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1.  Migration and stress during reproduction govern telomere dynamics in a seabird 
Biology Letters  2014;10(1):20130889.
Changes in telomere length are believed to reflect changes in physiological state and life expectancy in animals. However, much remains unknown about the determinants of telomere dynamics in wild populations, and specifically the influence of conditions during highly mobile life-history stages, for example migration. We tested whether telomere dynamics were associated with migratory behaviour and/or with stress during reproduction in free-living seabirds. We induced short-term stress during reproduction in chick-rearing, black-legged kittiwakes (Rissa tridactyla), tracked winter migration with geolocators and measured telomere length before and after winter migration. We found that time spent at wintering grounds correlated with reduced telomere loss, while stress during reproduction accelerated telomere shortening. Our results suggest that different life-history stages interact to influence telomere length, and that migratory patterns may be important determinants of variation in an individual's telomere dynamics.
PMCID: PMC3917333  PMID: 24429681
overwintering; migratory behaviour; breeding; seasonal effects; carry-over; telomeres
2.  To breed or not to breed: endocrine response to mercury contamination by an Arctic seabird 
Biology Letters  2013;9(4):20130317.
Mercury, a ubiquitous toxic element, is known to alter expression of sex steroids and to impair reproduction across vertebrates but the mechanisms underlying these effects are not clearly identified. We examined whether contamination by mercury predicts the probability to skip reproduction in black-legged kittiwakes (Rissa tridactyla) from Svalbard. We also manipulated the endocrine system to investigate the mechanism underlying this relationship. During the pre-laying period, we injected exogenous GnRH (gonadotropin-releasing hormone) to test the ability of the pituitary to release luteinizing hormone (LH, a key hormone for the release of sex steroids and hence breeding) in relation to mercury burden. Birds that skipped reproduction had significantly higher mercury concentration in blood than breeders. Endocrine profiles of these birds also varied based on breeding status (breeders versus non-breeders), mercury contamination and sex. Specifically, in skippers (birds that did not breed), baseline LH decreased with increasing mercury concentration in males, whereas it increased in females. GnRH-induced LH levels increased with increasing mercury concentration in both sexes. These results suggest that mercury contamination may disrupt GnRH input to the pituitary. Thus, high mercury concentration could affect the ability of long-lived birds to modulate their reproductive effort (skipping or breeding) according to ongoing environmental changes in the Arctic, thereby impacting population dynamics.
PMCID: PMC3730643  PMID: 23720523
intermittent breeding; mercury; GnRH challenge; luteinizing hormone; black-legged kittiwake
3.  Migratory constraints on yolk precursors limit yolk androgen deposition and underlie a brood reduction strategy in rockhopper penguins 
Biology Letters  2012;8(6):1055-1058.
Hormonally mediated maternal effects link maternal phenotype and environmental conditions to offspring phenotype. The production of lipid-rich maternal yolk precursors may provide a mechanism by which lipophilic steroid hormones can be transported to developing yolks, thus predicting a positive correlation between yolk precursors in mothers and androgen levels in eggs. Using rockhopper penguins (Eudyptes chrysocome), which produce a two-egg clutch characterized by extreme egg-size dimorphism, reversed hatching asynchrony and brood-reduction, we examined correlations between circulating concentrations of the primary yolk-precursor vitellogenin (VTG) and levels of yolk androgens. Previous work in Eudyptes penguins has shown that egg-size dimorphism is the product of migratory constraints on yolk precursor production. We predicted that if yolk precursors are constrained, androgen transport to developing yolks would be similarly constrained. We reveal positive linear relationships between maternal VTG and androgens in small A-eggs but not larger B-eggs, which is consistent with a migratory constraint operating on the A-egg. Results suggest that intra-clutch variation in total yolk androgen levels depends on the production and uptake of yolk precursors. The brood reduction strategy common to Eudyptes might thus be best described as the result of a migratory constraint.
PMCID: PMC3497107  PMID: 22809718
androstenedione; testosterone; physiological epiphenomenon hypothesis; vitellogenin; maternal effects; carryover effects
4.  Why do some adult birds skip breeding? A hormonal investigation in a long-lived bird 
Biology Letters  2011;7(5):790-792.
