Novel energy savings to multiple stressors in birds: The ultradian regulation of body temperature

This study aimed to examine thermoregulatory responses in birds facing two commonly experienced stressors, cold and fasting. Logging devices allowing long-term and precise access to internal body temperature were placed within the gizzards of ducklings acclimated to cold (CA) (5°C) or thermoneutrality (TN) (25°C). The animals were then examined under three equal 4-day periods: ad libitum feeding, fasting and re-feeding. Through the analysis of daily as well as short-term, or ultradian, variations of body temperature, we showed that while ducklings at TN show only a modest decline in daily thermoregulatory parameters when fasted, they exhibit reduced surface temperatures from key sites of vascular heat exchange during fasting. The CA birds, on the other hand, significantly reduced their short-term variations of body temperature while increasing long-term variability when fasting. This phenomenon would allow the CA birds to reduce the energetic cost of body temperature maintenance under fasting. By analysing ultradian regulation of body temperature, we describe a means by which an endotherm appears to lower thermoregulatory costs in response to the combined stressors of cold and fasting

Stratégies de tolérance au froid chez les ectothermes hivernants (études physiologiques sur Lacerta vivipara et approche théorique globale)

Les vertébrés ectothermes ont développé deux stratégies de tolérance au froid leur permettant de survivre aux contraintes thermiques imposées par l'hiver : la tolérance au gel et l'évitement au gel (par l'augmentation des capacités de surfusion). Cette étude s'articule sur deux axes principaux. D'une part, je me suis attaché à approfondir les connaissances physiologiques de tolérances au froid d'un vertébré ectotherme européen : le lézard vivipare (Lacerta vivipara) dont la répartition géographique dépasse le cercle polaire arctique et qui possède la capacité rare d'utiliser les deux stratégies au cours d'un même hiver. Les résultats apportent des éléments de compréhension quant à la balance métabolique de cet animal pendant l'hiver, sa tolérance au gel (la plus importante parmi les squamates et son métabolisme aérobie en état de surfusion et de congélation. Je me suis ensuite attaché à intégrer les stratégies de tolérance au froid dans un contexte plus écologique et évolutionniste. Afin d'apporter une tentative d'explication quant aux existence des stratégies, un modèle d'optimisation de fitness a été développé en tenant compte de différents paramètres physiologiques (comme les réserves énergétiques et le stress associé à chaque stratégie) et les conditions environnementales (température et nombre de jours de froid). Les résultats théoriques, discutés à la lumière de données physiologiques concernant différentes espèces d'ectothermes, permettent d'émettre des prédictions quant à l'influence de la physiologie dans l'évolution des stratégies de tolérance au froid des ectothermes et suggèrent des voies d'expérimentations, principalement liées à l'influence du stress sur l'évolution des stratégies.LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Male within-individual variability in a sexual signal component and its impact on female choice

International audienceA growing body of literature deals with the influence of physical or social environments on signal components over long time periods. Surprisingly, variations of signal quality over minutes or hours are less studied although most of the behavioral decisions of the receiver are taken at this time scale. Despite potentially strong implications on theoretical developments linked to sexual selection and communication, within-individual variability in a signal component and its possible consequence on accuracy of female choice has never been thoroughly investigated. Focusing on call dominant frequency (DF) in the European tree frog, Hyla arborea, we showed that frequency variability is due to a warm-up effect on the beginning of the call sequence but not to an exhaustion effect at the end of the sequence. Nevertheless, the great majority of male within-variability at the night scale is due to sudden discontinuities with independent temporal patterns from one individual to another. Secondly, we simulated female mate choice decisions with simple rules based on DF. Within-individual variability in DF the proportion of beneficial choice decreases up to 30% in the worst case. In addition, to overcome these temporary variations in male signal, we emphasize a weak advantage supplied by increasing sampling duration. The costs of being selective are assumed to increase with time sampling. We suggest that females may benefit from assessing several signal components simultaneously in short samples instead of disproportionately increasing sampling duration

Physiological actions of corticosterone and its modulation by an immune challenge in reptiles

International audienceHormones are an important interface between genome and environment, because of their ability to modulate the animal's phenotype. In particular, corticosterone, the stress hormone in lizards, is known to reallocate energy from non-essential functions to affect morphological, physiological and behavioral traits that help the organism to deal with acute or chronic stressors. However, the effects of corticosterone on life history stages are still unclear primarily because of the dependence of life history stages on both internal and external factors. Using a cross-design, we tested the effect of elevated levels of exogenous corticosterone on the physiology of pregnant females in different immune contexts in a wild population of common lizards (Lacerta vivipara). Immune challenge was induced by the injection of sheep red blood cells (SRBC) and corticosterone levels were increased using a transdermal administration of corticosterone. Thereafter, reproductive traits, metabolism and cellular immune responses were measured. The elevation of corticosterone in pregnant females significantly altered reproductive and physiological performance. The corticosterone treatment decreased clutch success, juvenile size and body condition, but enhanced measures of physiological performance, such as metabolism and catalase activity. These first results reinforce the understanding of the physiological actions of corticosterone in reptiles. The data also demonstrated different direct impacts of immune challenge by SRBC on inflammatory response and antioxidant activity. The injection of SRBC stimulated the SOD activity in larger females. Finally, we demonstrated experimentally the modulation of the corticosterone action by the immune challenge on stamina and hatching date. Copyright @ 2010 Elsevier Inc. All rights reserved

The proximal costs of case construction in caddisflies: antioxidant and life history responses

International audienceAnimal construction allows organisms to cope with environmental variations but the physiological costs of such behaviour are still poorly understood. The aim of the present study was to measure the physiological cost of construction behaviour through the oxidative balance that is known to affect the ability of organs to function, stimulates senescence processes and ultimately impacts the fitness of the organism. We used larvae of caddisfly, Limnephilus rhombicus, by experimentally modifying the effort associated with case building. Larvae that were forced to build a new case showed a significant increase in both total antioxidant capacity and the specific activity of superoxide dismutase 48 and 72 h, respectively, after the initiation of the reconstruction. These results strongly suggest that the larval construction behaviour triggered the production of reactive oxygen species, but their effects were reversed 7 days after the reconstruction. In the animals that were forced to build a new case, oxidative stress appeared to be mitigated by a network of antioxidant defences because no oxidative damage was observed in proteins compared with the control larvae. At the adult stage, while longevity was not sex dependent and was not affected by the treatment, body mass and body size of adult males from the reconstruction treatment were significantly lower than the control values. This unexpected sex effect together with data on oxidative stress highlights the difficulty of determining the physiological cost associated with energy-demanding behaviours, implying a consideration of both their energetic and non-energetic components is required

Body mass dependence of oxidative phosphorylation efficiency in liver mitochondria from mammals

International audienceIn eukaryotes, the performances of an organism are dependent on body mass and chemically supported by the mitochondrial production of ATP. Although the relationship between body mass and mitochondrial oxygen consumption is well described, the allometry of the transduction efficiency from oxygen to ATP production (ATP/O) is still poorly understood. Using a comparative approach, we investigated the oxygen consumption and ATP production of liver mitochondria from twelve species of mammals ranging from 5 g to 600 kg. We found that both oxygen consumption and ATP production are mass dependent but not the ATP/O at the maximal phosphorylating state. The results also showed that for sub-maximal phosphorylating states the ATP/O value positively correlated with body mass, irrespective of the metabolic intensity. This result contrasts with previous data obtained in mammalian muscles, suggesting a tissue-dependence of the body mass effect on mitochondrial efficiency