The influence of social cues on the reproductive endocrinology of male brown-headed cowbirds: Field and laboratory studies
The Rockefeller University Field Research Center, Millbrook, New York 12545 U.S.A. Hormones and Behavior
(Impact Factor: 4.63).
07/1986; 20(2):222-34. DOI: 10.1016/0018-506X(86)90020-6
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.
Available from: Kristal E Cain
- "Previous work has shown that both male–male competition and the presence of females can have an effect on T levels in male songbirds (Goymann, 2009; Ketterson et al., 1992; Wingfield et al., 1987). For example, male brown–headed cowbirds (Molothrus ater) housed with females maintain peak T levels longer than males housed singly (Dufty and Wingfield, 1986). In starlings, 60 min of females exposure was sufficient to elevate male T levels (Pinxten et al., 2003). "
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ABSTRACT: Testosterone is an important mediator of behavior, morphology and physiology. A cascade of signals regulates the amount of testosterone (T) circulating in the plasma; in response to stimulus the hypothalamus releases gonadotropin-releasing hormone (GnRH), which triggers secretion of gonadotropins from the pituitary, stimulating the synthesis and release of T from the gonads. Previous work has shown that changes to the social environment can alter circulating T-levels, which may have important fitness consequences, but it is currently unclear whether these changes are due to alterations in the signal from the brain, or changes in the ability of the pituitary and gonads to respond to this signal. Further, the strength and direction of response to a changing environment may differ according to life-history strategy. Species with genetically determined alternative strategies offer a pathway for examining these differences. Here we use a finch with a genetically determined polymorphism, the Gouldian finch (Erythrura gouldiae), to determine whether T-levels change in response to social environment. We also use injections of GnRH to determine whether these changes are due to alterations in the ability of the pituitary and gonads to respond to this signal. We found that social environment (presence of females) had a rapid effect on male circulating T-levels, and that this difference was reflected in responsiveness to GnRH. We observed no overall morph differences in T-levels, but we did observe morph differences in the pattern of T secretion across environments, and morph differences in the repeatability of T-levels across time and environment.
Available from: Davide Michelangelo Dominoni
- "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 . "
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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.
Available from: H Bobby Fokidis
- "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). "
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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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