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. "

    Full-text · Dataset · Oct 2015
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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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    ABSTRACT: Seasonal variation in social behavior is often accompanied by seasonal variation in communication. In mammals, how seasonal environmental cues influence aggressive vocalizations remains underexplored. Photoperiod is the primary cue coordinating seasonal responses in most temperate animals, including Siberian hamsters (Phodopus sungorus), a species that undergoes reproductive inhibition and increased aggression in winter. During same-sex aggressive encounters, hamsters emit both broadband calls (BBCs) and ultrasonic vocalizations (USVs) that indicate aggression and the vocalizer's sex, respectively; however, it is not known whether these rodents adjust specific elements of their vocal repertoire to reflect their photoperiod-induced seasonal phenotypes. To address this, we recorded vocalizations emitted during dyadic interactions between male or female pairs of hamsters housed in long or short photoperiods and measured serum testosterone levels. USV emission rate remained stable across photoperiods, but proportional use of USV subtypes varied in novel ways: 'jump' USVs were sensitive to seasonal phenotype, but not the vocalizer's sex, whereas 'plain' USVs were sensitive only to the sex of the vocalizer. BBC emission rate varied with seasonal phenotype; short-day non-reproductive hamsters produced more BBCs and demonstrated increased aggression compared with reproductive hamsters. Testosterone, however, was not related to vocalization rates. Collectively, these findings demonstrate that changes in the vocal repertoire of Siberian hamsters reflect sex, aggression, and seasonal phenotype, suggesting that both BBCs and USVs are important signals used during same-sex social encounters.
    Full-text · Article · Sep 2015 · Physiology & Behavior
    • "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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    ABSTRACT: Naked mole-rats (Heterocephalus glaber) live in groups that are notable for their large size and caste structure, with breeding monopolized by a single female and small number of males. Recent studies have demonstrated substantial differences between the brains of breeders and subordinates induced by changes in social standing. CRF receptors-which bind the hormone corticotropin-releasing factor as well as related peptides-are important regulators of stress and anxiety, and are emerging as factors affecting social behavior. We conducted autoradiographic analyses of CRF1 and CRF2 receptor binding densities in female and male naked mole-rats varying in breeding status. Both globally and in specific brain regions, CRF1 receptor densities varied with breeding status. CRF1 receptor densities were higher in subordinates across brain regions, and particularly in the piriform cortex and cortical amygdala. Sex differences were present in CRF2 receptor binding densities, as is the case in multiple vole species. CRF2 receptor densities were higher in females, both globally and in the cortical amygdala and lateral amygdalar nucleus. These results provide novel insights into the neurobiology of social hierarchy in naked mole-rats, and add to a growing body of work that links changes in the CRF system with social behavior. This article is protected by copyright. All rights reserved. © 2015 Wiley Periodicals, Inc.
    No preview · Article · Jun 2015 · The Journal of Comparative Neurology
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