Abstract: Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life-history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life-history trade-offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life-history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state-dependent variation in life-history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non-breeding birds. Using a 50-year dataset on the long-lived quasi-biennial breeding wandering albatross, we investigated variations in life-history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non-breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi-biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade-offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its relationship with costs of reproduction at the population level. It paves the way for individual-based studies that could show the importance of intra-population heterogeneity in those processes.

Abstract:

One of the thematic set of questions of the SCAR first Horizon Scan deals with the impact of human presence on the Antarctic environment and wildlife. Questions 74 (How can natural and human-induced environmental changes be distinguished, and how will this knowledge affect Antarctic governance?) and 75 (What will be the impacts of large-scale, direct human modification of the Antarctic environment?) represent pressing issues that still lack scientific data to be addressed, despite investigations conducted in the Peninsula region where human presence is more acute than elsewhere. In addition, impact studies on wildlife, especially upper vertebrates, are often confined to observational studies, possibly masking underlying physiological responses of wildlife to human exposure. In this context, our study aimed at examining the physiological response of Adélie penguins (Pygoscelis adeliae) from Terre Adélie, East Antarctica, to various degrees of long-term human exposure using a standardized stress protocol. When exposed to stressors, a hormonal stress response is indeed activated to shift energy investment away from reproduction and/or growth and to redirect it towards immediate survival. In vertebrates, this stress response is achieved through a release of glucocorticoids hormones (corticosterone in birds). One of the most common method to measure such a hormonal response, is to subject individual to a standardized capture/restraint/stress protocol. In our experiment, two sites with sustained and continuous human activity (on Petrels Island where the scientific base of Dumont d'Urville is installed since 1952) were opposed to two sites on neighbouring islands with little or no human activities (Island Lamarck and Bernard). Stress response experiments were conducted on fifteen adults per site from nests with equal value (2 eggs or 2 chicks per nests) several times during the reproductive season, on incubating females, incubating males, chick-rearing males and females. Around 15 large chicks were also tested per site. Within 0 to 3 minutes after capture, an initial blood sample was collected to measure baseline corticosterone levels. Birds were then restrained for ca. 15 minutes and a subsequent sample was collected to measure maximum stress-induced corticosterone levels. We expected birds from sites with little human impact to present greater elevation in corticosterone concentration following restraint. Although we do not want to spoil the results in this abstract we can tell that the story has a – probably counter-intuitive – happy-ending, bringing valuable information for the Standing Committee on the Antarctic Treaty System to develop scientific advice to the Antarctic Treaty Consultative on this hot topic.

Abstract: Life-history theory predicts that individuals should adapt their parental investment to the costs and benefits of the current reproductive effort. This could be achieved by modulating the hormonal stress response, which may shift energy investment away from reproduction and redirect it toward survival. In birds, this stress response consists of a release of corticosterone that may be accompanied by a decrease in circulating prolactin, a hormone involved in the regulation of parental care. We lack data on the modulation of the prolactin stress response. In this study, we tested the hypothesis that individuals should modulate their prolactin stress response according to the fitness value of the current reproductive effort relative to the fitness value of future reproduction. Specifically, we examined the influence of breeding status (failed breeders vs. incubating birds) and body condition on prolactin and corticosterone stress responses in a long-lived species, the snow petrel Pagodroma nivea. When facing stressors, incubating birds had higher prolactin levels than failed breeders. However, we found no effect of body condition on the prolactin stress response. The corticosterone stress response was modulated according to body condition but was not affected by breeding status. We also performed an experiment using injections of adrenocorticotropic hormone (ACTH) and found that the modulation of the corticosterone stress response was probably associated with a reduction in ACTH release by the pituitary and a decrease in adrenal sensitivity to ACTH. In addition, we examined whether prolactin and corticosterone secretion were functionally linked. We found that these two hormonal stress responses were not correlated. Moreover, injection of ACTH did not affect prolactin levels, demonstrating that short-term variations in prolactin levels are not governed directly or indirectly by ACTH release. Thus, we suggest that the corticosterone and prolactin responses to short-term stressors are independent and may therefore mediate some specific components of parental investment in breeding birds. With mounting evidence, we suggest that examining both corticosterone and prolactin stress responses could be relevant to parental investment in vertebrates.

Abstract: La compétition spermatique
est souvent associée à des testicules plus volumineux chez un grand nombre de
taxa. Les mêmes prédictions ont été faites chez les mammifères mais les données
empiriques sont peu nombreuses et les résultats ne sont pas toujours conformes
aux attendus. Alternativement, en situation de compétition spermatique exceptionnellement
intense chez une espèce, les modèles de théorie des jeux suggèrent qu'il
devrait y avoir une sélection en faveur d'une diminution de la quantité de sperme
transféré, qui pourrait sélectionner une diminution de la taille des testicules.
De plus, les mâles devraient produire de faibles quantités de sperme en absence
de compétiteur, et les plus fortes quand il y a juste un compétiteur. Pour
examiner les prédictions de la théorie de la compétition spermatique et du
modèle d'intensité de Parker, nous avons comparé la taille relative des
testicules chez les mâles de 5 populations de chats domestiques (Felis catus L.) contrastées
par le niveau de compétition spermatique rencontré par les mâles. Comme prévu
par le modèle d'intensité de Parker, nous avons constaté que les mâles vivant
dans les populations rurales ont de plus gros testicules que ceux vivant dans
les environnements extrêmes (Kerguelen), où la compétition spermatique est la plus
faible, et que ceux vivant dans les populations urbaines, où la compétition spermatique
est plus forte.