Rate Of Energy Acquisition Research Articles

Consequences of intraspecific competition for floral resources in heterogeneous landscapes for eusocial bees

Agricultural intensification is widely recognised as a primary driver of pollinator loss, but the success of land-management actions designed to remediate its impact is often mixed. Payments to farmers to increase habitat connectivity or the availability of floral and nesting resources may only result in short-term gains or even unintended consequences. The reasons may lie in changes to interaction networks or competition intensity that remain poorly understood. Models of pollination service typically implicitly assume pollinator population dynamics are regulated by nest-site availability, even though empirical evidence suggests nest-site occupancy is likely at least in part dependent on floral resource availability. To investigate the consequences of competition for floral resources in coarse-grained agricultural landscapes we extended an established model for bees combining optimal foraging and population dynamics, to include new functions for floral resource depletion and realistic colony dynamics. We find that intra-specific competition occurs late in the season forcing bees to forage underutilised sites situated further towards their foraging range limits. A lower rate of energy acquisition ultimately limits the size of the colony peak and delays its timing. Consequently, competition for floral resources can limit population size and distribution while at the same time contributing to a more stable and efficacious pollination service. Although competition was not found to be important in nest-site establishment success, the effect of a hunger gap early in the season on nest-site occupancy indirectly influences competition later in the season leading to complex outcomes.

Environment-dependent metabolic investments in the mixotrophic chrysophyte Ochromonas.

Mixotrophic protists combine photosynthesis and phagotrophy to obtain energy and nutrients. Because mixotrophs can act as either primary producers or consumers, they have a complex role in marine food webs and biogeochemical cycles. Many mixotrophs are also phenotypically plastic and can adjust their metabolic investments in response to resource availability. Thus, a single species's ecological role may vary with environmental conditions. Here, we quantified how light and food availability impacted the growth rates, energy acquisition rates, and metabolic investment strategies of eight strains of the mixotrophic chrysophyte, Ochromonas. All eight Ochromonas strains photoacclimated by decreasing chlorophyll content as light intensity increased. Some strains were obligate phototrophs that required light for growth, while other strains showed stronger metabolic responses to prey availability. When prey availability was high, all eight strains exhibited accelerated growth rates and decreased their investments in both photosynthesis and phagotrophy. Photosynthesis and phagotrophy generally produced additive benefits: In low-prey environments, Ochromonas growth rates increased to maximum, light-saturated rates with increasing light but increased further with the addition of abundant bacterial prey. The additive benefits observed between photosynthesis and phagotrophy in Ochromonas suggest that the two metabolic modes provide nonsubstitutable resources, which may explain why a tradeoff between phagotrophic and phototrophic investments emerged in some but not all strains.

Luck and tactics in foraging success: the case of the imperial shag

It has been proposed that predators searching for prey acquire food according to a probabilistic framework, where success is based on ‘luck’ and the odds of success vary with prey abundance. If true, this has major ramifications for variation in the rates of energy acquisition within animal populations, which is particularly pertinent in offspring provisioning and breeding success, because smaller animals (the young) cannot starve for as long as the adults. However, despite much general speculation about rates of food acquisition, no study has measured whether food encounter is probabilistic in wild animals. We used animal-mounted cameras to document all prey captures by wild imperial shagsLeucocarbo atricepsas they hunted underwater and show that, although they mostly do not have inter-prey acquisition time distributions that accord with a ‘luck-based’ framework assuming a constant probability of finding prey over time, there is no difference in the predicted amount of food captured between models that use the empirical data or theoretical Poisson-based fits of the data. We also noted considerable inter-individual differences in foraging success that far exceeded any differences between empirical and theoretical inter-prey acquisition time distributions. The data were used in a probabilistic foraging model that made explicit the mechanistic link between random prey encounters and food-dependent breeding success, indicating that ‘less lucky’ individuals could not provision their broods at rates commensurate with normal growth while the ‘lucky’ birds could do so easily. Given the nature of food encounter in these birds, coupled with substantial inter-individual variation in foraging success, we suggest that more successful individuals are particularly choosey about when, how and where to forage, which results in them operating with higher odds of success.

The metabolic response of the Bradypus sloth to temperature.

