Trade-offs In Energy Allocation Research Articles

Energetic cost of communication.

Communication signals may be energetically expensive or inexpensive to produce, depending on the function of the signal and the competitive nature of the communication system. Males of sexually selected species may produce high-energy advertisement signals, both to enhance detectability and to signal their size and body condition. Accordingly, the proportion of the energy budget allocated to signal production ranges from almost nothing for many signals to somewhere in excess of 50% for acoustic signals in short-lived sexually selected species. Recent data from gymnotiform electric fish reveal mechanisms that regulate energy allocated to sexual advertisement signals through dynamical remodeling of the excitable membranes in the electric organ. Further, males of the short-lived sexually selected species, Brachyhypopomus gauderio, trade off among different metabolic compartments, allocating energy to signal production while reducing energy used in other metabolic functions. Female B. gauderio, by contrast, do not trade off energy between signaling and other functions. To fuel energetically expensive signal production, we expect a continuum of strategies to be adopted by animals of different life history strategies. Future studies should explore the relation between life history and energy allocation trade-offs.

Substock variation in reproductive traits in North Sea cod (Gadus morhua)

The North Sea stock of Atlantic cod ( Gadus morhua ) is comprised of a number of subcomponents that differ both genetically and phenotypically. A potential cause for such spatial variability is adaptive divergence, which may be linked to differences in thermal environment and (or) historical fishing pressure. Here we present evidence that spatial variation in maturity–size relationships in the wild has a significant intrinsic component. Using a common-environment experiment on wild-caught juveniles raised through to maturity, we demonstrate that cod from the southern North Sea (SNS) mature at larger sizes than those from the northwestern North Sea (NWNS) despite broadly similar growth rates. Consistent with these experimental results, year-class-specific maturity ogives for recent maturing year classes (1999–2001) suggested that the length at which 50% of females reached maturity was 11 cm greater for SNS than for NWNS cod. Under a common environment, smaller female size at maturity partly reflected higher relative liver weight, with NWNS females having a higher relative liver weight than SNS females. By investigating maturation under controlled conditions, our study provides evidence for life history trade-offs in energy allocation between growth, energy storage, and reproduction that may underlie the spatial variation observed in the field.

Chemical bioactivity of sponges along an environmental gradient in a Mediterranean cave

SuMMarY: The bioactivity of the most abundant sponges from three communities in a Mediterranean cave was assessed by Microtox ® assay in two seasons, spring (June) and autumn (november). We quantified bioactivity as a proxy for the investment in production of biologically active substances, and we related sponge bioactivity to growth form, growth rates, and physical contacts of each species with other species. We established a threshold for classifying a species as bioactive based on a comparison between the results of the Microtox ® and the sea urchin embryo toxicity bioassay. a total of 30 spe cies were included in the study, of which 50% were bioactive in some community or season. Significant ecological (between communities) and seasonal variation in mean bioactivity was found. When sponge bioactivity was related to sponge growth shape, it was found that the encrusting species tended to be more toxic than the non-encrusting ones. There was a negative relationship between bioactivity and sponge growth, suggesting a trade-off in energy allocation to defence and to other biological functions. Furthermore, a negative correlation was found between bioactivity and positive associations with other species. These results highlight the important role of chemically-mediated interactions in cave communities.

Large litter size increases maternal energy intake but has no effect on UCP1 content and serum-leptin concentrations in lactating Brandt’s voles (Lasiopodomys brandtii)

Lactation is the most energetically demanding period in the female mammal's life. We measured maternal energy intake, uncoupling protein 1 (UCP1) content in brown adipose tissue (BAT), serum-leptin concentration, and litter growth in lactating Brandt's voles (Lasiopodomys brandtii) with different litter sizes. Litter mass was positively related to litter size but there was no difference in pup mass at birth. Maternal gross energy intake at peak lactation was positively correlated with litter size and litter mass. Maternal resting metabolic rate (RMR) was positively correlated with litter mass, but not with litter size. No significant differences were detected in body-fat mass, serum-leptin concentration, or UCP1 in lactating voles with different litter sizes. Serum-leptin concentration was negatively correlated with energy intake during lactation. Our data did not support the hypothesis that there is a trade-off in energy allocation between maternal maintenance and offspring growth in lactating Brandt's voles, but support the idea that if the mothers with ten pups should have less energy available for their maintenance than mothers raising fewer pups. Also, leptin is probably not the only factor that induces the high energy intake in mothers with large litter sizes, although it was involved in the regulation of energy intake during lactation.

