Cold- and exercise-induced peak metabolic rates in tropical birds

Abstract

Compared with temperate birds, tropical birds have low reproductive rates, slow development as nestlings, and long lifespans. These ''slow'' life history traits are thought to be associated with reduced energy expenditure, or a slow ''pace of life.'' To test predictions from this hypothesis, we measured exercise-induced peak metabolic rates (PMRE) in 45 species of tropical lowland forest birds and compared these data with PMRE for three temperate species. We also compared cold-induced PMR (PMRC) with PMRE in the same individuals of 19 tropical species. Tropical birds had a 39% lower PMRE than did the temperate species. In tropical birds, PMRC and PMRE scaled similarly with body mass (Mb), but PMRE was 47% higher than PMRC. PMRE averaged 6.44 ؋ basal metabolic rate (BMR) and PMRC averaged 4.52 ؋ BMR. The slope of the equation relating PMRE to Mb exceeded the slope for the equation for BMR vs. Mb, whereas slopes for the equations of PMRC and BMR vs. Mb did not differ. Mb-adjusted residuals of PMRE were positively correlated with residual BMR, whereas residual PMRC and residual BMR were not correlated. PMRE and PMRC were not correlated after we corrected for Mb. Temperate birds maintained their body temperature at an 8.6°C lower average air temperature than did tropical species. The lower PMRE values in tropical species suggest that their suite of life history traits on the slow end of the life history continuum are associated with reduced metabolic rates. maximum metabolic rate ͉ summit metabolism ͉ metabolic scope ͉ pace of life ͉ cold tolerance E cological physiologists have devoted considerable effort to examining the upper limits of physiological performance, especially locomotor performance and metabolic power production during cold exposure. An implicit or explicit hypothesis in this work is that individual variation in performance is correlated with fitness: higher performance such as faster running or greater metabolic power output leads to increased survival and/or reproductive success. In the past few decades, a variety of performance indices have been measured in numerous species, and analyses have examined performance in mechanistic, phylogenetic, ecological, and evolutionary contexts.

Global patterns of seasonal acclimatization in avian resting metabolic rates

“…Msum is generally lower in species from warmer tropical and subtropical environments compared to colder, temperate environments (Swanson and Garland 2009;Wiersma et al 2007a). Our finding that winter residual Msum is significantly higher among temperate-zone species compared to tropical/subtropical species is consistent with this overall picture, as is the corresponding difference in W/S ratios.…”

Linkages between the life-history evolution of tropical and temperate birds and the resistance of their cells to oxidative and non-oxidative chemical injury

“…Tropical birds have a significantly lower basal and peak metabolic rate than temperate birds (Wiersma et al, 2007a;Wiersma et al, 2007b), which may translate into a higher production of damaging free radicals, because ROS production is highest when respiration rate is low. However, because tropical birds have high rates of survival (Ricklefs, 1997;Tieleman et al, 2006), they may have evolved efficient cellular mechanisms to regulate ROS-induced damage.…”

“…Evidence of a linkage between slow pace of life and low rate of metabolism in tropical birds came to light when it was shown that they had a significantly lower wholeanimal basal metabolic rate (Wiersma et al, 2007a) and peak metabolic rate as measured by cold-exposure or by exercise (Wiersma et al, 2007b). Later it was discovered that a contributing factor to the reduced rate of metabolism in tropical birds was their smaller metabolically active organs, such as the heart, liver, kidneys and pectoral muscles, compared with similar-sized temperate species (Wiersma et al, 2012).…”

A ‘slow pace of life’ in Australian old-endemic passerine birds is not accompanied by low basal metabolic rates

“…Given that tropical birds have smaller clutches, longer parental care, and higher juvenile and adult survival than their north-temperate counterparts [Moreau 1944;Skutch 1985;Martin 1996;Cardillo 2002;Russell et al 2004)], these studies support the notion that a slow 'pace of life' engenders a slow 'pace' of energy metabolism (e.g., Pearl 1928). However, it is unclear if low BMR in the tropics is a functional necessity or a byproduct of 'slow' life history, or instead is simply an outcome of living in warm, stable habitats with low requirements for thermoregulation, migration, or other energetically demanding activities (Wiersma et al 2007a). One way to resolve this is to examine the metabolic rates of temperate-breeding birds sharing the same 'slow' life-history traits as tropical passerines, and compare them with sympatric passerines with 'fast' life-histories.…”

“…Adults from a sedentary tropical population had lower metabolic rates than birds from a migratory north-temperate population. Similarly, two extensive comparative analyses showed that birds from Neotropical forests in Panama and Peru have lower BMR (Wiersma et al 2007b;Londoño et al 2015) and, in the Panamanian birds, lower maximal metabolic rates than species from temperate latitudes (Wiersma et al 2007a). Given that tropical birds have smaller clutches, longer parental care, and higher juvenile and adult survival than their north-temperate counterparts [Moreau 1944;Skutch 1985;Martin 1996;Cardillo 2002;Russell et al 2004)], these studies support the notion that a slow 'pace of life' engenders a slow 'pace' of energy metabolism (e.g., Pearl 1928).…”