It Costs to Be Clean and Fit: Energetics of Comfort Behavior in Breeding-Fasting Penguins

), seabirds known to fast for up to one month during incubation shifts ashore.A time budget was estimated from focal and scan sampling field observations and the energy cost of comfort activities was calculated from the associated increase in heart rate (HR) during comfort episodes, using previously determined equations relating HR to energy expenditure. We show that incubating birds spent 22% of their daily time budget in comfort behavior (with no differences between day and night) mainly devoted to preening (73%) and head/body shaking (16%). During comfort behavior, energy expenditure averaged 1.24 times resting metabolic rate (RMR) and the corresponding energy cost (i.e., energy expended in excess to RMR) was 58 kJ/hr. Energy expenditure varied greatly among various types of comfort behavior, ranging from 1.03 (yawning) to 1.78 (stretching) times RMR. Comfort behavior contributed 8.8–9.3% to total daily energy expenditure and 69.4–73.5% to energy expended daily for activity. About half of this energy was expended caring for plumage.This study is the first to estimate the contribution of comfort behavior to overall energy budget in a free-living animal. It shows that although breeding on a tight energy budget, king penguins devote a substantial amount of time and energy to comfort behavior. Such findings underline the importance of comfort behavior for the fitness of colonial seabirds

Flux lipolytiques et jeûne prolongé chez le manchot royal

Ce travail a pour but l'étude des flux lipolytiques et de leur régulation, et des interactions entre substrats métaboliques in vivo lors du jeûne prolongé, et particulièrement au passage phase II-phase III, dans des conditions environnementales naturelles chez le manchot royal. Ce travail montre que: Malgré l'état critique (mais non total) d'épuisement des réserves lipidiques lors de la phase III: -la production des acides gras non-estérifiés (AGNE) par le tissu adipeux et la disponibilité plasmatique des AGNE ne sont pas diminuées. La disponibilité plasmatique des AGNE pour les voies oxydatives n'est pas proportionnelle à la taille des réserves lipidiques (article1). -la réponse lipolytique au glucagon est maintenue. La sensibilité lipolytique du tissu adipeux au glucagon n'est pas affectée par la diminution de la taille des cellules adipeuses (article 2). Lors de la phase II du jeûne, une inhibition de l'oxydation des AGNE, par perfusion de mercaptoacétate, simule les changements métaboliques et hormonaux marquant le passage phase II-phase III (article 3). Ces résultats soutiennent l'hypothèse que le passage phase II-phase III et la stimulation du comportement alimentaire qui y est associée, sont induits par une réduction de l'oxydation des AGNE, indépendante de leur disponibilité. Ce travail suggère aussi que lors du jeûne prolongé: - le métabolisme des protéines n'est pas modulé par la seule disponibilité des AGNE, mais dépend de leur oxydation. - la corticostérone est le lien entre l'oxydation des AGNE et le catabolisme des protéines. -la disponibilité du glucose contrôle la composition du mélange de substrats qui est oxydé pour la production d'énergie (article 4). Ce contrôle dépend de l'état métabolique et hormonal (ex, stressés vs non-stressés) des animaux.The aim of this work is to study in vivo, the lipolytic fluxes, their regulation, and substrate interactions in prolonged fasting king penguins in their natural environment. It particularly focuses on the phase II-phase III transition. This work shows that: In phase III of fasting, the production of non-esterified fatty acids (NEFA) by the adipose tissue and the plasma availability of NEFA are not decreased, despite the critical (but still incomplete) exhaustion of fat stores. Plasma NEFA availability for oxidation is not directly proportional to the size of fat stores (article 1). Lipolytic response to glucagon is also maintained at this state of fasting. The lipolytic sensitivity of adipose tissue to glucagon is not lowered as fat cell size decreases (article 2). In phase II of fasting, an inhibition of fatty acid oxidation (induced by mercaptoacetate) mimics the metabolic and hormonal changes characterizing the phase II-phase III transition (article 3). These results support the hypothesis that a reduction in NEFA oxidation, independent of their availability induces the entrance into phase III and the associated stimulation of feeding behavior. This work also suggests that during prolonged fasting: - Protein metabolism is related to NEFA oxidation and not only by the availability of these fuels. - Corticosterone constitutes a link between NEFA oxidation and protein metabolism. - The availability of glucose is an important determinant of the substrate mix that is oxidized for energy production (article 4). This control depends on the metabolic and/or hormonal status (i.e. stressed vs. non-stressed) of the animals.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Envol chez le poussin d'oiseau (Rôle de l'investissement parental et mécanismes proximaux)

