| 1. |
- Deviche, Pierre J., et al.
(författare)
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Acute stress rapidly decreases plasma testosterone in a free-ranging male songbird: Potential site of action and mechanism
- 2010
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Ingår i: GENERAL AND COMPARATIVE ENDOCRINOLOGY. - 0016-6480. ; 169:1, s. 82-90
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Tidskriftsartikel (refereegranskat)abstract
- We used a free-ranging, seasonally breeding adult male songbird, the rufous-winged sparrow, Aimophila carpalis, to investigate the effects of acute stress-induced by capture followed by restraint, on the hypothalamo-pituitary–testicular axis. Intra- and interindividual comparisons revealed that males decreased their plasma testosterone (T) by 37–52% in response to acute stress. The decrease occurred within 15 min of capture and persisted for at least another 15 min. Within 15 min, the decrease in plasma T was not associated with a reduction in plasma luteinizing hormone (LH). Thirty minutes after capture and restraint, the decrease in plasma T either was likewise not associated with decreased plasma LH (intraindividual comparison) or concurred with a reduction in plasma LH (interindividual comparison). These observations indicate that effects of stress may have been mediated at the pituitary gland and also directly at the testicular levels. To address this question, we measured the hormonal response to an injection of the glutamate receptor agonist N-methyl-d,l-aspartate (NMA) to stimulate to stimulate the release of gonadotropin-releasing hormone (GnRH) or of GnRH to stimulate the release of LH. Treatment with NMA did not change plasma LH, presumably because the birds were in breeding condition and already secreting GnRH at a maximum rate. Administration of GnRH increased plasma LH equally in birds that were or were not stressed before the treatment. An injection of purified ovine LH (oLH) increased plasma T equally in birds that were or were not acutely stressed before the hormone injection. Thus, the observed acute stress-induced decrease in plasma T was apparently not mediated by decreased responsiveness of the pituitary gland to GnRH or of the testes to LH. Decreased plasma T following stress may involve a direct impairment of the testicular endocrine function.
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| 2. |
- Both, C., et al.
(författare)
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Large-scale geographical variation confirms that climate change causes birds to lay earlier
- 2004
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Ingår i: Proceedings of the Royal Society of London Series B-Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 271:1549, s. 1657-1662
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Tidskriftsartikel (refereegranskat)abstract
- Advances in the phenology of organisms are often attributed to climate change, but alternatively, may reflect a publication bias towards advances and may be caused by environmental factors unrelated to climate change. Both factors are investigated using the breeding dates of 25 long-term studied populations of Ficedula flycatchers across Europe. Trends in spring temperature varied markedly between study sites, and across populations the advancement of laying date was stronger in areas where the spring temperatures increased more, giving support to the theory that climate change causally affects breeding date advancement.
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| 3. |
- Both, C., et al.
(författare)
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Pied Flycatchers Ficedula hypoleuca travelling from Africa to breed in Europe: differential effects of winter and migration conditions on breeding date
- 2006
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Ingår i: ARDEA. - 0373-2266 .- 2213-1175. ; 94:3, s. 511-525
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Tidskriftsartikel (refereegranskat)abstract
- In most bird species there is only a short time window available for optimal breeding due to variation in ecological conditions in a seasonal environment. Long-distance migrants must travel before they start breeding, and conditions at the wintering grounds and during migration may affect travelling speed and hence arrival and breeding dates. These effects are to a large extent determined by climate variables such as rainfall and temperature, and need to be identified to predict how well species can adapt to climate change. In this paper we analyse effects of vegetation growth on the wintering grounds and sites en route on the annual timing of breeding of 17 populations of Pied Flycatchers Ficedula hypoleuca studied between 1982–2000. Timing of breeding was largely correlated with local spring temperatures, supplemented by striking effects of African vegetation and NAO. Populations differed in the effects of vegetation growth on the wintering grounds, and on their northern African staging grounds, as well as ecological conditions in Europe as measured by the winter NAO. In general, early breeding populations (low altitude, western European populations) bred earlier in years with more vegetation in the Northern Sahel zone, as well as in Northern Africa. In contrast, late breeding populations (high altitude and northern and eastern populations) advanced their breeding dates when circumstances in Europe were more advanced (high NAO). Thus, timing of breeding in most Pied Flycatcher populations not only depends upon local circumstances, but also on conditions encountered during travelling, and these effects differ across populations dependent on the timing of travelling and breeding.
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| 4. |
- Lindsay, Willow, 1980, et al.
(författare)
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Corticosterone: a costly mediator of signal honesty in sand lizards
- 2016
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 6:20, s. 7451-7461
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Tidskriftsartikel (refereegranskat)abstract
- The mechanisms underlying honest signal expression remain elusive and may involve the integration of social and physiological costs. Corticosterone is a socially modulated metabolic hormone that mediates energy investment and behavior and may therefore function to deter dishonest signal expression. We examined the relationship between corticosterone and green badge coloration in male sand lizards (Lacerta agilis), hypothesizing that physiological and behavioral costs resulting from elevated baseline glucocorticoids function in maintenance of honest signal expression. We found that large-badged males had higher corticosterone titer, with this relationship apparent at the end of the season and absent early in the season. Large-badged males also suffered higher ectoparasite load (number of tick nymphs), despite being in better condition than small-badged males. Ectoparasite load was positively related to corticosterone titer early in the season at the time of badge formation. High-condition individuals had lower corticosterone and lower numbers of ectoparasites than low-condition individuals, suggestive of conditional variation in ability to withstand costs of corticosterone. We found an opposing negative relationship between corticosterone titer and endoparasite load. Corticosterone titer was also negatively associated with male mobility, a fitness-determining behavior in this species. Because badge size is involved in mediating agonistic social interactions in this species, our results suggest that badge-dependent variation in corticosterone is likely reflective of variation in social conditions experienced over the course of the season. Our results implicate corticosterone in maintenance of signal honesty, both early in the season through enforcement of physiological costs (ectoparasite load) and during the season through behavioral costs (male mobility). We propose that socially modulated variation in corticosterone critically functions in mediation of signal honesty without requiring a direct role for corticosterone in trait expression.