Metabolic rate, behaviour and winter performance in juvenile Atlantic salmon

Summary 1Contrasting results of relations between standard metabolic rate, behaviour and performance suggest that the evolutionary trade-offs in energy allocation between metabolisms and other parts of the energy budget depend on environmental conditions. Here, we show how habitat complexity changes the relationship between standard metabolic rate, behaviour and performance (winter energy loss-rates) in juvenile Atlantic salmon (Salmo salar L.). 2Juvenile Salmon, individually screened for standard metabolic rate, were stocked in replicated semi-natural stream channels with and without sheltering possibilities under ledge cover. We recorded the use of ledged areas, energy-loss rates and feeding activity during a 61-day period. 3In the channels with ledge cover, individuals with relatively higher standard metabolic rates used areas outside of the cover more frequently and had higher feeding frequency than individuals with lower standard metabolic rates. No relationship was apparent between areas used, feeding and standard metabolic rate for the individuals within the no-cover treatments. In channels without cover, there was a negative relationship between standard metabolic rate and performance (energy balance), whereas standard metabolic rate did not affect performance in channels with ledge cover. 4The effect of standard metabolic rate on performance depended on habitat complexity expressed through differences in behaviour. In channels with ledge cover, individuals with higher standard metabolic rates were apparently able to compensate for higher metabolic costs by utilizing a riskier habitat outside the cover and attaining a higher feeding success. 5The present study demonstrates that the relationship between standard metabolic rate and performance may be dependent on habitat complexity and vary on small spatial scales, contributing to the persistence of large variation in standard metabolic rate within populations.

Contrasts in the capacity and underlying mechanisms for compensatory growth in two pelagic marine fishes

The widespread capacity for teleost fishes to engage in compensatory growth suggests there are costs or trade-offs that constrain normal growth to sub-maximal rates. Some potential trade- offs include behavioral conflicts between foraging and avoiding predators, and physiological aspects of energy allocation between synthesis of new tissue and functional demands of metabolism and maintenance. We examined the capacity for compensation and some potential underlying mecha- nisms in juveniles of 2 northern Pacific fish species, walleye pollock Theragra chalcogramma and sablefish Anoplopoma fimbria. Fish were deprived of food for 2 to 3 wk, then returned to ad libitum rations. Growth rates were subsequently compared to those for continually fed fish for up to 16 wk, and potential trade-offs in behavior (food consumption, routine swimming speeds, and response to a predator) and physiology (indexed by critical swimming speeds) were examined during 3 time peri- ods: immediately after deprivation, after 4 wk of ad libitum rations, and after 9 wk. We distinguished between routine swimming speeds, which indicate volitional motor activity, and critical swimming speeds, which estimate physiological capacity by forcing fish to swim to exhaustion against an increasing current. Previously deprived walleye pollock exhibited a clear, sustained capacity for accelerated growth, allowing them to quickly catch up in size to continually fed fish. Sablefish, how- ever, exhibited only a minor level of growth compensation. Underlying mechanisms of compensatory growth also differed between the 2 species. Previously deprived walleye pollock increased food con- sumption to levels 3 to 4× greater than those of control fish and reduced energy expenditure by low- ering routine swimming speeds. Compensating sablefish did not differ from control fish in consump- tion rates or routine swimming, but had lower critical swimming speeds than control fish, suggesting a trade-off in energy allocation. Responses to a simulated predator threat did not differ between pre- viously deprived and continually fed fish of either species. The experimental results are suggestive of different mechanisms, behaviorally based for walleye pollock and physiologically based for sablefish, associated with accelerated growth. The differences between the 2 species in integrated processes of growth, behavior, and physiology are likely to be a function of their contrasting life history strategies and different baseline growth rates.