L envol du jeune oiseau est une transition vers l autonomie locomotrice et alimentaire. L état physique doit alors être optimisé pour limiter les risques accrus de mortalité par prédation ou par famine. Cet état est largement dépendant de l investissement parental lequel fait l objet d un conflit entre parents et petits.Mon travail de thèse s attache à comprendre les mécanismes proximaux retenus chez l oiseau pour optimiser le phénotype à l envol. Deux espèces à l écologie contrastée ont été comparées: le Manchot royal (MR; Aptenodytes patagonicus) et la Cigogne blanche (CB; Ciconia ciconia).Chez le MR, l accumulation de réserves lipidiques dans la progéniture permet à l éleveur de déserter et d initier la mue prénuptiale tout en assurant la fin de la croissance du poussin à jeun. De plus, ces réserves préviennent une activation de l axe hypothalamo-hypophyso-corticosurrénalien (HHCS) et un catabolisme exacerbé des protéines, lequel menacerait l intégrité musculaire du poussin. Chez la CB, la restriction alimentaire parentale induit chez les cigogneaux un stress nutritionnel qui active l axe HHCS et la sécrétion de corticostérone. La corticostéronémie élevée stimulerait les exercices locomoteurs au nid et par là faciliterait l envol. La hiérarchie de développement au sein de la nichée modulerait la sensibilité de l axe HHCS, ce qui préviendrait les effets délétères d une corticostéronémie chroniquement élevée sur la croissance alaire des derniers éclos.Mes résultats permettent de proposer de nouvelles hypothèses quant aux pressions sélectives exercées sur 1) l accumulation des réserves lipidiques et 2) la sécrétion de corticostérone chez le poussin en fin de croissance.Fledging in birds is a transition from a situation in which it is totally dependent on its parents to a self-sufficient life. Physical state should be optimized at fledging to face increased predation and starvation risks outside the nest. Physical state at fledging is largely dependent on parental investment, over which parents and offspring disagree.My Ph.D work aims at understanding the proximate mechanisms that optimize phenotype at fledging. I used a comparison between two avian species with markedly different ecology: the King penguin (KP, Aptenodytes patagonicus) and the White stork (WS; Ciconia ciconia). In KP, parents accumulate important lipid stores in chicks before deserting and starting prenuptial moult. Lipid stores in deserted, fasting chicks fuel the completion of growth. Lipid stores also prevent the activation of the Hypothalamic-Pituitary-Adrenal (HPA) axis and associated increased catabolism of muscular proteins in chicks. In WS, parental food restriction results in a nutritional stress which activates the HPA axis and corticosterone release in chicks. High plasma levels of corticosterone stimulate flight-training activity and hence facilitate fledging. The down-regulation of the HPA axis in last-hatched chicks prevents the impairment of wing growth due to chronically elevated plasma levels of corticosterone. The results of my work are discussed and shed new light on the evolutionary forces that shape 1) fattening and 2) corticosterone release in prefledging birds.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Compromis entre alimentation et risque de prédation chez les canards hivernants (Une approche multi-échelles)

