Avian phenotypic transitions; acting constraints, mechanisms and consequences

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The long-term objectives of this program are to decipher the mechanisms that limit phenotypic flexibility in birds facing high energy demands and to determine the consequences of these limits on fitness. Over the next five years, we will focus on phenotypic transitions associated with wintering in cold climates, migration and reproduction. These life-history stages involve energy demands among the highest known in vertebrates and, in birds, are considered energy bottlenecks affecting body composition and physiological condition. More precisely, we will (1) determine the rate and amplitude of metabolic flexibility in response to rapid changes in ambient temperature and measure the physiological consequences of phenotypes mismatched to temperature variations This first project will be conducted at the UQAR avian facility by exposing three models species (black-capped chickadees, Poecile atricapillus, snow buntings, Plectrophenax nivalis, white throated sparrow, Zonotrichia albicollis) to two thermal gradients and by tracking individual changes in metabolic performance and physiological condition over time. We will also (2) examine how metabolic performance influences individual fitness. This will be done at the Macpès research forest where we work with free-living chickadees since 2009. Winter metabolic performance, individual flexibility, physiological condition and aging rate will be related to both survival and reproductive success. Using snow buntings as our model, we will also (3) determine the effects of phenotypic transitions on metabolic performance of these Arctic migrants and investigate how conflicting demands for breeding and thermoregulation in the High-Arctic (Alert, Nunavut) shape phenotypes during the transition from migration to breeding. This will involve repeated measurements in outdoor captive birds throughout winter as well as measures on free-living birds during premigratory fattening and during the period from their arrival on the breeding ground to the end of breeding. This program provides an integrated comprehension of the interplay between ecological and physiological constraints that shape adaptive phenotypic flexibility. On the long term, our research will shed light on the limits of avian phenotypic flexibility in contrasting conditions and will help identify natural constraints in which these limits may be reached.