Skipping reproduction is often observed in long-lived organisms, but proximate mechanisms remain poorly understood. Since young and/or very old snow petrels (Pagodroma nivea) commonly skip breeding, we tested whether they are physiologically able to breed during the pre-laying stage. To do so, we measured the ability of known-age (11–45 years old) petrels to release luteinizing hormone (LH, a crucial driver for breeding), by injecting exogenous gonadotropin-releasing hormone (GnRH). Although young petrels exhibited low baseline LH levels, they were able to elevate LH levels after a GnRH challenge. Moreover, young and very old petrels showed a stronger decrease in LH levels after the 10 min post-GnRH injection compared with middle-aged petrels. Birds that skipped breeding were as able as breeders to release LH after a GnRH challenge, indicating that they had functional pituitaries. However, the decision to skip reproduction was linked to a strong LH decrease after the 10 min post-GnRH injection. Our result suggests that the youngest and the oldest petrels fail to maintain elevated baseline LH levels, thereby do not initiate reproductive activities. Skipping reproduction in long-lived birds probably results from age-related changes in the dynamics of the hypothalamic–pituitary–gonadal (HPG) axis function.
PMCID: PMC3169054  PMID: 21508027
intermittent breeding; age; GnRH challenge; luteinizing hormone; snow petrels
5.  Yolk androgen deposition without an energetic cost for female rockhopper penguins: a compensatory strategy to accelerate brood reduction? 
Biology Letters  2011;7(4):605-607.
Whether androgen deposition in eggs is physiologically costly for female birds has remained a crucial but unsolved question, despite a broad use of this assumption in functional studies. We tested whether females depositing high androgen concentrations experienced higher mass losses than females depositing low androgen concentrations. Analysing female body mass change during egg formation in rockhopper penguins (Eudyptes chrysocome chrysocome), we observed no energetic cost to androgen deposition. Nevertheless, lighter females laid eggs with higher yolk androgen concentrations. This relationship existed only for the second-laid egg (B-egg), but not for the first-laid egg (A-egg). Since the B-egg is usually the first to hatch and the only one to produce a fledging chick, we hypothesize that differential yolk androgen deposition may be an adaptive strategy for females to affect brood reduction.
PMCID: PMC3130214  PMID: 21325311
yolk testosterone; yolk androstenedione; female body mass; laying order
6.  Hormonal correlates of individual quality in a long-lived bird: a test of the ‘corticosterone–fitness hypothesis’ 
Biology Letters  2010;6(6):846-849.
Measuring individual quality in vertebrates is difficult. Focusing on allostasis mechanisms may be useful because they are functionally involved in the ability of an individual to survive and reproduce in its environment. Thus, a rise in stress hormones levels (corticosterone) occurs when an organism has to cope with challenging environmental conditions. This has recently led to the proposal of the ‘cort–fitness hypothesis’, which suggests that elevated baseline corticosterone levels should be found in individuals of poor quality that have difficulty coping with their environment. We tested this hypothesis by comparing an integrative measure of individual quality to baseline corticosterone in black-browed albatrosses (Thalassarche melanophrys). We found that individual baseline corticosterone levels were related to individual quality and highly repeatable from one breeding season to the next. Importantly, this relationship was found in males, but not in females. Therefore, we suggest that the relationship between quality and baseline corticosterone levels may depend on the environmental and energetic constraints that individuals have to cope with.
PMCID: PMC3001372  PMID: 20573614
corticosterone; fitness; quality; albatross
7.  Mhc polymorphisms fail to explain the heritability of phytohaemagglutinin-induced skin swelling in a wild passerine 
Biology Letters  2009;5(6):784-787.
Genetic estimates of the variability of immune responses are rarely examined in natural populations because of confounding environmental effects. As a result, and because of the difficulty of pinpointing the genetic determinants of immunity, no study has to our knowledge examined the contribution of specific genes to the heritability of an immune response in wild populations. We cross-fostered nestling house sparrows to disrupt the association between genetic and environmental effects and determine the heritability of the response to a classic immunological test, the phytohaemagglutinin (PHA)-induced skin swelling. We detected significant heritability estimates of the response to PHA, of body mass and tarsus length when nestlings were 5 and 10 days old. Variation at Mhc genes, however, did not explain a significant portion of the genetic variation of nestling swelling to PHA. Our results suggest that while PHA-induced swelling is influenced by the nest of origin, the importance of additive genetic variation relative to non-additive genetic variation and the genetic factors that influence the former in wild populations still need to be identified for this trait.
PMCID: PMC2827992  PMID: 19671600
major histocompatibility complex; phytohaemagglutinin-induced skin swelling; cross-fostering; heritability; house sparrow

Results 1-7 (7)