Brightfield images (left column) and inverted darkfield images of transverse sections showing <i>egr-1</i> expression within sampling windows (boxes) in response to conspecific whine-chucks (middle column) and heterospecific whines (right column) in the anterior preoptic nucleus (A), septum (B), striatum (C), and medial pallium (D).

<p>Scale bars represent 400 µm. Abbreviations: Acc, nucleus accumbens; dMP, dorsal part of the medial pallium; DP, dorsal pallium; dStr, dorsal striatum; LP, lateral pallium; MP, medial pallium; POa, anterior preoptic nucleus; Sd, dorsal septal nucleus; Sl, lateral septal nucleus, Sld, dorsolateral septal nucleus; Slv, ventrolateral septal nucleus; Sm, medial septal nucleus; Str, striatum; vMP, ventral part of the medial pallium; VP, ventral pallium; vStr, ventral striatum.</p

Effects of acoustic stimuli on <i>egr-1</i> expression when stimuli reflected interspecific (Experiment 1) and intraspecific (Experiment 2) variation in mating calls.

<p>Abbreviations: A, anterior thalamus; C, central thalamus; DMN, dorsal medullary nucleus; dMP, dosal part of the medial pallium; Ltor, laminar nucleus of the torus semicircularis; MCtor, magnocellular nucleus of the torus semicircularis; P, posterior thalamus; POa, anterior preoptic nucleus; Ptor, principal nucleus of the torus semicircularis; Slv, ventral part of the lateral septum; SON, superior olivary nucleus; VH, ventral hypothalamus; vStr, ventral striatum.</p

Diagram of the major ascending and descending connections in the frog auditory system.

<p>Abbreviations: A, anterior thalamus; AP, amphibian papilla; BP, basilar papilla; C, central thalamus; DMN, dorsal medullary nucleus; Ltor, laminar nucleus of the torus semicircularis; MCtor, magnocellular nucleus of the torus semicircularis; MP, medial pallium; P, posterior thalamus; POa, anterior preoptic nucleus; Ptor, principal nucleus of the torus semicircularis; S, septum; SON, superior olivary nucleus; Str, striatum; VH, ventral hypothalamus.</p

Waveforms and spectrograms of the calls that we used to represent conspecific (<i>Physalaemus pustulosus</i>) and heterospecific (<i>Physalaemus enesefae</i>) mating calls in order to identify brain regions that contribute to species recognition.

<p>Waveforms and spectrograms of the calls that we used to represent conspecific (<i>Physalaemus pustulosus</i>) and heterospecific (<i>Physalaemus enesefae</i>) mating calls in order to identify brain regions that contribute to species recognition.</p

Effects of interspecific variation in mating calls on <i>egr-1</i> mRNA expression in the auditory brainstem and its forebrain targets.

<p>Data are shown as mean (± SE) fold change in silver grains per cell above background relative to the no sound group. Sample sizes are indicated for each group and letters above bars indicate groups that are statistically different (p<0.05). Abbreviations: A, anterior thalamus; C, central thalamus; DMN, dorsal medullary nucleus; dMP, dosal part of the medial pallium; Ltor, laminar nucleus of the torus semicircularis; MCtor, magnocellular nucleus of the torus semicircularis; P, posterior thalamus; POa, anterior preoptic nucleus; Ptor, principal nucleus of the torus semicircularis; Slv, ventrolateral septal nucleus; SON, superior olivary nucleus; VH, ventral hypothalamus; vStr, ventral striatum.</p

Effects of intraspecific variation in mating calls on <i>egr-1</i> mRNA expression in the auditory brainstem and its forebrain targets.

