To flock or fight: Neurochemical signatures of divergent life histories in sparrows

Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 06/2012; 109 Suppl 1(Supplement_1):10685-92. DOI: 10.1073/pnas.1203394109
Source: PubMed


Many bird species exhibit dramatic seasonal switches between territoriality and flocking, but whereas neuroendocrine mechanisms of territorial aggression have been extensively studied, those of seasonal flocking are unknown. We collected brains in spring and winter from male field sparrows (Spizella pusilla), which seasonally flock, and male song sparrows (Melospiza melodia), which are territorial year-round in much of their range. Spring collections were preceded by field-based assessments of aggression. Tissue series were immunofluorescently multilabeled for vasotocin, mesotocin (MT), corticotropin-releasing hormone (CRH), vasoactive intestinal polypeptide, tyrosine hydroxylase, and aromatase, and labeling densities were measured in many socially relevant brain areas. Extensive seasonal differences are shared by both species. Many measures correlate significantly with both individual and species differences in aggression, likely reflecting evolved mechanisms that differentiate the less aggressive field sparrow from the more aggressive song sparrow. Winter-specific species differences include a substantial increase of MT and CRH immunoreactivity in the dorsal lateral septum (LS) and medial amygdala of field sparrows but not song sparrows. These species differences likely relate to flocking rather than the suppression of winter aggression in field sparrows, because similar winter differences were found for two other emberizids that are not territorial in winter--dark-eyed juncos (Junco hyemalis), which seasonally flock, and eastern towhees (Pipilo erythropthalmus), which do not flock. MT signaling in the dorsal LS is also associated with year-round species differences in grouping in estrildid finches, suggesting that common mechanisms are targeted during the evolution of different life histories.

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    • "Many temperate zone species demonstrate marked seasonal variation in social behavior, including gregariousness [1], aggression [2] [3], and reproductive behaviors [4]. Coupled with variation in social behavior , animals modify the use of their communicative signals on a seasonal basis. "

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    • "Many temperate zone species demonstrate marked seasonal variation in social behavior, including gregariousness [1], aggression [2] [3], and reproductive behaviors [4]. Coupled with variation in social behavior , animals modify the use of their communicative signals on a seasonal basis. "
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    • "During the time of year in which flocking occurs, field sparrows have greater CRF immunoreactivity in the lateral septum (Goodson et al., 2012), a region in which CRF 1 receptor binding has been associated with increased social huddling in meadow voles (Beery et al., 2014). Naked mole-rats have low to undetectable CRF 1 receptor binding in the lateral septum, but showed status differences in other brain regions. "
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