Poikilotherms and homeotherms have different, well-defined metabolic responses to ambient temperature (Ta), but both groups have high power costs at high temperatures. Sloths (Bradypus) are critically limited by rates of energy acquisition and it has previously been suggested that their unusual departure from homeothermy mitigates the associated costs. No studies, however, have examined how sloth body temperature and metabolic rate vary with Ta. Here we measured the oxygen consumption (VO2) of eight brown-throated sloths (B. variegatus) at variable Ta’s and found that VO2 indeed varied in an unusual manner with what appeared to be a reversal of the standard homeotherm pattern. Sloth VO2 increased with Ta, peaking in a metabolic plateau (nominal ‘thermally-active zone’ (TAZ)) before decreasing again at higher Ta values. We suggest that this pattern enables sloths to minimise energy expenditure over a wide range of conditions, which is likely to be crucial for survival in an animal that operates under severe energetic constraints. To our knowledge, this is the first evidence of a mammal provisionally invoking metabolic depression in response to increasing Ta’s, without entering into a state of torpor, aestivation or hibernation.

Effects of swim-with-dolphin tourism on the behaviour of a threatened species, the Burrunan dolphin Tursiops australis

Burrunan dolphins Tursiops australis are frequently targeted by tourism operations in Port Phillip Bay, Australia. This study aimed to provide first insights into whether swim-with-dolphin (SWD) vessels in Port Phillip Bay affect the behaviour of Burrunan dolphins via the use of Markov chain models. The presence of SWD vessels affected dolphins' travelling, foraging, milling and socialising behaviours. The time dolphins spent foraging in the presence of SWD vessels was significantly reduced, with average foraging bout length decreasing by 13.6%, foraging recovery time increasing by 47.6%, and the probability of transitioning from foraging to milling increasing 4-fold. Conversely, dolphins spent significantly more time milling and socialising in the presence of SWD vessels. The reduction in time spent foraging when SWD vessels are present could lead to a decrease in dolphins' rate of energy acquisition, whilst the increase in milling could increase their energy expenditure. Collectively, this may lead to reduced biological fitness with population level consequences. However, although the short-term behavioural budget of the dolphin population was significantly affected, SWD vessels did not significantly affect the cumulative (i.e. yearly) behavioural budget of Burrunan dolphins. Thus, the assumption that boat-based cetacean tourism has major negative effects on targeted populations may be flawed in some cases.

Low concentrations of large inedible particles reduce feeding rates of echinoderm larvae

The planktonic larvae of many marine invertebrates must feed to develop to metamorphosis. The rate at which feeding larvae accumulate energy affects the amount of time they must spend in the plankton, which affects larval dispersal and mortality; it may also affect the amount of energy gained before metamorphosis, and thus limit growth or survivorship of early juveniles. Rates of energy acquisition are partly determined by the quantity of edible particles in the plankton. However, the plankton also contains many particles that are too large to be ingested. Prior studies suggest that high concentrations of such large inedible particles reduce larval feeding rates. This study examines whether the feeding rates of larvae of southern California echinoderms are reduced by lower, more frequently encountered concentrations of large inedible particles. Larvae of a holothuroid, two asteroids, and three echinoids were fed 6-µm beads alone or with large inedible beads at 25–500 inedible beads mL−1. Five of the six species showed reduced clearance rates on 6-µm beads when exposed to as few as 25 inedible beads mL−1. In similar experiments on an asteroid and an echinoid using natural large inedible particles (centric diatoms), larval clearance rates were reduced at 25 cells mL−1 and higher. Larval clearance rates were reduced by ~50% in treatments of 100 or 500 large inedible particles mL−1. These results suggest that in nature, rates of food acquisition by larvae may depend not only on the abundance of food particles, but also on the abundance of potentially interfering non-food particles.

Is Maximum Food Intake in Endotherms Constrained by Net or Factorial Aerobic Scope? Lessons from the Leaf-Eared Mouse.

