Energetic Cost Of Growth Research Articles

Endocrine disruption from plastic pollution and warming interact to increase the energetic cost of growth in a fish.

Energetic cost of growth determines how much food-derived energy is needed to produce a given amount of new biomass and thereby influences energy transduction between trophic levels. Growth and development are regulated by hormones and are therefore sensitive to changes in temperature and environmental endocrine disruption. Here, we show that the endocrine disruptor bisphenol A (BPA) at an environmentally relevant concentration (10 µgl-1) decreased fish (Danio rerio) size at 30°C water temperature. Under the same conditions, it significantly increased metabolic rates and the energetic cost of growth across development. By contrast, BPA decreased the cost of growth at cooler temperatures (24°C). BPA-mediated changes in cost of growth were not associated with mitochondrial efficiency (P/O ratios (i.e. adenosine diphosphate (ADP) used/oxygen consumed) and respiratory control ratios) although BPA did increase mitochondrial proton leak. In females, BPA decreased age at maturity at 24°C but increased it at 30°C, and it decreased the gonadosomatic index suggesting reduced investment into reproduction. Our data reveal a potentially serious emerging problem: increasing water temperatures resulting from climate warming together with endocrine disruption from plastic pollution can impact animal growth efficiency, and hence the dynamics and resilience of animal populations and the services these provide.

Estimating the cost of growth in southern right whales from drone photogrammetry data and long-term sighting histories

Animal body size and growth patterns play important roles in shaping the life history of species. Baleen whales include the largest animals on the planet, with somatic growth costs expected to be substantial. We used unmanned aerial vehicle photogrammetry and long-term individual sighting histories from photo identification (1991-2019) to estimate the cost of somatic growth for southern right whales (SRWs) Eubalaena australis. A Richards length-at-age growth model was developed, based on 161 calves, 20 yearlings, 1 juvenile and 23 adults, ranging in age from newborn to 27 yr. Predicted lengths were 4.7 m at birth, 12.5 m at minimum age of first parturition (6 yr) and an asymptotic length of 14.3 m. A volume-at-age curve was estimated from the body volume versus length relationship, and converted to a mass-at-age curve, using data on body tissue composition of North Pacific right whales E. japonica (n = 13). The energetic cost of growth was estimated using published estimates of tissue lipid and protein concentrations. The cost of growth for SRWs (in MJ d-1) was 2112 at birth, 544 at 4 mo, 314 at 1 yr (~weaning age), 108 at 5 yr (minimum age of sexual maturity), 51.5 at 10 yr and 5.2 at 30 yr. The cumulative cost to age 30 was 764.3 GJ, but varied widely (458-995 GJ) depending on the tissue energy content. Our estimates represent a healthy SRW population, and provide a baseline to investigate individual and population level impacts of anthropogenic disturbance (including climate change).

Cortisol affects feed utilization, digestion and performance in juvenile rainbow trout (Oncorhynchus mykiss)

To quantify bioenergetic consequences of chronically or acutely elevated plasma cortisol levels, growth rates, feed conversion ratios and digestive performance was investigated in juvenile rainbow trout (Oncorhynchus mykiss) reared at 15 °C. Plasma cortisol levels were elevated using coconut oil based implants. A sham group received coconut oil without cortisol, (S), while a low (LC) and high (HC) cortisol group received implants containing 30 or 60 μg cortisol g−1 fish. An additional group of fish was reared under moderate thermal stress (22 °C, TS), while acute increases in plasma cortisol were achieved by subjecting fish to a daily stressor by chasing (DS). An undisturbed treatment group, reared at 15 °C served as control (C). Although feed intake was not affected by treatments, cortisol treated fish showed reduced growth rate and feed conversion efficiency compared to all other treatments. This was caused, in part, by impaired digestibility of protein, lipids and nitrogen free extract in the HC treatment, leading to a decrease in available metabolizable energy. The observed decrease in lipid digestibility did not appear to be caused by a reduced digestive lipase activity in the pyloric caeca and anterior intestine as this was not significantly different between treatments 90 min after feeding. Chronically elevated cortisol levels led to atrophy of the digestive system revealed by a loss in tissue mass of the intestine and pyloric caeca in the high cortisol treatment, as well as an overall decrease in viscerosomatic index. In addition, the energetic cost of growth was higher in both cortisol treated groups compared to all other treatments. The chronic temperature elevation resulted in improved lipid digestion compared to the control treatment, while growth performance was impaired, however apparently not correlated with elevated plasma cortisol levels. A moderate random daily stress event did not result in any changes of the studied parameters. The results obtained suggest both an atrophic effect of chronically elevated plasma cortisol levels on digestive tissues resulting in impaired nutrient assimilation, less available metabolizable energy, and an increased routine energy expenditure, leading to a higher cost of growth.

