[Show abstract][Hide abstract] ABSTRACT: The stimulatory effect of testosterone on male sexual activity is one of the clearest examples linking hormones and behaviors. However, this relationship is complex in Chelonians. We experimentally studied the influence of testosterone levels on the activity budget and space use in male Greek tortoises (Testudo graeca graeca) during the spring mating season. We first described the annual pattern of changes in plasma testosterone levels in free-ranging animals in Morocco. Two peaks, one in winter and one in summer, corresponded to periods of inactivity; whereas mating periods in spring and to a lesser extent in autumn were associated with low plasma testosterone levels. Second, we experimentally manipulated plasma testosterone levels in free-ranging males, and analyzed the behavioral consequences. The strong contrasts in plasma hormone levels induced by the experimental treatments did not result in changes in activity budget or space use, both in the short-term or more than one month after the beginning of the hormonal treatment. Our results suggest that testosterone levels did not influence directly behavioral activity in this species, either immediately or after a time delay of one month.
General and Comparative Endocrinology 03/2010; 167(2):181-9. · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Female birds deposit corticosterone into their eggs. Elevated concentrations of this hormone may interfere with the development of their offspring, and mothers should thus regulate corticosterone levels deposited into the eggs adaptively. However, if females are unable to regulate deposition, then the corticosterone concentration in eggs should reflect that in female plasma and should be influenced by stressors to the females. We measured corticosterone levels in the albumen of rockhopper penguins, and assessed their relationship with hatching order, human disturbance and laying date. Rockhopper penguins (Eudyptes chrysocome chrysocome) lay two eggs, of which the second egg (B-egg) is larger and hatches faster than the first egg (A-egg). The chick hatching from the B-egg is also much more likely to survive than its sibling. Albumen corticosterone concentrations were lower in B-eggs. However, as B-eggs contained more albumen than A-eggs, the total corticosterone deposited in the albumen was not significantly different between the two eggs. Daily disturbance by human observers during albumen production did not influence albumen corticosterone levels. Laying date had an effect on total albumen corticosterone through a higher albumen mass. However, we observed a high individual component in the composition of eggs from the same clutch. Thus, more work is required to explore the hypotheses of passive versus active transfer to eggs and to understand the adaptive value of contrary effects on the amount and concentration of corticosterone.
General and Comparative Endocrinology 04/2009; 162(2):139-45. · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Because hormones mediate physiological or behavioral responses to intrinsic or extrinsic stimuli, they can help us understand how animals adapt their foraging decisions to energetic demands of reproduction. Thus, the hormone corticosterone deserves specific attention because of its influence on metabolism, food intake and locomotor activities. We examined the relationships between baseline corticosterone levels and foraging behavior or mass gain at sea in a diving seabird, the Adélie penguin, Pygoscelis adeliae. Data were obtained from free-ranging penguins during the brooding period (Adélie Land, Antarctica) by using satellite transmitters and time-depth-recorders. The birds were weighed and blood sampled before and after a foraging trip (pre-trip and post-trip corticosterone levels, respectively). Penguins with elevated pre-trip corticosterone levels spent less time at sea and stayed closer to the colony than penguins with low pre-trip corticosterone levels. These short trips were associated with a higher foraging effort in terms of diving activity and a lower mass gain at sea than long trips. According to previous studies conducted on seabird species, these results suggest that penguins with elevated pre-trip corticosterone levels might maximize the rate of energy delivery to the chicks at the expense of their body reserves. Moreover, in all birds, corticosterone levels were lower post-foraging than pre-foraging. This decrease could result from either the restoration of body reserves during the foraging trip or from a break in activity at the end of the foraging trip. This study demonstrates for the first time in a diving predator the close relationships linking foraging behavior and baseline corticosterone levels. We suggest that slight elevations in pre-trip corticosterone levels could play a major role in breeding effort by facilitating foraging activity in breeding seabirds.
General and Comparative Endocrinology 04/2008; 156(1):134-44. · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Competitive stress imposed by hatching asynchrony may affect developmental trajectories of offsprings by regulating resource allocation between growth and other fitness-related traits. For instance, the down-regulation of immunity is a commonly observed phenomenon under stressful conditions. However, physiological mechanisms that regulate resources allocation to growth and immune functions in response to competition for resources, as well as inter-sexual differences in physiological strategies, are still poorly investigated. To partially fill this gap, we first conducted a descriptive study on chicks of the collared dove (Streptopelia decaocto), a species producing two chicks per brood. Our results show that first hatchlings (seniors) were bigger, showed lower baseline corticosterone levels (CORT) and showed a higher cell-mediated immunoresponsiveness (CMI) than late hatchlings (juniors). However, when controlling for body size, only CMI remained weaker in junior chicks suggesting differences in strategies of resource allocation between siblings. Interestingly, CORT in juniors increased with increasing within-brood hierarchy. But, while within-brood variation in CMI followed the opposite pattern of variation in CORT, we found no evidence that inter-individual variation in CMI was directly related to CORT. In addition hatching-rank related differences in body size, CMI and CORT was similar between sexes. To ensure that the lower phenotypic value expressed by juniors was not fully related to a lower quality of the late-laid egg, we experimentally suppressed the competitive stress experienced by juniors by removing the first-laid egg (i.e. the egg normally producing a senior chick). In the absence of their brood mates, juniors were bigger, had lower levels of CORT and showed a higher CMI than juniors raised in two-brood chicks, suggesting that body size, CMI and CORT in juniors were modulated by the competitive stress. Overall, this study suggests that juniors respond to within-brood competition by elevating CORT and down-regulating CMI. In this context, the role of CORT, as a mechanism regulating physiological strategies related to growth and immunocompetence is discussed.