Food availability varies substantially throughout animals' lifespans, thus the ability to profit from high food levels may directly influence animal fitness. Studies exploring the link between basal metabolic rate (BMR), growth, reproduction, and other fitness traits have shown varying relationships in terms of both magnitude and direction. The diversity of results has led to the hypothesis that these relationships are modulated by environmental conditions (e.g., food availability), suggesting that the fitness consequences of a given BMR may be context-dependent. In turn, there is indirect evidence that individuals with an increased capacity for aerobic work also have a high capacity for acquiring energy from food. Surprisingly, very few studies have explored the correlation between maximum rates of energy acquisition and BMR in endotherms, and to the best of our knowledge, none have attempted to elucidate relationships between the former and aerobic capacity [e.g., maximum metabolic rate (MMR), aerobic scope (Factorial aerobic scope, FAS; Net aerobic scope, NAS)]. In this study, we measured BMR, MMR, maximum food intake (recorded under low ambient temperature and ad libitum food conditions; MFI), and estimated aerobic scope in the leaf-eared mouse (Phyllotis darwini). We, then, examined correlations among these variables to determine whether metabolic rates and aerobic scope are functionally correlated, and whether an increased aerobic capacity is related to a higher MFI. We found that aerobic capacity measured as NAS is positively correlated with MFI in endotherms, but with neither FAS nor BMR. Therefore, it appears plausible that the capacity for assimilating energy under conditions of abundant resources is determined adaptively by NAS, as animals with higher NAS would be promoted by selection. In theory, FAS is an invariant measurement of the extreme capacity for energy turnover in relation to resting expenditure, whereas NAS represents the maximum capacity for simultaneous aerobic processes above maintenance levels. Accordingly, in our study, FAS and NAS represent different biological variables; FAS, in contrast to NAS, may not constrain food intake. The explanations for these differences are discussed in biological and mathematical terms; further, we encourage the use of NAS rather than FAS when analyzing the aerobic capacity of animals.

Trade-offs between microbiome diversity and productivity in a stratified microbial mat.

Productivity is a major determinant of ecosystem diversity. Microbial ecosystems are the most diverse on the planet yet very few relationships between diversity and productivity have been reported as compared with macro-ecological studies. Here we evaluated the spatial relationships of productivity and microbiome diversity in a laboratory-cultivated photosynthetic mat. The goal was to determine how spatial diversification of microorganisms drives localized carbon and energy acquisition rates. We measured sub-millimeter depth profiles of net primary productivity and gross oxygenic photosynthesis in the context of the localized microenvironment and community structure, and observed negative correlations between species richness and productivity within the energy-replete, photic zone. Variations between localized community structures were associated with distinct taxa as well as environmental profiles describing a continuum of biological niches. Spatial regions in the photic zone corresponding to high primary productivity and photosynthesis rates had relatively low-species richness and high evenness. Hence, this system exhibited negative species-productivity and species-energy relationships. These negative relationships may be indicative of stratified, light-driven microbial ecosystems that are able to be the most productive with a relatively smaller, even distributions of species that specialize within photic zones.

Genome-Wide Association Study in Arabidopsis thaliana of Natural Variation in Seed Oil Melting Point: A Widespread Adaptive Trait in Plants.

Seed oil melting point is an adaptive, quantitative trait determined by the relative proportions of the fatty acids that compose the oil. Micro- and macro-evolutionary evidence suggests selection has changed the melting point of seed oils to covary with germination temperatures because of a trade-off between total energy stores and the rate of energy acquisition during germination under competition. The seed oil compositions of 391 natural accessions of Arabidopsis thaliana, grown under common-garden conditions, were used to assess whether seed oil melting point within a species varied with germination temperature. In support of the adaptive explanation, long-term monthly spring and fall field temperatures of the accession collection sites significantly predicted their seed oil melting points. In addition, a genome-wide association study (GWAS) was performed to determine which genes were most likely responsible for the natural variation in seed oil melting point. The GWAS found a single highly significant association within the coding region of FAD2, which encodes a fatty acid desaturase central to the oil biosynthesis pathway. In a separate analysis of 15 a priori oil synthesis candidate genes, 2 (FAD2 and FATB) were located near significant SNPs associated with seed oil melting point. These results comport with others' molecular work showing that lines with alterations in these genes affect seed oil melting point as expected. Our results suggest natural selection has acted on a small number of loci to alter a quantitative trait in response to local environmental conditions.

Reconstructing the effects of fishing on life-history evolution in North Sea plaice Pleuronectes platessa

Growing evidence suggests that fishing may induce rapid contemporary evolution in certain life-history traits. This study analyzes fisheries-induced changes in life-history traits describing growth, maturation, and reproduction, using an individual-based eco-genetic model that captures both the population dynamics and changes in genetic trait values. The model was successfully calibrated to match the observed life-history traits of female North Sea plaice 'Pleuronectes platessa' around the years 1900 and 2000. On this basis, we report the fllowing findings. First, the model indicates changes in 3 evolving life-history traits: the intercept of the maturation reaction norm decreases by 27%, the weight-specific reproductive-investment rate increases by 10%, and the weight-specific energy-acquisition rate increases by 1%. Together, these changes reduce the weight at maturation by 46% and the asymptotic body weight by 28% relative to the intensification of fishing around 1900. Second, while the maturation reaction norm and reproductive-investment rate change monotonically over time, the energy-acquisition rate follows a more complex course: after an initial increase during the first 50 yr, it remains constant for about 30 yr and then starts to decline. Third, our analysis indicates that North Sea plaice has not yet attained a new evolutionary equilibrium: it must be expected to evolve further towards earlier maturation, increased reproductive investment, and lower adult body size. Fourth, when fishing continues in our model 100 yr into the future, the pace of evolution slows down for the maturation reaction norm and the rate of energy acquisition, whereas no such slowing down is expected for the rate of reproductive investment.