Increasing energetic cost of biosynthesis during growth makes refeeding deleterious.

Diet restriction (DR) enhances animals' health maintenance, but refeeding reverses its beneficial effects. However, to what degree refeeding reverses the beneficial effects of DR remains controversial. Here, I develop a theoretical model for reconciling the results of refeeding studies and understanding the dynamic and reversible mechanism underlying the effects of diet on health from the energetic viewpoint. By illustrating the negative correlation between health maintenance and the energetic cost of growth in animals under different diet regimes, the model explains why, in some cases, refed animals have better health and live longer than freely fed controls. More importantly, the model reveals that, in some species, the energetic cost of synthesizing biomass increases during growth, so the expensive compensatory growth induced by refeeding later in life offsets the benefits of the inexpensive retarded growth induced by diet restriction early in life. Thus, in these species, refeeding drives animals to allocate more energy to growth and less to maintenance and therefore leads to poor health status and shorter life span compared to freely fed controls.

The energetic and survival costs of growth in free-ranging chipmunks

The growth/survival trade-off is a fundamental aspect of life-history evolution that is often explained by the direct energetic requirement for growth that cannot be allocated into maintenance. However, there is currently no empirical consensus on whether fast-growing individuals have higher resting metabolic rates at thermoneutrality (RMRt) than slow growers. Moreover, the link between growth rate and daily energy expenditure (DEE) has never been tested in a wild endotherm. We assessed the energetic and survival costs of growth in juvenile eastern chipmunks (Tamias striatus) during a year of low food abundance by quantifying post-emergent growth rate (n = 88), RMRt (n = 66), DEE (n = 20), and overwinter survival. Both RMRt and DEE were significantly and positively related to growth rate. The effect size was stronger for DEE than RMRt, suggesting that the energy cost of growth in wild animals is more likely to be related to the maintenance of a higher foraging rate (included in DEE) than to tissue accretion (included in RMRt). Fast growers were significantly less likely to survive the following winter compared to slow growers. Juveniles with high or low RMRt were less likely to survive winter than juveniles with intermediate RMRt. In contrast, DEE was unrelated to survival. In addition, botfly parasitism simultaneously decreased growth rate and survival, suggesting that the energetic budget of juveniles was restricted by the simultaneous costs of growth and parasitism. Although the biology of the species (seed-storing hibernator) and the context of our study (constraining environmental conditions) were ideally combined to reveal a direct relationship between current use of energy and future availability, it remains unclear whether the energetic cost of growth was directly responsible for reduced survival.

Growth of the chicken embryo: Implications of egg size

Among avian species with large differences in egg size, changes in eggshell conductance and incubation time permit the water loss necessary for embryonic development. To what extent this happens for different-size eggs within a species is much less known. Chicken eggs with fresh egg weight (Wegg) either large (L,∼66g) or small (S,∼51g) were incubated at 38°C and 60% humidity; their yolk and albumen scaled almost in proportion to Wegg. Eggshell gas conductance scaled to 0.77 of Wegg, as it occurs inter-specifically, while external pipping and hatching occurred at similar times in S and L. Hence, L lost less water during incubation than S, and embryos of L were over-hydrated and those of S were dehydrated. The absolute values of embryo's weight, growth rate, oxygen consumption and the weight of the chorioallantoic membrane were similar between S and L during the first half of incubation, and greater in L in the second half. Incubation in hypoxia reduced growth rate in both sets and maintained the difference in growth trajectories between S and L. The energetic cost of growth and tissue maintenance did not differ significantly. It is concluded that,10+9 among chicken eggs of different sizes, 1) the growth rate of the embryo relates to the size of its egg, probably genetically and because of differences in water content, 2) eggshell conductance contributes, but incubation time does not, to the requirements for water loss. Therefore, the egg water balance during incubation may be the physiological constraint that limits the maximal variability in egg size compatible with embryonic survival.

Peaked Temporal Pattern of Embryonic Metabolism in an Emydid Turtle (Chrysemys picta picta)

Temporal patterns of embryonic metabolism integrate ontogenetic changes in the energetic costs of growth and maintenance. Unlike most other chelonians, which show a peaked pattern of embryonic metabolic rate (MR) over time, turtles of the family Emydidae have been depicted with unimodally increasing patterns. We incubated eggs of the emydid Chrysemys picta picta under standard conditions at 30°C and serially measured rates of oxygen consumption. Five eggs showed clear decreases in MR before hatching; two others that hatched during MR measurements showed increases in MR associated with muscular activity. MRs of hatchling turtles were lower than those of prehatching embryos for at least 60 days, suggesting persistent costs of biosynthesis in yolk-dependent late-stage embryos and early hatchlings.