Les stratégies comportementales réalisées par les canards de surface hivernants (colvert Anas platyrhynchos et sarcelle d hiver A.crecca) en fonction des ressources et du risque de prédation ont été étudiées sur trois sites: l estuaire de la Seine, le marais de Moëze-Oléron et les étangs de Brenne. Les décisions d alimentation dépendent étroitement de la densité de ressources présente avec l existence d une densité critique à 15 g/m . Le pâturage ou la tonte vont diminuer le stock de graines disponible et influencer la capacité d accueil. Le suivi d individus équipés d émetteurs aura permis de montrer que la décision de quitter les zones protégées pour s alimenter sur des zones plus risquées (chassées) est fonction de la taille des individus. Le marquage de colverts d élevage lâchés en Brenne aura permis de montrer que la pression de chasse est la cause principale de mouvement où les individus de plus petite taille vont quitter leur lieu de lâcher et ainsi augmenter leur survie.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Ajustements aux contraintes énergétiques et sociales chez un reproducteur colonial, le manchot royal (Aptenodytes patagonicus)

Cette thèse s intéresse aux stratégies comportementales et physiologiques permettant à un oiseau colonial, le manchot royal, de se reproduire sous de fortes contraintes énergétiques (jeûne prolongé) et sociales (forte densité de congénères) potentiellement stressantes. Utilisant la fréquence cardiaque (FC) comme indicateur de la dépense énergétique et de la réponse au stress, elle considère : 1) le coût énergétique des comportements majeurs (confort et agressivité) du manchot royal se reproduisant à terre, questionnant leur signifiance évolutive; 2) les changements physiologiques (FC, température corporelle, activité physique) associés au jeûne reproductif le plus long (1 mois), révélant que la FC de repos des animaux est fortement influencée par la densité coloniale et suggérant un coût énergétique de la vie en groupe; 3) L influence de l environnement social, indiquant que lors d'interactions agressives la réponse cardiaque des animaux est modulée par leur implication dans l'interaction et par le risque associé; 4) Les effets du statut nutritionnel et reproductif sur les réponses cardiaques, hormonales et métaboliques à différents stress anthropiques aigus, démontrant que ces réponses varient en fonction de la valeur relative de la reproduction (œuf vs. poussin). L atténuation de ces réponses, coûteuses en énergie et pouvant conduire à l'abandon de la progéniture, permettrait d augmenter le succès reproducteur lorsque la valeur de la reproduction en cours est élevée. Des recherches futures permettront de déterminer les conséquences physiologiques (coût énergétique, stress oxydatif, vieillissement) du stress social chez des espèces vivant en groupe.This thesis investigates the behavioral and physiological strategies that allow a colonial breeder, the king penguin (Aptenodytes patagonicus), to breed while fasting in a crowded, possibly stressful, social environment. First, by monitoring penguin heart rate (HR) as a proxy to energy expenditure, it considers the energy cost of the most common behaviors (comfort and aggressive behavior) of penguins breeding ashore, and questions the adaptive significance of high and low, respectively, energy investment into these two behaviours. Second, it investigates the physiological changes that occur during the longest breeding fast (1 month) by continuously recording HR, body temperature and physical activity in incubating males. It reveals that changes in colony density (i.e. crowding) may have a strong impact on the energy expended to fuel metabolism at rest, i.e. first evidence for an energy cost of group-living in birds. Third, it shows that penguins are highly sensitive to the social environment, as indicated by changes in HR responses to aggressive contexts of various relevance and associated risks. Fourth, it investigates the effects of breeding status on costly stress responses (hormonal, metabolic and cardiac). It shows that responses to acute stress decrease with increasing reproductive value of the offspring (egg vs. chick), suggesting that stress responses may be adaptively attenuated to improve breeding success and fitness, when reproductive value of the current reproduction is high. Further research is needed to investigate the physiological consequences (energy expenditure, oxidative stress, aging) of social stress in group-living animals.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Breeding status affects the hormonal and metabolic response to acute stress in a long-lived seabird, the king penguin