Investigating the mechanisms of amylolysis of starch granules by solution-state NMR.

Starch is a prominent component of the human diet and is hydrolyzed by α-amylase post-ingestion. Probing the mechanism of this process has proven challenging, due to the intrinsic heterogeneity of individual starch granules. By means of solution-state NMR, we demonstrate that flexible polysaccharide chains protruding from the solvent-exposed surfaces of waxy rice starch granules are highly mobile and that during hydrothermal treatment, when the granules swell, the number of flexible residues on the exposed surfaces increases by a factor of 15. Moreover, we show that these flexible chains are the primary substrates for α-amylase, being cleaved in the initial stages of hydrolysis. These findings allow us to conclude that the quantity of flexible α-glucan chains protruding from the granule surface will greatly influence the rate of energy acquisition from digestion of starch.

How salinity and temperature combine to affect physiological state and performance in red knots with contrasting non-breeding environments.

Migratory shorebirds inhabit environments that may yield contrasting salinity-temperature regimes-with widely varying osmoregulatory demands, even within a given species-and the question is: by which physiological means and at which organisational level do they show adjustments with respect to these demands? Red knots Calidris canutus winter in coastal areas over a range of latitudes. The nominal subspecies winters in salty areas in the tropics, whereas the subspecies Calidris canutus islandica winters in north-temperate regions of comparatively lower salinities and temperatures. In this study, both subspecies of red knot were acclimated to different salinity (28/40‰)-temperature (5/35 °C) combinations for 2-week periods. We then measured food/salt intakes, basal metabolic rate (BMR), body mass and temperature, fat and salt gland scores, gizzard mass, heat-shock proteins, heterophils/lymphocytes (H/L) ratio and plasma Na(+) to assess the responses of each taxon to osmoregulatory challenges. High salinity (HS)-warm-acclimated birds reduced food/salt intake, BMR, body mass, fat score and gizzard mass, showing that salt/heat loads constrained energy acquisition rates. Higher salt gland scores in saltier treatments indicated that its size was adjusted to higher osmoregulatory demands. Elevated plasma Na(+) and H/L ratio in high-salinity-warm-acclimated birds indicated that salt/heat loads might have a direct effect on the water-salt balance and stress responses of red knots. Subspecies had little or no effect on most measured parameters, suggesting that most adjustments reflect phenotypic flexibility rather than subspecific adaptations. Our results demonstrate how salinity and temperature affect various phenotypic traits in a migrant shorebird, highlighting the importance of considering these factors jointly when evaluating the environmental tolerances of air-breathing marine taxa.

Acclimating to thermal changes: Intraspecific variation in a small mammal from the Andes Mountains

Ambient temperature strongly affects an ecosystem's characteristics as well as the attributes of individuals, eventually determining the distribution of populations and species. Phenotypic plasticity plays a central role in the administration of energy under thermal variation through traits underlying energy acquisition and expenditure. A powerful approach to assess acclimation ability to environmental variation is studying relevant traits along natural geographic gradients. Our goal was to assess and quantify in the small rodent Phyllotis xanthopygus, changes in traits relevant to energy balance in response to its thermal landscape. We compared energy intake and digestibility by animals from sites at different elevations under different temperatures in the laboratory. Results showed an increase in energy acquisition rates by the lower-elevation individuals to cope with low temperatures, while high-elevation animals appeared unaffected by this treatment. After acclimating to warmer conditions, all individuals showed a similar decrease in energy intake, irrespective of their origin site. We also assessed thermal conductance in individuals from different elevations and found that animals from higher sites exhibited lower heat loss rates. Our evidence suggests that heat conservation differences could in part account for differences among high and low elevation animals in the ability to cope with low temperatures. The lack of plasticity under the warm thermal treatment conforms to recent reports of high conservatism on the upper limit of the thermoneutral zone. P. xanthopygus displays intraspecific variation in the response to temperature, and we propose that this is highly relevant to model its chances in a warming environment.

