differed in expression levels in the striatal vocal nucleus (Area X/VAS/MMSt). Area X of chickadees (sampled in the fall), strawberry finches (sampled on long day photoperiod), and canaries (sampled in July) expressed more FoxP2 in Area X than in the surrounding striatum (A–C), reflected in higher expression ratios (bars A–C in J). Area X of song sparrows (sampled in spring) expressed slightly less FoxP2 than the surrounding striatum (D; bar D in J), as did Bengalese finch (E; bar E in J). The rufous-breasted hermit hummingbird (F) had slightly higher expression in the VAS, and the parrot (G) did not show a difference between vocal nucleus MMSt and the surrounding striatum. The adult ringdove (H), a bird that does not exhibit vocal learning and lacks telencephalic vocal nuclei, expressed high levels of FoxP2 mRNA in the striatum and DT, as did a crocodile (I). The arrow in C points to the high levels of FoxP2 expression in the substantia nigra pars compacta. M, Mesopallium; MO, oval nucleus of the mesopallium; N, nidopallium; St, striatum; VAS, vocal nucleus of the anterior striatum; MMSt, magnocellular nucleus of the medial striatum. Scale bars (in A for A–E;in H for H, I), 2 mm.