Effect of brood size manipulation on offspring physiology: an experiment with passerine birds.

The environment experienced during ontogeny has a significant impact on the physiological condition of offspring. This, in turn, forecasts survival probabilities and future reproductive potential. Despite the prominent role that the concept of condition plays in evolutionary studies, the physiological and biochemical characters that define it remain relatively unexplored. In this study, we quantified the impact of brood size manipulations on the physiology and biochemistry of nestling tree swallows (Tachycineta bicolor) shortly before they fledged. Over two breeding seasons, we either increased or decreased the number of individuals in a brood by a single nestling. Every 2-4 days, we determined the resting rate of oxygen consumption [V(O(2))] of individuals in each brood. Growth was followed until 16 days of age, at which time, to look for potential trade-offs in energy allocation, we measured total lipid mass, skeletal muscle and organ mass, indices of blood oxygen-carrying capacity and the activities of key metabolic enzymes in various tissues. Surprisingly, there was a minimal response of most characters to brood manipulation, suggesting that physiological and biochemical development is relatively invariant except perhaps under extreme conditions. Individuals reared in artificially enlarged broods, however, had a significantly lower body mass, body-size-adjusted [V(O(2))], gizzard mass and total lipid mass. These individuals also had decreased activity of cardiac 3-hydroxyacyl CoA dehydrogenase, suggesting a decreased capacity for oxidation of fatty acids. How these characters affect survival or the future adult phenotype remains unknown.

Effects of dietary quality on basal metabolic rate and internal morphology of European starlings (Sturnus vulgaris).

European starlings (Sturnus vulgaris) were fed either a low- or high-quality diet to test the effects of dietary quality on basal metabolic rate (BMR) and internal morphology. Basal metabolic rate did not differ significantly between the two dietary groups, but internal morphology differed greatly. Starlings fed the low-quality diet had heavier gastrointestinal tracts, gizzards, and livers. Starlings fed the high-quality diet had heavier breast muscles. Starlings on the low-quality diet maintained mass, while starlings on the high-quality diet gained mass. Dry matter digestibility and energy digestibility were lower for starlings fed the low-quality diet, and their food and water intake were greater than starlings on the high-quality diet. The lack of dietary effect on BMR may be the result of increased energy expenditure of digestive organs paralleling a reduction of energy expenditure of organs and tissues not related to digestion (i.e., skeletal muscle). This trade-off in energy allocation among organs suggests a mechanism by which organisms may alter BMR in response to a change in seasonal variation in food availability.

The evolutionary context of chronic allergic conditions : The Hiwi of Venezuela.

The question of why populations with ecologies that resemble our evolutionary past rarely experience allergic conditions such as asthma has intrigued many biomedical scientists. Here we present descriptive data on the ecological context of allergic sensitization among the Hiwi of southwestern Venezuela and suggest reasons for why this and other lowland South American Indian groups do not express the allergic response at levels seen in industrialized contexts. Allergic sensitization among the Hiwi appears to be negligible. This absence occurs in the context of high exposure to macroparasites (mainly hookworm), nutritional stress, frequent and prolonged breastfeeding, low indoor allergen deposition, and few hours spent per day indoors. We conclude that seeking unidimensional answers to the question of why isolated human groups generally experience few allergic conditions is potentially flawed because allergies are produced by a multifaceted immunoglobulin E (IgE) system that responds in complex ways to the environmental and behavioral exposures we examined. Instead, we propose a general model of physiological trade-offs in energy allocation between production of IgE of undefined specificity and production of allergen-specific IgE. In addition, we consider the simultaneous effects that exposures such as nutritional stress, allergen exposure, and breastfeeding may have on these trade-offs.