Spatial variation in growth, maturation schedules and reproductive investment of female sole Solea solea in the Northeast Atlantic

Latitudinal variation in life-history traits is often explained by phenotypically plastic responses or local adaptations to different thermal regimes. We compared growth, maturation schedules and reproductive investment of female sole Solea solea between 8 populations, covering much of the species' distribution in northern Europe, with respect to thermal gradients. An energy allocation model was fitted to size–age data, and probabilistic maturation reaction norms were estimated from size–age–maturity data. We found that northern populations from colder environments had higher rates of energy acquisition and reproductive investment, an intrinsic tendency to mature earlier, and had smaller asymptotic sizes than southern populations from warmer environments. Consequently, growth rate was higher before maturation but lower after maturation in the north compared to the south. This is opposite to Bergmann's rule according to which slower growth, delayed maturation and larger asymptotic sizes are usually observed at lower temperatures. The observed patterns could indicate strong countergradient thermal adaptation for rapid growth and development as well as sustained fecundity in the north, or indicate a response to other selection pressures correlated with the thermal gradient. Potentially higher mortality in northern populations during cold winters might be one of the key drivers of the observed geographical variation in growth and maturation of sole.

Seabird conservation and tidal stream and wave power generation: Information needs for predicting and managing potential impacts

Abstract Current development plans indicate that during the next decade there will be an increase in tidal stream and wave (TSW) power generation activity in Scottish Waters, together with the designation of additional offshore areas for seabird conservation. This paper summarises how TSW developments could affect seabirds, based on experience from other forms of disturbance, and explores the possible changes in behaviour and habitat that have the potential to increase a seabird's rate of energy acquisition (e.g. through enhancing prey abundance), or energy expenditure (e.g. through causing birds to commute further to find food, if they avoid foraging around developments placed in regular feeding areas). Changes to energy budgets could impact rates of reproduction and survival. Simulation modelling of seabird energetics and behaviour is one possible tool for predicting the direction and magnitude of population impacts caused by alterations to energy budgets, but is dependant on the availability and accuracy of necessary parameters. The later sections of the paper review the information needed for such models and shows that although some data are available regarding rates of energy expenditure during specific activities, more information is needed on seabird foraging rates. The paper also highlights how the susceptibility of a species to be impacted by future TSW development is likely to be related to their method of foraging, flight behaviour and ability to buffer against environmental fluctuations.

Aerial surveillance by a generalist seed predator: food resource tracking by Meyer's parrotPoicephalus meyeriin the Okavango Delta, Botswana

Abstract:As a proven food resource generalist, Meyer's parrot (Poicephalus meyeri) was expected to track the availability of all significant food resources in its diet over time. Here we recorded all feeding activity during 366 standardized road transects for correlation with an index of relative food resource abundance over 18 mo. As expected, Meyer's parrot made food resource decisions according to relative abundance at landscape level. Feeding activity on food resources available throughout the year (e.g. ripeKigelia africanafruit) or not visible from the air (e.g. unripeDiospyros lycoidesfruit), however, did not correlate significantly with fluctuations in their relative resource abundance. In addition, over 70% of all feeding bouts were in the high canopy and over 70% of all food items consumed formed bi-coloured displays. The influence of estimated protein and energy acquisition rates from different food resources was insignificant. Therefore, important selection criteria for utilization by Meyer's parrot include relative abundance and visibility from the air (i.e. food resources with the highest probability of encounter when dispersing from a central roost). Sensitivity to fluctuations in resource abundance at landscape level demonstrates the relative importance of maximizing net gain per unit foraging time by minimizing foraging flight distance.

Multiple growth-correlated life history traits estimated simultaneously in individuals

We present a new methodology to estimate rates of energy acquisition, maintenance, reproductive investment and the onset of maturation (four-trait estimation) by fitting an energy allocation model to individual growth trajectories. The accuracy and precision of the method is evaluated on simulated growth trajectories. In the deterministic case, all life history parameters are well estimated with negligible bias over realistic parameter ranges. Adding environmental variability reduces precision, causes the maintenance and reproductive investment to be confounded with a negative error correlation, and tends, if strong, to result in an underestimation of the energy acquisition and maintenance and an overestimation of the age and size at the onset of maturation. Assuming a priori incorrect allometric scaling exponents also leads to a general but fairly predictable bias. To avoid confounding in applications we propose to assume a constant maintenance (three-trait estimation), which can be obtained by fitting reproductive investment simultaneously to size at age on population data. The results become qualitatively more robust but the improvement of the estimate of the onset of maturation is not significant. When applied to growth curves back-calculated from otoliths of female North Sea plaice Pleuronectes platessa, the four-trait and three-trait estimation produced estimates for the onset of maturation very similar to those obtained by direct observation. The correlations between life-history traits match expectations. We discuss the potential of the methodology in studies of the ecology and evolution of life history parameters in wild populations.