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| 5. |
- Lõhmus, Mare, 1972, et al.
(författare)
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Chronic administration of leptin in Asian Blue Quail
- 2006
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Ingår i: Journal of Experimental Zoology Part a-Comparative Experimental Biology. - : Wiley. - 1548-8969 .- 1552-499X. ; 305A:1, s. 13-22
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that leptin has the capacity to reduce food intake, cause body weight loss, and increase energy expenditure in several vertebrate species. In this study, we investigated the effects of chronically elevated leptin levels on behavior and physiology of Asian Blue Quail (Coturnix chinensis). Fifteen male quail were treated with chicken leptin dissolved in phosphate-buffered saline (PBS) via subcutaneously inserted osmotic pumps that released approximately 1 mu g/g body weight/day during a 14-day period. Another 15 males acted as controls and their pumps released PBS only. All males were housed together with two females. We observed a decrease in body weight and feeding behavior in leptin-treated birds, but not in control birds, after 2 days of treatment. Thereafter, all birds increased in weight. Males treated with leptin were more active and more likely to preen the day after the beginning of the treatment. Plasma cholesterol levels in leptin birds decreased during the first week of treatment and plasma triglycerides tended to remain lower compared to the controls during the whole 2-week period of treatment. Glucose levels appeared stable during the observation period. Leptin-treated males remained closer to accompanying females than did control males, and females together with leptin males took longer to lay their first egg compared to females together with control males. This is the first article showing the effect of leptin on cholesterol and triglyceride levels in birds. We also observed a change in the activity and male-female interaction pattern in tested quail.
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| 6. |
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| 9. |
- Perfito, N., et al.
(författare)
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Anticipating Spring: Wild Populations of Great Tits (Parus major) Differ in Expression of Key Genes for Photoperiodic Time Measurement
- 2012
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Ingår i: Plos One. - : Public Library of Science (PLoS). - 1932-6203. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- Measuring day length is critical for timing annual changes in physiology and behavior in many species. Recently, rapid changes in several photoperiodically-controlled genes following exposure to a single long day have been described. Components of this 'first day release' model have so far only been tested in highly domesticated species: quail, sheep, goats and rodents. Because artificial selection accompanying domestication acts on genes related to photoperiodicity, we must also study this phenomenon in wild organisms for it to be accepted as universal. In a songbird, the great tit (Parus major), we tested whether a) these genes are involved in photoperiodic time measurement (PTM) in a wild species, and b) whether predictable species and population differences in expression patterns exist. Using quantitative RT-PCR, we compared gene expression after a single long day in male great tits from Sweden (57 degrees 42'N) with that from a German (47 degrees 43'N) population. Hypothalamic gene expression key for PTM changed only in the northern population, and occurred earlier after dawn during the single long day than demonstrated in quail; however, gonadotropins (secretion and synthesis) were stimulated in both populations, albeit with different timing. Our data are the first to show acute changes in gene expression in response to photostimulation in any wild species not selected for study of photoperiodism. The pronounced differences in gene expression in response to a single long day between two populations raise exciting new questions about potential environmental selection on photoperiodic cue sensitivity.
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| 10. |
- Silverin, Bengt, 1944, et al.
(författare)
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Ambient temperature effects on photo induced gonadal cycles and hormonal secretion patterns in great tits from three different breeding latitudes
- 2008
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Ingår i: Hormones and Behavior. - : Elsevier BV. - 1095-6867 .- 0018-506X. ; 54:1, s. 60-8
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Tidskriftsartikel (refereegranskat)abstract
- The present study determines how populations of great tits (Parus major) breeding in southern, mid and northern European latitudes have adjusted their reproductive endocrinology to differences in the ambient temperature during the gonadal cycle. A study based on long-term breeding data, using the Colwell predictability model, showed that the start of the breeding season has a high predictability ( approximately 0.8-0.9) at all latitudes, and that the environmental information factor (I(e)) progressively decreased from mid Italy (I(e)>4) to northern Finland (I(e)<1). The results indicate that integration of supplementary information, such as ambient temperature, with photoperiodic initial predictive information (day length), becomes progressively more important in maintaining the predictability of the breeding season with decreasing latitude. This hypothesis was verified by exposing photosensitive Great Tits from northern Norway, southern Sweden and northern Italy to sub-maximal photo-stimulatory day lengths (13L:11D) under two different ambient temperature regimes (+4 degrees C and +20 degrees C). Changes in testicular size, plasma levels of LH and testosterone were measured. The main results were: (1) Initial testicular growth rate, as well as LH secretion, was affected by temperature in the Italian, but not in birds from the two Scandinavian populations. (2) Maximum testicular size, maximum LH and testosterone levels were maintained for a progressively shorter period of time with increasing latitude, regardless of whether the birds were kept on a low or a high ambient temperature. (3) In birds from all latitudes, the development of photorefractoriness, as indicated by testicular regression and a decrease in plasma levels of LH and testosterone, started much earlier (with the exception for LH Great Tits from northern Scandinavia) when kept on +20 degrees C than when kept on +4 degrees C. The prolonging effects of a low temperature was more pronounced in Mediterranean birds, than in birds from Scandinavia, and more pronounced in Great Tits from southern Scandinavia than in Great Tits from northern Scandinavia. Ecological implications of the results are discussed, as well as possible impact of global warming on the breeding success of European Great Tits from different breeding latitudes.
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