Phenotypic flexibility in body mass, basal metabolic rate and summit metabolism in southern red bishops (Euplectes orix): responses to short term thermal acclimation.

Avian basal metabolic rate (BMR) and summit metabolism (Msum) vary within individuals in response to seasonal acclimatization in free-ranging birds, and thermal acclimation under laboratory conditions. We examined relationships between acclimation air temperature (Tacc) and body mass (Mb), BMR and Msum in female southern red bishops (Euplectes orix) from a relatively mild coastal site and a seasonally colder, inland site. Following acclimation for 21days to Tacc=10, 22 or 35°C, Mb, BMR and Msum were all significantly and negatively related to Tacc. The significant relationship between BMR and Tacc did not remain after Mb was included as a covariate, whereas that between Msum and Tacc did. A subsequent reverse acclimation protocol, where bishops were acclimated to a second Tacc value and then re-acclimated to the first, revealed that short-term changes in Mb and BMR were completely reversible, but changes in Msum were only partially reversible. Following the reverse-acclimation protocol, metabolic expansibility (Msum/BMR) varied significantly with air temperature, being greatest at Tacc=35°C. Our data suggest that the intraspecific variation in seasonal metabolic variation previously reported for this species is at least partly driven by factors other than temperature.

van de Ven TM ，Mzilikazi N ，McKechnie AE 《-》

Phenotypic flexibility in the basal metabolic rate of laughing doves: responses to short-term thermal acclimation.

McKechnie AE ，Chetty K ，Lovegrove BG 《JOURNAL OF EXPERIMENTAL BIOLOGY》

Seasonal metabolic variation in two populations of an Afrotropical euplectid bird.

van de Ven TM ，Mzilikazi N ，McKechnie AE 《-》

Uncoupling Basal and Summit Metabolic Rates in White-Throated Sparrows: Digestive Demand Drives Maintenance Costs, but Changes in Muscle Mass Are Not Needed to Improve Thermogenic Capacity.

Barceló G ，Love OP ，Vézina F 《-》

Evidence for a maintenance cost for birds maintaining highly flexible basal, but not summit, metabolic rates.

Reversible phenotypic flexibility allows organisms to better match phenotypes to prevailing environmental conditions and may produce fitness benefits. Costs and constraints of phenotypic flexibility may limit the capacity for flexible responses but are not well understood nor documented. Costs could include expenses associated with maintaining the flexible system or with generating the flexible response. One potential cost of maintaining a flexible system is an energetic cost reflected in the basal metabolic rate (BMR), with elevated BMR in individuals with more flexible metabolic responses. We accessed data from thermal acclimation studies of birds where BMR and/or Msum (maximum cold-induced metabolic rate) were measured before and after acclimation, as a measure of metabolic flexibility, to test the hypothesis that flexibility in BMR (ΔBMR), Msum (ΔMsum), or metabolic scope (Msum - BMR; ΔScope) is positively correlated with BMR. When temperature treatments lasted at least three weeks, three of six species showed significant positive correlations between ΔBMR and BMR, one species showed a significant negative correlation, and two species showed no significant correlation. ΔMsum and BMR were not significantly correlated for any species and ΔScope and BMR were significantly positively correlated for only one species. These data suggest that support costs exist for maintaining high BMR flexibility for some bird species, but high flexibility in Msum or metabolic scope does not generally incur elevated maintenance costs.

Swanson DL ，Stager M ，Vézina F ，Liu JS ，McKechnie AE ，Amirkhiz RG ... -  《Scientific Reports》