Abstract
Reaction norms reflect an organisms' capacity to adjust its phenotype to the environment and allows for identifying trait values associated with physiological limits. However, reaction norms of physiological parameters are mostly unknown for endotherms living in natural conditions. Black-capped chickadees (Poecile atricapillus) increase their metabolic performance during winter acclimatization and are thus good model to measure reaction norms in the wild. We repeatedly measured basal (BMR) and summit (Msum) metabolism in chickadees to characterize, for the first time in a free-living endotherm, reaction norms of these parameters across the natural range of weather variation. BMR varied between individuals and was weakly and negatively related to minimal temperature. Msum varied with minimal temperature following a Z-shape curve, increasing linearly between 24°C and −10°C, and changed with absolute humidity following a U-shape relationship. These results suggest that thermal exchanges with the environment have minimal effects on maintenance costs, which may be individual-dependent, while thermogenic capacity is responding to body heat loss. Our results suggest also that BMR and Msum respond to different and likely independent constraints.
Highlights
Phenotypic flexibility is the ability of a fully-developed organism to rapidly and reversibly adjust its phenotype to track short-term environmental changes [1].PLOS ONE | DOI:10.1371/journal.pone.0113617 November 26, 2014Reaction Norms of Metabolic PerformanceBecause it allows for individuals to match their physiology with the requirements of their surroundings, phenotypic flexibility should improve survival and influence fitness [2,3].The capacity to adjust phenotypic traits to changes in the environment is studied through reaction norms, which describes the flexibility of a trait across an environmental gradient (Figure 1) [4,5,6]
Residual measured basal (BMR) and summit (Msum) did not differ between individuals (p50.1) and its reaction norm was consistent with scenario 3
Our goal was to investigate reaction norms of BMR and Msum through the natural range of weather variations experienced by a small endotherm
Summary
The capacity to adjust phenotypic traits to changes in the environment is studied through reaction norms, which describes the flexibility of a trait across an environmental gradient (Figure 1) [4,5,6]. According to Nussey et al 2007 [5], Brommer 2013 [3] and Mc Kechnie 2008 [6], reaction norms can be characterized by four parameters. The elevation is the mean trait expression (i.e. the intercept), the slope, which represents phenotypic flexibility, measures the change in trait value for a given change in an environmental parameter, the amplitude is the difference between minimal and maximal trait values and the shape (e.g. linear, sigmoid) informs on the limits of adjustment in a trait over a given range of change in the environment
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