Two Neural Measures Differ between Urban and Rural Song Sparrows after Conspecific Song Playback

Abstract

Urbanization is a critical form of environmental change that can affect the physiology and behavior of wild animals and, notably, birds. One behavioral difference between birds living in urban and rural habitats is that urban males show elevated boldness or territorial aggression in response to simulated social challenge. This pattern has been described in several populations of song sparrow, Melospiza melodia. Such behavioral differences must be underpinned by differences in the brain, yet little work has explored how urbanization and neural function may be interrelated. We explored the relationship between urbanization and neural activation within a network of brain regions, collectively called the social behavior network, which contributes to the regulation of territorial aggression. Specifically, we captured free-living, territorial male song sparrows by playing them conspecific songs for 6-11 min, and then collected their brains. We estimated recent neural activation, as indicated by the immediate early gene FOS, and measured levels of a neuropeptide, arginine vasotocin (AVT), which is involved in the regulation of social behavior. Based on previous studies we expected urban males, which are generally more territorially aggressive, to have lower FOS expression in a node of the social behavior network implicated in regulating territoriality, the lateral septum (LS). Additionally, we expected urban males to have lower AVT expression in a brain region involved in the regulation of sociality, the medial bed nucleus of the stria terminalis (BSTm). We found that, compared to rural males, urban male song sparrows did have lower FOS expression in the LS. This pattern suggests that lower neural activation in the LS could contribute to behavioral adjustments to urbanization in male song sparrows. Additionally, counter to our predictions, urban male song sparrows had higher AVT-like immunoreactivity in the BSTm. Future work building upon these findings is needed to determine the causal role of such neural differences across rural and urban habitats. Understanding the mechanisms impacted by urbanization will inform our understanding of the reversibility and consequences of this form of habitat change.

Effect of estradiol and predator cues on behavior and brain responses of captive female house sparrows (Passer domesticus)

“…Alternatively, we may have seen differences in IEG activation in response to predator and conspecific playbacks if had we examined expression of a different IEG, for example, c-Fos. Several studies have found differences in the expression of different IEGs in response to the same stimulus (Sewall and Davies, 2017;Kimball et al, 2022). We chose ZENK because it is commonly used to assess neuronal activity in songbirds in response to acoustic stimuli (Maney et al, 2003;Rivera et al, 2019); however, future studies should consider using multiple IEGs to examine the brain's response to positive, neutral, or aversive auditory cues.…”

Early life conditions that impact song learning in male zebra finches also impact neural and behavioral responses to song in females

“…We carried out immunohistochemistry for ZENK in every third section from both hemispheres following established protocols for application in bird tissue (Sockman et al, ; Sewall and Davies, ). Briefly, we blocked the tissue in 1% hydrogen peroxide followed by 2% normal goat serum and an Aviden Biotin blocking kit (Vector Labs, SP‐2001, Burlingame, CA) before incubating in Egr‐1 primary antibody (raised in rabbit, Santa Cruz Biotechnology, SC‐189, Dallas, TX) at a ratio of 1–8,000 for 48 h at 4°C.…”

“…We located the social behavior network regions following Maney et al (2008) and references therein (see also Sewall and Davies, 2017). Specifically, to identify BSTm, we followed Aste et al (1998) and Maney et al (2008) and placed a 0.2-mm 2 counting circle dorsal to the anterior commissure in two tissue sections.…”