Metabolic enzymes in seasonally acclimatized and cold acclimated rufous-collared sparrow inhabiting a Chilean Mediterranean environment

Abstract

Due to the higher energy requirements of birds during winter, it is predicted that the activities of metabolic enzymes (e.g., citrate synthase, CS and cytochrome C oxidase, COX) should increase in tandem with increases in rates of energy expenditure (e.g., basal metabolic rate, BMR). However, there is mixed support for the hypothesis of enzymatic acclimatization. Furthermore, there is little information about the effect of ambient temperature on energetics and tissue enzyme activity levels in passerines inhabiting seasonal Mediterranean environments. In this study we evaluated the interplay between BMR and enzyme activities of freshly caught individuals of the passerine Zonotrichia capensis in winter and summer in a Mediterranean environment from central Chile, and also in warm (30°C) and cold (15°C) lab-acclimated birds. The results revealed a lack of seasonal variation in BMR, thermal conductance and in the activity of CS and COX. However, we found higher BMR and lower thermal conductance in cold-acclimated than in warm-acclimated birds. Also, total CS activity was higher in the flight muscles of cold-acclimated than in warm-acclimated birds. We found also a significant correlation between BMR and total CS activity in pectoral muscle. Although some authors have suggested that BMR mainly depends on the metabolic intensity and mass of internal organs, our results revealed that skeletal muscles such as the flight muscles may also affect BMR. Finally, differences in the acclimation and acclimatization responses in Rufous-collared sparrows suggest that large-scale oscillations in the physical environment might maintain the capacity for flexibility in thermogenic traits through generations.

Energetic Effects of Pre-hatch Albumen Removal on Embryonic Development and Early Ontogeny in Gallus gallus

“…A reduction in the muscle function could have many effects, taking into consideration that in birds these tissues are responsible for locomotion and thermoregulation. In line with our results, other studies relating to birds suggest that muscles are an important source of heat in terms of shivering thermogenesis in seasonally acclimatized and cold acclimated birds (Liu et al, 2008; Zheng et al, 2008; Liknes and Swanson, 2011a,b; Swanson and Merkord, 2013; Peña-Villalobos et al, 2014). Therefore, a reduction of this enzymatic activity could have negative consequences in the early development of thermogenic capacity, and therefore survival in wild birds.…”

“…Indeed, some studies have found significant correlations between metabolic rates and metabolic enzyme activities. For instance, Zheng et al (2013) reported that basal metabolic rates and liver and muscle mitochondrial COX activities were positively correlated in Pycnonotus sinensis , and Peña-Villalobos et al (2014) observed a positive correlation between basal metabolic rates and pectoral CS activity in Zonotrichia capensis . In fact, we found that experimentally treated embryos in E20 presented lower enzymatic activities in the skeletal muscles, revealing that oxidative capacity is not a fixed trait throughout development.…”

“…Organs (liver, intestine, heart, and gizzard), CAM and yolk sac were removed and weighed (±0.0001 g). Animals were dissected on ice and the liver, pectoralis, and supracoracoideus were extracted, along with the major muscles of both lower limbs (iliotibialis cranialis, iliotibialis lateralis, iliofibularis, femorotibialis externus, fibularis longus, tibialis cranialis, extensor digitorum longus, and gastrocnemius complex) (Liknes and Swanson, 2011a; Peña-Villalobos et al, 2014). For the analyses we used the homogenates of the entire flight muscles (pectoralis plus supracoracoideus = pectoral muscles), the set of muscles of the lower extremities (leg muscles) and the liver.…”

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

“…The lack of temperature effect on the mass of the pectoral muscles was a surprising result given the measured increase in whole-body M sum in cold-acclimated birds. Other cases of un-altered skeletal muscles after exposure to cold have been reported (e.g., Williams and Tieleman 2000;Tieleman et al 2003;Peña-Villalobos et al 2014), but these studies used relatively mild temperatures as their cold treatment (e.g., 157C) and did not include M sum measurements. Nonetheless, similar to our study, American goldfinches (Spinus tristis) showed an increase in M sum (Dawson and Carey 1976) with no associated changes in pectoral muscles (Carey et al 1978), and captive dark-eyed juncos (Junco hyemalis) developed a larger heart and increased their M sum in response to cold without a change in the size of their pectoral muscles (Swanson et al 2014c).…”

Seasonal Metabolic Acclimatization Varies in Direction and Magnitude among Populations of an Afrotropical Passerine Bird

“…The physiological mechanisms driving phenotypic flexibility in M sum include adjustments in the mass of the pectoralis muscles and changes in the transport capacities for O 2 and metabolic substrates, whereas seasonal adjustments in BMR reflect changes in organ masses, mass-independent metabolic intensities of spe-cific organs, and the activity levels of metabolic enzymes (Swanson 2010;Peña-Villalobos et al 2014;Petit and Vézina 2014;Zhang et al 2015). Recent studies suggest that the functional link between BMR and M sum is not as clear as one might expect, an idea that is supported by the difference in physiological mechanisms determining flexibility in these variables (Swanson et al 2012;Petit et al 2013;Petit and Vézina 2014).…”