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[Show abstract] [Hide abstract]
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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ABSTRACT: Rapid effects of social interactions on transient changes in hormonal levels are known in a wide variety of vertebrate taxa, ranging from fish to humans. Although these responses are mediated by the brain, neurochemical pathways that translate social signals into reproductive physiological changes are unclear. In this study, we analyzed how a female presence modifies synthesis and/or release of various neurochemicals, such as monoamines and neuropeptides, in the brain and downstream reproductive hormones in sexually active male Japanese quail. By viewing a female bird, sexually active males rapidly increased norepinephrine (NE) release in the paraventricular nucleus (PVN) of the hypothalamus, in which gonadotropin-inhibitory hormone (GnIH) neuronal cell bodies exist, increased GnIH precursor mRNA expression in the PVN, and decreased luteinizing hormone (LH) concentration in the plasma. GnIH is a hypothalamic neuropeptide that inhibits gonadotropin secretion from the pituitary. It was further shown that GnIH can rapidly suppress LH release after intravenous administration in this study. Centrally administered NE decreased plasma LH concentration in vivo. It was also shown that NE stimulated the release of GnIH from diencephalic tissue blocks in vitro. Fluorescence double-label immunohistochemistry indicated that GnIH neurons received noradrenergic innervations, and immunohistochemistry combined with in situ hybridization have further shown that GnIH neurons expressed α2A-adrenergic receptor mRNA. These results indicate that a female presence increases NE release in the PVN and stimulates GnIH release, resulting in the suppression of LH release in sexually active male quail.The Journal of Neuroscience : The Official Journal of the Society for Neuroscience 07/2014; 34(29):9803-11. DOI:10.1523/JNEUROSCI.3706-13.2014 · 6.75 Impact Factor