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.
"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 . "
"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). "
[Show abstract][Hide abstract] 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 · 1.50 Impact Factor
"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). "
[Show abstract][Hide abstract] 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.
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