<p>Data are shown as mean (± SE) fold change in silver grains per cell above background relative to the no sound group. Sample sizes are indicated for each group. The bars above the columns indicate statistical comparisons between females hearing conspecific calls (whine or whine +3 chucks) to those hearing no sound and between females hearing the preferred, whine +3 chucks to those hearing whines; p values are indicated as follows: asterisks indicate p<0.05, actual p values are given for those tests where 0.050.2. Abbreviations: A, anterior thalamus; C, central thalamus; dMP, dosal part of the medial pallium; Ltor, laminar nucleus of the torus semicircularis; MCtor, magnocellular nucleus of the torus semicircularis; P, posterior thalamus; POa, anterior preoptic nucleus; Ptor, principal nucleus of the torus semicircularis; Slv, ventrolateral septal nucleus; SON, superior olivary nucleus; vStr, ventral striatum.</p

Brightfield images (left column) and inverted darkfield images of transverse sections showing <i>egr-1</i> expression within sampling windows (boxes) in response to conspecific whine-chucks (middle column) and heterospecific whines (right column) in the auditory brainstem (A–B) and thalamus (C–E).

<p>Scale bars represent 400 µm. Abbreviations: A, anterior thalamus; C, central thalamus; DMN, dorsal medullary nucleus; Fr, reticular formation; La, lateral thalamus; LH, lateral hypothalamus; Ltor, laminar nucleus of the torus semicircularis; OT, optic tectum; P, posterior thalamus; Ptor, principal nucleus of the torus semicircularis; SC, suprachiasmatic nucleus; SON, superior olivary nucleus; Teg, tegmentum; Tel, telencephalon; VH, ventral hypothalamus; VL, ventrolateral thalamus; VM, ventromedial thalamus.</p

Waveforms and spectrograms of the túngara frog (<i>Physalaemus pustulosus</i>) calls that we used to represent the whine and whine-chuck in order to examine responses of brain regions to mating calls that vary in their attractiveness.

<p>Waveforms and spectrograms of the túngara frog (<i>Physalaemus pustulosus</i>) calls that we used to represent the whine and whine-chuck in order to examine responses of brain regions to mating calls that vary in their attractiveness.</p

Identification of forebrain structures with specialized <i>parvalbumin</i> (<i>PV</i>) mRNA expression.

(A-F) Representative radioactive in situ hybridization microscope images of PV mRNA in species representing 8 different avian orders (see S1 Fig for penguin and emu). PV-rich forebrain nuclei were present in only (E) vocal learning hummingbirds (positive control) and (F) downy woodpeckers. (Ei-iii) High magnification of 3 telencephalic “song control” nuclei in hummingbirds. (Fi) High magnification of the woodpecker drumming nucleus of the anterior nidopallium (dAN); and (Fii) drumming nucleus of arcopallium (dA). Each scale bar is equal to 2 mm. Neuroanatomical markers shown in “A” are as follows: Hyper, hyperpallium; Meso, mesopallium; Nido, nidopallium; GP, globus pallidus; T, Thalamus; Ot, optic tectum; St, striatum; Arco, arcopallium; Ento, entopallium. White dashed lines in high-magnification images (Ei-iii and Fi-ii) indicate boundaries for different telencephalic regions (e.g., boundary between nidopallium and mesopallium), whereas blue dashed lines indicate specialized PV regions identified in Anna’s hummingbirds and downy woodpeckers. Image credits: flamingo from Wilfredo Rodríguez; turaco from Edelmauswaldgeist; duck from Orso della campagna e Papera dello stagno; hawk from Cheva; hummingbird from Stickpen, and downy woodpecker from Greg Schechter. All image licenses: CC Public Domain via WikiMedia.</p

Assessing striatal specializations and markers for the woodpecker arcopallium.

Two markers, (A) ETV1 and (B) Lhx9 (radioactive in situ hybridization), were used to delineate the boundary of the arcopallium and nidopallium. (C-F) Representative in situ hybridization images (inverted black and white colormetric) of (C and D) FoxP1 and (E and F) RGS12 in zebra finch and downy woodpecker. Both genes are significantly enriched in the zebra finch Area X (striatal nucleus); however, neither demarcates a specialized region within the woodpecker striatum. FoxP1 allows for the clear delineation of all nidopallial-striatal boundaries. Both reveal similar patterns to zebra finches (see [23]). Data from Lhx9 was collected through radioactive in situ hybridization (see Materials and methods for details). Hyp: hyperpallium; arco: arcopallium; nido: nidopallium; Meso: mesopallium. Scale bar, 500 μm. (TIF)</p