Metabolic Aspects of the Trade-Off between Fecundity and Longevity in Drosophila melanogaster

An antagonistic pleiotropy between early fecundity and longevity has been well demonstrated in Drosophila melanogaster. It has been suggested that this pleiotropy may in part be due to a trade-off in energy allocation between reproduction and survival. We have tested this hypothesis by examining five populations of Drosophila melanogaster that show increased longevity following laboratory selection for postponed reproduction. These were compared to five control populations. We measured body mass, lipid and carbohydrate content, metabolic rate, and fecundity over the adult life span of the flies. Energy content brought forward into the adult stage from the pupae and adult metabolic rate were identicalfor short-and long-lived flies. Long-lived flies showed decreased fecundity and increased storage of lipid and carbohydrate compared to short-lived flies. Our study is the first to measure simultaneously allocations of metabolic energy resources between various forms of metabolic storage and reproduction in lines of Drosophila melanogaster and to measure their equivalence using a common energy unit (J). Energy equivalence analysis demonstrated that the trade-of in energy allocation between fecundity and metabolic storage was not quantitatively perfect with regard to energy values. Long-lived flies accumulated additional lipid and carbohydrate by forgoing early reproduction, but these accumulated metabolic resources were far lower in energy content than were the additional eggs produced by short-lived flies.

METABOLIC AND DIGESTIVE RESPONSES TO ARTIFICIAL SELECTION IN CHICKENS.

Compared to ancestral wild jungle fowl, domestic broiler chickens have been consciously selected for large body size, relatively large pectoral muscles, rapid growth, and high feed efficiency. Hence intraspecific comparisons of these two strains could help identify consequences of unconscious artificial selection, trade-offs in energy allocation, and factors limiting energy budgets. We therefore compared our measurements of many corresponding parameters in both strains: growth rate, energy intake, digestive efficiency, metabolic rate and its components, organ masses, and intestinal brush-border nutrient transporter and hydrolase activities and capacities, as functions of age and body mass in zero- to nine-week-old chicks. Both strains prove to have the same digestive efficiency. Compared to equal-sized jungle fowl, broilers have higher daily energy intake and activity costs. Broilers have relatively longer and wider, hence heavier, small intestines, and their other gut compartments are also relatively larger. Offsetting these increases, broilers have relatively smaller brains and leg bones, these being much less important to a captive bird than to a wild bird exposed to predators. Broilers have generally lower intestinal transporter activities, but relatively higher transporter capacities because of their larger guts. Among domestic chicken strains, comparison of broilers with layers, the former having been consciously selected for much higher growth rates, yields generally similar conclusions. Thus, as recognized in broad outline by Darwin, domestication provides clear examples of conscious selection, of unconscious selection for traits prerequisite to the consciously selected traits, and of unconscious selection against traits rendered less important or competing for space or energy.

Trade-offs in Energy Allocation During Lactation

SYNOPSIS. During lactation, mothers require energy to meet both maternal and offspring requirements. If a mother exports too much energy to dependent offspring (in milk), her weight loss may be excessive and maternal risk may increase. Conversely, too little energy allocation to offspring may reduce the growth rate or induce mortality of dependent offspring. This paradigm was evaluated in cotton rats ( Sigmodon hispidus ) supporting small (3 pup) and large (6 pup) litters from early to late lactation. Several types of evidence indicate that physiological constraints limit the ability of mothers with large litters to provide resources to offspring. Mothers with large litters produced a dilute, energy-poor milk and their rates of food intake, weight loss and energy export per litter appeared to approach physiological maxima. Whereas the energy exported to pups in small litters increased from early to late lactation, the energy flow per pup in large litters was consistently low; consequently, offspring in large litters had low growth rates. An increase in either maternal food intake or weight loss (catabolism of maternal tissue) could have provided additional energy to offset the low growth rate of pups in large litters. However, mothers with large litters did not substantially increase their food intake or weight loss compared with mothers supporting small litters. These results indicate that the maternal support of offspring in large litters is limited. The pattern of energy allocation shown by cotton rats with large litters likely reflects a compromise between meeting maternal and offspring energy requirements ( cf. , Parker and Macnair, 1979). The energy flow is greater than optimal for the parent but less than optimal for the offspring. Less maternal-offspring conflict occurs in small than large litters because offspring in small litters maintain a high growth rate at a relatively low maternal cost. Yet, under favorable environmental conditions, the reduction in maternal-offspring conflict has no apparent fitness benefit.

