Seasonal Adaptations in the Breathing Mechanics of High Arctic Ptarmigan.

Rock Ptarmigan (Lagopus mutus) inhabit the alpine regions of the northern hemisphere. A sub species of these birds found only on the high arctic islands of Svalbard, Norway seasonally deposit very large amounts of body fat. This fat serves as emergency stores of energy for the arctic winter when these birds repeatedly face potentially lethal periods of total starvation, due to extreme weather in combination with permanent darkness. In summer these birds normally weigh less then 0.5kg but during autumn their mass doubles to around 1kg, with body fat making up more than 30% of their body weight. This adaptation to life in high arctic conditions represents a significant physiological challenge for these animals, not only in providing the resources to deposit such a large amount of fat but also functioning with the relatively large extra body mass. The Codd lab has recently demonstrated that accessory breathing structures found on the ribs (uncinate processes) act as levers for the forward and downward movement of the ribs and sternum, respectively, when the bird is breathing in and also as a mechanical strut for muscles to pull the sternum up when the bird breathe out. Interestingly these structures vary in length depending if the bird is adapted to running, flying or diving. The rock ptarmigan have unique uncinate processes which suggest there may be fundamental differences in their mechanics of ventilation. Moreover, because during winter the additional mass is primarily deposited around the breast musculature and abdomen, respiratory movements may also be severely affected. We believe that L. m. hyperboreus will demonstrate respiratory adaptations that may the recruitment of novel accessory breathing muscles and pelvic aspiration to ventilate their lungs when their body mass is high. We will use electromyography to determine whether target muscles are active during ventilation or locomotion. Interclavicular and abdominal air sacs pressure will be recorded and locomotion will be monitored using video footage. For metabolic power we will use respirometry. The Department of Arctic Biology (University of Tromso) where experiments will take place is well set up for the maintenance of ptarmigan colonies under natural conditions; expertise and facilities which are not available in the UK. Examination of the breathing mechanics of ptarmigan will be fascinating and shed new light on the complexities of avian respiration. Our study will be the first to determine the effect of seasonal fluctuations in body mass to the mechanics of breathing in birds.

Unlike mammals, birds breathe not by contraction and relaxation of a muscular diaphragm but by the rhythmic pumping up and down of the sternum, which in turn facilitates the bellows-like movement of air through the air sac system to the lung, where gas exchange occurs. The avian lung is highly efficient and complex, with each breath taking an average of two cycles of inspiration and expiration to move through the respiratory system. In birds both inspiration and expiration are active processes driven by the hypaxial musculature; in conjunction with rib movements, the sternum is actively moved downwards during inspiration and pulled upwards during expiration. Recent work has demonstrated that acessory breathing structures, the uncinate processes, play a crucial role in both inspiration and expiration in birds. A sub species of Rock Ptarmigan, found only on the high arctic island of Svalbard, Norway, seasonally deposit large amounts of fat around the breast and abdominal regions which helps them to survive overwinter. These seasonal changes in weight represent a significant challenge for these birds as this increased mass must continually be moved up and down with each breath. Therefore, this project will examine adaptations in the respiratory mechanics of summer (low body mass) and winter (high body mass) Svalbard Rock Ptarmigan. I will use electromyography to determine whether target muscles are active during ventilation or locomotion. Interclavicular and abdominal air sacs will be cannulated with polyethylene tubing connected to miniaturised differential pressure transducers which will record changes in pressure. Locomotion will be monitored using video footage and accelerometry. Matching kinematic data with ventilation will enable the quantification of the degree of coupling. Metabolic power will be calculated using respirometry.