International audienceStress responses are suggested to physiologically underlie parental decisions promoting the redirection ofbehaviour away from offspring care when survival is jeopardized (e.g., when facing a predator). Besidesthis classical view, the ‘‘brood-value hypothesis” suggests that parents’ stress responses may be adaptivelyattenuated to increase fitness, ensuring continued breeding when the relative value of the broodis high. Here, we test the brood-value hypothesis in breeding king penguins (Aptenodytes patagonicus),long-lived seabirds for which the energy commitment to reproduction is high. We subjected birds atdifferent breeding stages (courtship, incubation and chick brooding) to an acute 30-min capture stressand measured their hormonal (corticosterone, CORT) and metabolic (non-esterified fatty acid, NEFA)responses to stress. We found that CORT responses were markedly attenuated in chick-brooding birdswhen compared to earlier stages of breeding (courtship and incubation). In addition, NEFA responsesappeared to be rapidly attenuated in incubating and brooding birds, but a progressive increase inNEFA plasma levels in courting birds suggested energy mobilization to deal with the threat. Our resultssupport the idea that stress responses may constitute an important life-history mechanism mediatingparental reproductive decisions in relation to their expected fitness outcom

Coping with social stress: heart rate responses to agonistic interactions in king penguins

International audienceIn colonial breeders, agonistic interactions between conspecifics are frequent and may have significant physiological implications. Physiological responses (e.g., increased heart rate) to such social stressors may be determined by the potential costs of agonistic interactions, such as personal injury or risk of breeding failure, and by the motivation of the individuals concerned. The latter may vary according to individuals' reproductive status or willingness to engage in agonistic interactions. In this study, we investigated heart rate responses to aggressive interactions in a breeding colony of king penguins Aptenodytes patagonicus. From heart rate (HR) and behavior recorded in 20 adults at various stages of the breeding season, we investigated how king penguins reacted to aggressive neighbors. A total of 589 agonistic interactions, 223 in which birds were actors and 366 in which birds remained bystanders (i.e., witnesses that were not involved in interactions), were characterized. We found that HR increased during agonistic interactions, both in actors and bystanders. The intensity (threat displays or physical attacks), duration, and rate of aggressive events (number of threats/blows per unit time) of an interaction significantly influenced the HR response in actors. For bystanders, however, only the duration of interactions seemed to matter. Our results also suggest a role for individual motivation, as initiators of agonistic interactions displayed higher HR increases than responders, and as increases were not constant throughout the reproductive season. We conclude that individual risk assessment and motivation modulate physiological responses to social stressors in group-living animal

Stress hormones in relation to breeding status and territory location in colonial king penguin: a role for social density?

Because glucocorticoid (stress) hormones fundamentally affect various aspects of the behaviour, life history and fitness of free-living vertebrates, there is a need to understand the environmental factors shaping their variation in natural populations. Here, we examined whether spatial heterogeneity in breeding territory quality affected the stress of colonial king penguin (Aptenodytes patagonicus). We assessed the effects of local climate (wind, sun and ambient temperature) and social conditions (number of neighbours, distance to neighbours) on the baseline levels of plasma total corticosterone (CORT) in 77 incubating and 42 chick-brooding birds, breeding on territories of central or peripheral colony location. We also assessed the oxidative stress status of a sub-sample of central vs. peripheral chick-brooders to determine whether chronic stress arose from breeding on specific territories. On average, we found that brooders had 55 % higher CORT levels than incubators. Regardless of breeding status, central birds experienced greater social density (higher number of neighbours, shorter distance between territories) and had higher CORT levels than peripheral birds. Increasing social density positively explained 40 % of the variation in CORT levels of both incubators and brooders, but the effect was more pronounced in brooders. In contrast, climate was similar among breeding territories and did not significantly affect the CORT levels of breeding birds. In brooders, oxidative stress status was not affected by local density or weather conditions. These results highlight that local heterogeneity in breeding (including social) conditions may strongly affect the stress levels of breeding seabirds. The fitness consequences of such variation remain to be investigated