Some costs of reproduction for male bushcrickets, Requena verticalis (Orthoptera : Tettigoniidae) allocating resources to mate attraction and nuptial feeding

The cost of reproductive effort is known to result in a trade-off between current and future reproduction. Similarly, trade-offs in energy allocation may occur between components of reproductive effort, mating and parental effort, within a single reproductive episode. We investigated the energy allocated to mating effort (calling to attract females) and parental effort (donation of spermatophore nutrients at mating) by male bushcrickets, Requena verticalis, under two dietary regimes. Males provided with a low quality diet reduced the daily energy allocated to calling activity while maintaining their investment in spermatophores. Males provided with a high quality diet did not allocate more resources per day to their spermatophores but stored excess energy for future reproduction. Thus, on a per day basis, males appear to hold constant their investment in the spermatophore at the cost of reduced mating effort when resources are limited. Males on both diets, however, increased the size of their spermatophore donations when the interval between female encounters was increased. One explanation for this pattern could be a frequency-dependent optimization of spermatophore size.

Cost of reproduction in Douglas-fir

The balance between allocating energy resources to reproduction or growth has considerable theoretical interest. Conflicting ecological requirements and evolutionary pressures often necessitate a trade-off in energy allocation. We obtained measurements on seed-cone production and annual ring width of 365 Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees from 29 open-pollinated families for 8 years. Phenotypic, genetic, and environmental correlations were computed for seed-cone production and ring width for each year. Five of the eight environmental correlations were negative (range −0.077 to −0.305), reflecting the reality of the trade-off in physiological terms. Six of the eight genetic correlations were negative (range −0.199 to −0.776), indicating that a trade-off exists at the genetic level between energy allocation to reproduction and to somatic growth. These findings agree with the current theory of life-history evolution. Key words: Pseudotsuga menziesii, cone production, annual ring width, genetic correlation.

Inter- and intraspecific patterns of reproductive effort in four species of cone shells (Conus spp.)

Patterns of reproductive effort were examined both within and between 4 species of the tropical marine gastropod genus Conus from Hawaii in 1979. Caloric content was measured for the somatic tissues of female cone shells and for their egg capsule masses. These data were used to calculate (1) current reproductive effort, which was the ratio of annual energy produced as spawn to the sum of the annual energy produced as spawn plus the annual energy produced as somatic tissue; and (2) weight-specific reproductive effort, which was the ratio of annual energy produced as spawn to the total energy content of the female body just before spawning. For C. pennaceus, during the approximately 10 yr of life of a female, current reproductive effort rose from about 0.35 at 2 yr to about 0.85 at 10 yr. In contrast, weight-specific reproductive effort remained relatively constant throughout life for C. pennaceus (about 0.2 to 0.5), C. abbreviatus (about 0.2 to 0.3), C. flavidus (about 0.2 to 0.3) and C. quercinus (about 0.1 to 0.2). It is suggested that weight-specific reproductive effort may be useful as an index of the selective importance of the survival cost of present reproduction, while current reproductive effort more closely reflects the selective importance of energy allocation tradeoffs. Data on the 4 species of Conus examined support the hypothesis that reproductive effort should be positively correlated with extrinsic adult mortality and negatively correlated with the variability of juvenile survivorship. The data also suggest a possible relationship between reproductive effort and the cost of parental care.