The influence of social cues on the reproductive endocrinology of male brown-headed cowbirds: Field and laboratory studies
ABSTRACT Captive male brown-headed cowbirds exposed to long days exhibit gonadal growth and have elevated plasma testosterone (T) levels. This photoperiodic response is enhanced if males are housed with female cowbirds: Photostimulated males with females increase plasma testosterone levels sooner than do individually housed photostimulated males. Peak plasma T levels are similar in both groups, although peak levels are maintained longer in males housed with females. The gonadal cycle is similarly affected; males in the presence of females have earlier gonadal recrudescence and maintain mature gonads longer than do photostimulated males without females. Plasma corticosterone levels increase in the unpaired males, suggesting that removal of social cues is stressful for these birds. Free-living paired males have significantly higher plasma testosterone levels than do unpaired/unknown males early in the season, when social relationships are being established; the levels are similar thereafter. There is no difference between the two groups in testicular maturation rates; nor do they differ in plasma corticosterone levels at any time of the season. These results suggest that social stimuli are important in modulating the secretion of testosterone in males early in the season when pairing occurs, and possibly late in the season as well, probably to prevent termination of breeding prior to that of females.
- SourceAvailable from: Davide Michelangelo Dominoni
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- "c o m / l o c a t e / p h b brain was enlarged when male white-crowned sparrows (Zonotrichia leucophrys gambelii) were housed with a fertile female compared to when they were housed alone . At the physiological levels, receptive male sparrows and cowbirds showed an increase in plasma concentrations of luteinizing hormone (LH) and testosterone when housed with a conspecific female  , and social stimuli emitted by females prevented testicular regression of male starlings (Sturnus vulgaris) . At the behavioral level, playback of male song was shown to influence the behavior of both male and female zebra finches (Taeniopygia guttata); males supplemented with playback song sang more frequently than non-supplemented males, and females who heard these extrasongs laid eggs earlier and increased clutch size compared to control females . "
ABSTRACT: Despite urban ecology being an established field of research, there is still surprisingly little information about the relative contribution of specific environmental factors driving the observed changes in the behaviour and physiology of city dwellers. One of the most reported effects of urbanization is the advanced phenology observed in birds. Many factors have been suggested to underline such effect, including warmer microclimate, anthropogenic food supply and light pollution. Since social stimuli are known to affect reproductive timing and breeding density is usually higher in urban populations compared to rural ones, we experimentally tested whether social interactions could advance the onset of reproduction in European blackbirds (Turdus merula). We housed male blackbirds of rural and urban origin with or without a conspecific female, and recorded their seasonal variation in gonadal size and production of luteinizing hormone (LH). Paired and unpaired males of both urban and rural origins did not significantly differ in their timing of gonadal growth. Moreover, rural and urban birds did not differ in their response to the social stimuli, rather they became reproductively active at the same time, a result that confirms previous studies that attributed the difference in reproductive timing observed in the field to phenotypic plasticity. We conclude that social stimuli do not contribute substantially to the observed early onset of reproductive physiology in urban bird species, rather other factors such as light pollution are likely to be stronger drivers of these physiological changes. Copyright © 2015. Published by Elsevier Inc.Physiology & Behavior 01/2015; 142. DOI:10.1016/j.physbeh.2015.01.026 · 3.03 Impact Factor
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- "Circulating gonadal hormones are known to affect the number of TH-positive cells in these same brain regions (Cavanaugh and Lonstein, 2010a, b; Northcutt and Lonstein, 2009; Northcutt et al., 2007; Wang et al., 1994). As in prairie voles, exposure to an opposite-sex conspecific results in gonadal hormone release in both male and female songbirds (Dufty and Wingfield, 1986; Gwinner et al., 2002; Kroodsma, 1976; Pinxten et al., 2003; Silverin and Westin, 1995). Additionally, increased expression of Fos proteins within TH-positive VTA and VMH neurons is observed following sexual behavior in rodents and birds (Balfour et al., 2004; Bharati and Goodson, 2006; Charlier et al., 2005; Heimovics and Riters, 2006; Kollack-Walker and Newman, 1995) and following exposure to a conspecific of either sex in male zebra finches (Bharati and Goodson, 2006). "
ABSTRACT: The catecholamines dopamine and norepinephrine are implicated in affiliative behaviors, yet few studies have addressed the extent to which affiliative behaviors within distinct social settings rely upon similar or distinct catecholaminergic mechanisms. To explore the role of catecholamines in affiliative behavior within distinct long-term social contexts, we examined the density of the catecholamine synthetic enzyme tyrosine hydroxylase (TH) in brain regions within both the mesolimbic dopaminergic system and "social behavior network" in male and female zebra finches (Taeniopygia guttata) paired for 21 days with either a same- or opposite-sex conspecific. On days 16-21 after pairing, members of both same- and mixed-sex pairs produced similar rates of affiliative behaviors. Measures of affiliation related to TH labeling in the ventral tegmental area (VTA), nucleus accumbens (Ac), medial preoptic nucleus (POM), and ventromedial nucleus of the hypothalamus (VMH). Relationships between TH labeling density and specific measures of affiliative behavior differed in rostral compared to caudal subregions of Ac and VTA, suggesting distinct roles for these subregions in the regulation of affiliative behavior. Finally, TH labeling density in the VMH and rostral VTA were positively related to the amount of courtship received from the partner and TH labeling in Ac was denser in opposite-sex pairs compared to same-sex pairs, indicative of socially induced brain plasticity. Overall, results highlight a complex region- and behavior-specific role for catecholamines in vertebrate affiliation.Journal of chemical neuroanatomy 05/2011; 42(1):45-55. DOI:10.1016/j.jchemneu.2011.05.005 · 2.52 Impact Factor
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- "Testicular function, particularly in monogamous species, is influenced by the presence of a mate. Captive male European starlings, Japanese quail, and brown-headed cowbirds that are kept without or with only limited exposure to a female exhibit a decreased capacity to develop their testes, and/or regress them sooner than males held with a female (Dawson & Goldsmith, 1984; Delville, Sulon, Hendrick, & Balthazart, 1984; Dufty & Wingfield, 1986b; Gwinner, Van't Hof, & Zeman, 2002). The importance of the pair bond is also demonstrated in crossbills, which can develop their testes and breed in winter provided that they receive proper food and are exposed to mates (Hahn et al., 2005). "
ABSTRACT: SUMMARY In many birds, testes undergo dramatic annual changes in size and, as such, are among the most anatomically and physiologically plastic organs found in adult vertebrates. Adult testicular function is modulated by a myriad of external factors and orchestrated by numerous hormones that together enable birds to adapt to and breed in diverse habitats worldwide. These factors have generated a wide range of avian reproductive strategies, which has further shaped testicular structure and function. This chapter describes the mechanisms that control avian exocrine and endocrine testicular functions. It analyzes how these functions are regulated by ecological and behavioral factors and presents an overview of how environmental information is integrated and transduced into appropriate gonadal responses. It also discusses testicular dysfunction and the potential effects of anthropogenic disturbances on testis function. The chapter emphasizes areas where knowledge is lacking or incomplete, with the hope of fostering additional research on this exciting and fruitful area of avian biology.01/2011: pages 27-70; Academic Press., ISBN: 9780123749291