A juvenile locomotor program promotes vocal learning in zebra finches

Abstract

The evolution and development of complex, learned motor skills are thought to be closely associated with other locomotor movement and cognitive functions. However, it remains largely unknown how different neuromuscular programs may interconnect during the protracted developmental process. Here we use a songbird to examine the behavioral and neural substrates between the development of locomotor movement and vocal-motor learning. Juvenile songbirds escalate their locomotor activity during the sensitive period for vocal learning, followed by a surge of vocal practice. Individual variability of locomotor production is positively correlated with precision of tutor imitation and duration of multi-syllable sequences. Manipulation of juvenile locomotion significantly impacts the precision of vocal imitation and neural plasticity. The locomotor program developed during the sensitive period of vocal learning may enrich the neural substrates that promote the subsequent development of vocal learning.

Fig. 1. Developmental trajectories of juvenile locomotor movement are associated with vocal practice.

a The amount of locomotor activity of juvenile male finches (i.e., mean and standard error of total moving distance, shown in light green bars, n = 13 birds) across part of the sensitive period of vocal learning from 33-65 dph. Each juvenile was housed in a semi-social environment. Each blue dot depicts the mean moving distance of each individual bird at a given age. The adult males (dark blue bar, 183–390 dph, n = 10 birds) had less locomotor movement than that of juveniles. The peak of juvenile locomotor activity (around day 38) came before the peak of juvenile song production (after day 50; orange line depicts the mean of the total number of syllables produced from 33-65 dph). b Developmental schedule of vocal learning in zebra finches. c The within-day motor activity of juvenile locomotor movement (blue line represents the mean of the total distance moved) and number of song syllables produced (orange line). Each data point is the mean of total moving distance (cm) or total syllable number throughout the day, across the sensitive period from 33 to 65 dph for 6 juvenile males. d Examples show two juveniles’ developmental trajectories of locomotor activity from 33 to 65 dph. Top panel of each bird: each blue line represents the total moving distance (cm) per 6 min; bottom panel: the orange graph represents mean number of song syllables per hour. The light green block depicts the peak of the locomotor activity or song production in each bird.

Fig. 2. Developmental trajectories of individual juveniles’ locomotor movement and song production.

a Each graph shows the trajectory of locomotor activity (light blue bars) and syllable production (orange line) of each juvenile male (n = 9 birds that had complete song recordings) across part of the sensitive period of vocal learning from 33 to 65 dph. The three birds on the top (Birds 1-3) had more locomotor movement, more song syllable production, and better tutor song imitation (87, 89, and 86% of similarity match to the tutor song respectively), whereas the three birds on the bottom (Birds 7–9) had less movement, less song production and poor tutor imitation (45, 47, 43%, respectively). These juveniles were housed in a semi-social setting in Fig. 1a. b The amount of locomotor activity (average of cumulative moving distance from 33-65 dph) is correlated with the production of syllable numbers. Each number denotes a bird ID from (a). c Developmental trajectories of juvenile locomotor movement in a social setting. The amount of locomotor activity of juvenile male finches (i.e., mean and standard error of cumulative moving distance, shown in light blue bars, n = 6 birds) across part of the sensitive period of vocal learning from 33 to 65 dph. Each juvenile was housed together with its father tutor from 0 to 65 dph. This social setting, however, did not allow us to quantify the song development.

Fig. 3. Individual variation in juvenile locomotor activity was correlated with precision of tutor song imitation.

a The average amount of locomotor activity (i.e., mean of total moving distance from 35 to 65 dph, n = 13 birds) of individual juveniles was positively correlated with similarity match of tutor song. b The syllable sequential match (%) of the tutor song was positively correlated with the amount of locomotor activity. c The duration of multisyllable motif was positively correlated with the amount of locomotor activity, and similarly, d however, individual’s locomotor movement was not associated with the ratio between the tutee’s motif duration and tutor’s motif duration, that is, the ratioi between the tutee’s motif duration and tutor’s motif duration. e Examples show the correlation between juvenile locomotor activity and song learning. The juveniles (Bk899 and lB31) that had more locomotor activity at the juvenile stage also produced a better match of tutor song (60% and 65% respectively) and sequential match (81% and 84%, respectively) than their biologically-related siblings (W21 and lB33; 44% and 45% of tutor song similarity match and 58% and 53% sequential match). Both father tutors (Pi10 and O288) had long motif duration (1448 and 1103 milliseconds respectively). Sonograms depict the crystallized songs recorded from sibling males at around 100 dph, each semi-transparent colored bar represents a syllable.

Fig. 4. Manipulation of juvenile locomotor activity affected song learning and neural plasticity.

a Sonograms show two family examples of song learning by either promoting locomotion activity with large cage housing, or restricting locomotion with wing clipping or small cage housing, during the sensitive period of song learning between 30 and 65 dph. Left panel. A juvenile kept in a large cage (Br34) had a longer multi-syllable sequence and better tutor imitation (76% match), compared to its sibling that was housed in a small cage (Br35 with 47% similarity match): the highlighted syllable (shown in Tutor 228 and a juvenile Br34) was a complex syllable and was missing in Br35. Right panel, wing-clipped bird (Bk113) had a shorter motif duration and lower similarity match (45%) compared to its tutor’s song (LG563) or its intact-control sibling (Bk115; 86% similarity match to tutor song). Similar syllable type between the tutor and the tutees was highlighted with the same color, the wing-clipped bird (Bk113) produced fewer syllables and syllables were less similar to its tutor, compared to its sibling (Bk115). b–e Birds housed in a large cage (green bar, n = 8) had significantly more movement (b), better song imitation (c), longer song motif (d), and longer motif duration ratio relative to the tutor song (e) compared to their siblings (light gray bar, n = 8) that were housed in a small cage (**P < 0.01, *P < 0.05). Similarly, wing-clipped birds (orange bar, n = 8) had significantly less moving distance, less similarity match to tutor song, and shorter motif length than their intact-control siblings (b–e), n = 8 birds; from 5 adult tutors). Each colored dot in a graph bar depicts an individual bird, and the gray line connects two sibling birds from the same clutch. The dashed lines in (c) represent the average similarity score between adult tutors (n = 8) and unrelated juveniles (n = 15) from other families. f BrdU-labeled neurons in a song nucleus HVC. Red: BrdU-labeled cells, Green: Hu-labeled neurons. Scale bar= 50 µm on the top images and 10 µm on the bottom image. g Juveniles housed in a smaller cage (n = 8 birds) and wing-clipped birds (n = 8 birds) had fewer BrdU-labeled neurons in two forebrain song nuclei (HVC and Area X, light orange and light blue bars respectively; error bars depict the mean and standard error of the number of BrdU+ neurons) compared to the birds housed in a larger cage and intact-control birds. Each dot represents an individual bird.