Dr Agnès Lewden
I am an eco-physiologist specialized in bird energetics focusing on energy expenditure linked to muscle activity in a context of cold acclimatization and flight activity. Indeed, I previously worked on thermoregulation in cold condition with passerine wintering in Canada and penguin spending foraging trip in cold water and my new project aim to understand energy expenditure during flight activity.
I did my Masters at the University of Rimouski (Canada) in 2009. I studied the winter acclimatization in Black-capped chickadees (Poecile atricapillus L.) in free-living condition. I developed a keen interest for endotherm species living in cold conditions. Therefore, I have worked as a biologist for 15 months in the French scientific station "Dumont d’Urville" in Terre Adélie (Antarctica). Then, I completed my Ph.D degree under a three-year doctoral fellowship funded by the French Ministry of Education and Research studying the king penguin (Aptenodytes patagonicus) thermoregulation strategies and the energetic consequences.
Maintain a high stable temperature is crucial in endotherm species to permit at their organism to run optimally (cell multiplication, mitochondrial and enzymatic activity etc.) and respond to external as well as internal stimuli. My research aim to understand heat exchange regulation between organism and environment but also within an organism (i.e. heterothermia) and the energetic consequences of the body/tissues temperature variations.
To study this, I measured different parameters in free-ranging and captive birds: surface temperatures/heat dissipation using non-invasive thermal imaging, sub-cutaneous and internal temperatures using implanted loggers, metabolic rate using respirometry chain, body acceleration using accelerometry and heart rate frequency.
Bird flight energetics (2018-...)
Flapping flight is particularly energetically demanding exhibiting the highest rates of energy expenditure of any mode of locomotion (Norberg 1990 – Animal Flight). However, many of the techniques used to study avian aerodynamics, biomechanics and energetics within a laboratory setting are not easily transferrable into the field. The aim of this project with Dr Graham Askew (University of Leeds) and Dr Charles Bishop (Bangor University) is to understand how indirect proxies of flight energetics can best act as indicators of metabolic rate and avian biomechanical flight performance to be able to increase our acknowledgments in bird’s flight energetic in wild condition.
King penguin (Aptenodytes patagonicus) thermoregulation in cold water (2012-...)
The energetic cost of foraging activities in King Penguin consists to reach favorable areas, realizes depth diving to attempt fish patch and resting in high latitude cold water. Several studies have shown that resting in cold water could be represent a more expensive cost than realized depth diving. Indeed, this paradox is probably linked with contrasting thermoregulation processes. During daylight, a general hypothermia occurs and is believed to reduce energy expenditure. At sunrise occurs a re-warming to normothermia, contributing to increase heat-loss during the night. We hypothesise an energetic conflict between thermoregulation and digestive processes. During daylight, the organism may be unable to assimilate the end product of prey digestion (free fatty acids - FFA) inside the peripheral subcutaneous adipose tissues (SAT), because skin is no more blood perfused. During the night, re-warming and re-connecting to blood circulation peripheral tissues could be inevitable to end the assimilation of FFA inside the SAT.
Thus, we measured an increase of subcutaneous temperatures (used as a proxy of blood perfusion) in implanted penguins maintained in sea water tank in feeding condition (Lewden et al. 2017a) supporting this hypothesis. However, during fasting time in the same birds we also observed an increase of peripheral temperatures (Lewden et al. 2017b). Furthermore, the oxygen consumption rate of birds increased with fasting duration in water, while it was also higher when the flank tissue was warmer, indicating a thermoregulation cost due to greater perfusion. Fasting king penguins in water maintained peripheral perfusion probably to access subcutaneous fat stores. Hence, the observed normothermia in peripheral tissues of king penguins at sea, upon completion of a foraging bout, is likely explained by their nutritional needs: depositing FFA in subcutaneous tissues after profitable foraging (feeding condition) or mobilizing FFA to fuel metabolism, when foraging success was insufficient (fasting condition).
Cold acclimatization in Black-capped chickadees (Poecile atricapillus L.) (2009-2017)
During Canadian winter, chickadees have to cope with harsh condition with a decrease of daytime reducing their foraging time compared to an increase of fasting time during the night and the low temperature induced high heat lost. However, even if to maintain their ability to fly their small size (11g) prevent them to accumulate large fat reserve Black-capped chickadees are well adapted to assume a temperature gradient (body temperature-air temperature) higher than 40°C. Thus, independently to social rank, all individuals showed similar metabolic performance (Lewden et al. 2012) with an increase of pectoralis muscle mass explaining an increase of maximal thermogenic capacity (Msum; Petit, Lewden and Vézina 2014). Furthermore, chickadees expressed intra-seasonal metabolic flexibility (Petit, Lewden and Vézina 2013) but also hypothermic events during daytime (Lewden et al. 2014) in aim to adjust their energy expenditures during winter. Finally for this small passerine, the plumage represents an efficient insulating barrier to maintain high stable temperature (Lewden et al. 2017) characteristic to endotherms.
Biologist in Antarctica (2011-2013)
<h4>Research projects</h4> <p>Any research projects I'm currently working on will be listed below. Our list of all <a href="https://biologicalsciences.leeds.ac.uk/dir/research-projects">research projects</a> allows you to view and search the full list of projects in the faculty.</p>
French qualification - Section 66 and 68