Dissociable effects of social context on song and doublecortin immunoreactivity in male canaries

Abstract

Variation in environmental factors such as day length and social context greatly affects reproductive behavior and the brain areas that regulate these behaviors. One such behavior is song in songbirds, which males use to attract a mate during the breeding season. In these species the absence of a potential mate leads to an increase in the number of songs produced, while the presence of a mate greatly diminishes singing. Interestingly, although long days promote song behavior, producing song itself can promote the incorporation of new neurons in brain regions controlling song output. Social context can also affect such neuroplasticity in these song control nuclei. The goal of the present study was to investigate in canaries (Serinus canaria), a songbird species, how photoperiod and social context affect song and the incorporation of new neurons, as measured by the microtubule-associated protein doublecortin (DCX) in HVC, a key vocal production brain region of the song control system. We show that long days increased HVC size and singing activity. In addition, male canaries paired with a female for 2 weeks showed enhanced DCX-immunoreactivity in HVC relative to birds housed alone. Strikingly, however, paired males sang fewer songs that exhibited a reduction in acoustic features such as song complexity and energy, compared with birds housed alone, which sang prolifically. These results show that social presence plays a significant role in the regulation of neural and behavioral plasticity in songbirds and can exert these effects in opposition to what might be expected based on activity-induced neurogenesis.

Keywords: canary; neurogenesis; plasticity; songbird.

Figure 1

A) Schematic of HVC and its main synaptic targets in RA and Area X. B) Effects of treatment on breeding condition as measured via the volume of the testis. Bar graphs are means ± SEM. Bars with a different letter are significantly different for p≤0.05, bars with a same letter are not different. C). Representative songs from each treatment group.

Figure 2

Effects of treatment on song output (A. Song rate (number per hour); B. Mean song duration) and its acoustic features (C. Energy; D. Entropy variance, see text for additional explanations) in male canaries. Bar graphs are means ± SEM. Bars with a different letter are significantly different for p≤0.05, bars with a same letter are not different.

Figure 3

The effects of treatment on DCX immunoreactivity in HVC and on HVC area. A) Representative photomicrograph depicting DCX round (left panel) and fusiform (right panel) cells. Magnification bar=50 µm B) Effects of treatment on the number DCX round cells per mm² in HVC. C) Effects of treatment on DCX fusiform cells per mm² in HVC. D) Effects of treatment on HVC area at its largest extension. Bar graphs are means ± SEM. Bars with a different letter are significantly different for p≤0.05, bars with a same letter are not different.