General and Comparative Endocrinology 03/2008; 155(3):542-51. · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Begging is a complex display that is supposed to honestly indicate the need for food of nestlings, and, usually, parents use this information to adjust their investment in food provisioning. However, the mechanisms that ensure the honesty of begging as an indicator of need are still poorly known. It has been shown that levels of corticosterone (Cort), the hormone released during the stress response, raises during food shortage and is associated with increased begging rate. However, Cort also entails costs and these costs might prevent nestlings cheating. We tested this hypothesis in nestlings of the house sparrow. We experimentally increased levels of circulating Cort and investigated (1) the behavioral responses of nestlings, (2) the parental allocation of food and (3) the consequences on nestling growth and immune response. We found that Cort significantly increased begging rate but did not affect posture and position in the nest. Surprisingly, when begging effort was controlled statistically, control nestlings received more food from parents than Cort-treated nestlings. We also found that nestlings injected with Cort showed a weaker immune response and had lower body mass than controls. We suggest that Cort might have affected multiple aspects of nestling signaling, such as mouth color, and that parents use these multiple signals to adjust their feeding effort.
General and Comparative Endocrinology 02/2008; 155(1):101-8. · 2.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The ultimate factors influencing age-specific reproductive performance in birds have been widely discussed, and several hypotheses
have been suggested to explain why young/inexperienced breeders have lower reproductive success than older individuals. In
comparison, proximate factors and, particularly, hormonal mechanisms influencing age-related reproductive performance have
received lesser attention. In this paper, we examined how baseline levels of corticosterone and prolactin, two hormones involved
in reproduction, changed with age and experience in a long-lived bird, the Black-browed albatross (Thallasarche melanophris) during the brooding stage. Corticosterone levels were not linked to age, whereas prolactin levels increased until individuals
reached 15years of age. First-time breeders had higher corticosterone levels and lower prolactin levels than experienced
ones. Corticosterone levels were not correlated with breeding experience among experienced birds, whereas prolactin levels
slightly increased with advancing experience. Among experienced breeders, there was no effect of individual quality on corticosterone
and prolactin levels. Baseline corticosterone and prolactin levels were respectively, positively and negatively correlated
to time spent fasting/brooding on the nest. Moreover, the probability of successfully fledging a chick was negatively related
to corticosterone levels, but not to prolactin levels. Elevated corticosterone levels in first time breeders may serve as
evidence for depleted body reserves resulting from lower foraging/brooding capabilities and therefore support the constraint
hypothesis. Low prolactin levels in young/inexperienced birds may be interpreted either as evidence for their lower breeding
capacities (constraint hypothesis) or for their limited breeding investment (restraint hypothesis). Finally, we report, for
the first time, the hormonal changes associated with the onset of senescence. The very old and most experienced birds, which
had the lowest probability of successfully fledging a young, displayed elevated corticosterone levels and low prolactin levels,
possibly indicating a degradation of breeding skills and/or a disruption of the endocrine system in senescent birds.
Behavioral Ecology and Sociobiology 01/2007; 61(4):611-621. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sex ratio theory is one of the most controversial topics in evolutionary ecology. Many deviations from an equal production
of males and females are reported in the literature, but few patterns appear to hold across species or populations. There
is clearly a need to identify fitness effects of sex ratio variation. We studied this aspect in a population of a long-lived
seabird, the wandering albatross (Diomedea exulans), using molecular sex-identification techniques. We report that parental traits affect both (1) fledgling traits in a sex-dependent
way and (2) chick sex: Sons are overproduced when likely to be large at fledging and, to a lesser extent, daughters are overproduced
when likely to be in good body condition at fledging. Because for the same population, a previous study reported that post-fledging
survival was positively affected by size in males and by body condition in females, our results suggest that wandering albatrosses
manipulate offspring sex to increase post-fledging survival.
Behavioral Ecology and Sociobiology 01/2007; 61(5):767-773. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The genus Pseudobulweria includes four extant species, three being classified as critically endangered, while the fourth (Tahiti Petrel P. rostrata) is near threatened. Information on the breeding biology of any species of the genus is scarce, even for the Tahiti Petrel. We monitored two Tahiti Petrel nests in New Caledonia and provide the first data on the breeding biology for the genus. Incubation lasts about 55 days, and young fledge at 110 days. Breeding in the southern lagoon of New Caledonia extends from September to April. Very strong interspecific competition for nest cavities occurs with Wedge-tailed Shearwaters Puffinus pacificus. We also document geographical variation in both biometry and breeding phenology over the Pacific breeding range.