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: 3.74). 07/1986; 20(2):222-34. DOI: 10.1016/0018-506X(86)90020-6
Source: PubMed

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.

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Environmental cues and social interactions are known to influence reproductive physiology and behavior in vertebrates. In female birds, male courtship displays can result in the growth of ovarian follicles, the production of reproductive hormones, and stimulation of oviduct development, all of which have the potential to influence maternal investment. Male Japanese quail follow a typical sequence of copulatory behaviors during a mating interaction and often force copulations with unreceptive females. We hypothesized that female Japanese quail could adjust maternal investment in response to male copulatory behaviors during a single mating interaction. We investigated the relationships between 1) male copulatory behaviors and post-mating concentrations of steroids in the female, 2) female steroid concentrations and fertilization success of inseminations and 3) female steroid concentrations and the offspring sex ratio. We found that male condition and copulatory behaviors predicted female steroid concentrations and maternal investment in eggs laid after a mating trial. The body condition of one or both mates was a significant predictor of the changes in female corticosterone and testosterone concentrations after mating, whereas specific male copulatory behaviors significantly predicted changes in female progesterone concentrations. Male and female body condition, male neck grabs and post-mating concentrations of female corticosterone, progesterone, and testosterone were all significant predictors of egg fertilization rates. Female body condition, male copulation efficiency, and female testosterone concentrations were significant predictors of offspring sex ratios. Our results show that phenotypic and behavioral characteristics of male Japanese quail modulate female steroid concentrations and result in changes in maternal investment.
    Hormones and Behavior 03/2011; 59(4):556-64. · 3.74 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Year-class differences in reproductive function were investigated in a free-living population of adult male Dark-eyed Juncos, Junco hyemalis, breeding in interior Alaska. Second-year males (SY, entering their first breeding season) were compared with after-second-year males (ASY, entering at least their second breeding season). We measured body mass, size of the cloacal protuberance (CP), testis mass, onset of prebasic molt, and concentrations of plasma luteinizing hormone (LH), testosterone (T), corticosterone (CORT), and prolactin (PRL) throughout the reproductive season (April to mid-July). There were no differences in SY and ASY body weights but SY males had smaller CPs and testis masses than ASY males during gonadal recrudescence and at the end of the breeding season. Plasma LH was elevated from April until mid-June and then decreased in the same way in both year classes. In contrast, plasma T was high from April until mid-May and was lower in SY than in ASY juncos shortly after they arrived on their breeding grounds at the end of April, but not at other times. In July, SY males started to molt earlier, suggesting that they became photorefractory earlier than ASY males. Plasma PRL increased progressively in both year classes between April and early June and decreased in early July. At this time, plasma PRL decreased earlier in SY than in ASY males. Plasma CORT changed seasonally, but did not differ between SY and ASY juncos. Thus, year-class differences in CP sizes and testis mass apparently did not result from SY males secreting less LH or more PRL or CORT than ASY males. It is suggested that differences in reproductive condition in SY and ASY juncos are mediated by interactions with conspecific birds and do not result from an intrinsic effect of age.
    General and Comparative Endocrinology 07/2000; · 2.82 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Artificial light at night is a rapidly increasing phenomenon and it is presumed to have global implications. Light at night has been associated with health problems in humans as a consequence of altered biological rhythms. Effects on wild animals have been less investigated, but light at night has often been assumed to affect seasonal cycles of urban dwellers. Using light loggers attached to free-living European blackbirds (Turdus merula), we first measured light intensity at night which forest and city birds are subjected to in the wild. Then we used these measurements to test for the effect of light at night on timing of reproductive physiology. Captive city and forest blackbirds were exposed to either dark nights or very low light intensities at night (0.3 lux). Birds exposed to light at night developed their reproductive system up to one month earlier, and also moulted earlier, than birds kept under dark nights. Furthermore, city birds responded differently than forest individuals to the light at night treatment, suggesting that urbanization can alter the physiological phenotype of songbirds. Our results emphasize the impact of human-induced lighting on the ecology of millions of animals living in cities and call for an understanding of the fitness consequences of light pollution.
    Proceedings of the Royal Society B: Biological Sciences 01/2013; 280(1756):20123017. · 5.68 Impact Factor