Sublethal toxicant effects with dynamic energy budget theory: model formulation

We develop and test a general modeling framework to describe the sublethal effects of pollutants by adding toxicity modules to an established dynamic energy budget (DEB) model. The DEB model describes the rates of energy acquisition and expenditure by individual organisms; the toxicity modules describe how toxicants affect these rates by changing the value of one or more DEB parameters, notably the parameters quantifying the rates of feeding and maintenance. We investigate four toxicity modules that assume: (1) effects on feeding only; (2) effects on maintenance only; (3) effects on feeding and maintenance with similar values for the toxicity parameters; and (4) effects on feeding and maintenance with different values for the toxicity parameters. We test the toxicity modules by fitting each to published data on feeding, respiration, growth and reproduction. Among the pollutants tested are metals (mercury and copper) and various organic compounds (chlorophenols, toluene, polycyclic aromatic hydrocarbons, tetradifon and pyridine); organisms include mussels, oysters, earthworms, water fleas and zebrafish. In most cases, the data sets could be adequately described with any of the toxicity modules, and no single module gave superior fits to all data sets. We therefore propose that for many applications, it is reasonable to use the most general and parameter sparse module, i.e. module 3 that assumes similar effects on feeding and maintenance, as a default. For one example (water fleas), we use parameter estimates to calculate the impact of food availability and toxicant levels on the long term population growth rate.

Seasonal flexibility of organ mass and intestinal function for the Andean lizard Liolaemus nigroviridis

One of the most fundamental questions in organismal ecology is how animals work in a continuously changing environment. In order to contribute to the current understanding of this question, this study evaluated seasonal changes in digestive enzymes activities, organs size, and energy reserves in Liolaemus nigroviridis, a medium-size lizard that inhabit extreme environments in the Andes range. We found that digestive enzymes (trehalase, maltase, and aminopeptidase-N) hydrolytic activities, dry masses of digestive organs and liver, and energy reserve (dry mass of fat bodies and tail energy density) were greater during summer than during winter months. By contrast, dry mass of the kidneys, lungs, heart, and gonads were greater during winter (though significance was reach only for the last two organs). In summary, obtained results reinforce the idea that hibernation is connected with phenotypic adjustments at different organizational levels, which in turn, potentially affects rates of energy acquisition and expenditure, organisms' fitness, and, ultimately, ecological and evolutionary success of species living in highly seasonal environments. We suggest that, owing to the pressing need to explain and predict the impact of climatic change on the biota, more studies destined to determine the levels and limits of physiological flexibility are necessary.

Effect of color vision phenotype on the foraging of wild white-faced capuchins, Cebus capucinus

New World monkeys exhibit a color vision polymorphism. It results from allelic variation of the single-locus middle-to-long wavelength opsin gene on the X chromosome. Females that are heterozygous for the gene possess trichromatic vision. All other individuals possess dichromatic vision. The prevailing hypothesis for the maintenance of the color vision polymorphism is through a consistent fitness advantage to heterozygous trichromatic females. Such females are predicted to be more efficient than dichromats when detecting and selecting fruit. Recent experiments with captive callitrichid primates provided support for this hypothesis by demonstrating that color vision phenotype affects behavioral responses to contrived food targets. Yet, the assumptions that trichromatic females acquire more calories from fruit, or that number of offspring is linked to caloric intake, remain untested. Here, we assess if, in the wild, heterozygous trichromatic individuals in a group of white-faced capuchins (Cebus capucinus) enjoy an energetic advantage over dichromats when foraging on fruit. Contrary to the assumptions of previous theoretical and experimental studies, our analysis of C. capucinus foraging behavior shows that trichromats do not differ from dichromats in their fruit or energy acquisition rates. For white-faced capuchins, the advantage of trichromatic vision may be related to the detection of predators, animal prey, or fruit under mesopic conditions. This result demonstrates the importance of using a fitness currency that is relevant to individual animals to test evolutionary hypotheses.