Resource Allocation Trade-offs Research Articles

Specific carotenoid pigments in the diet and a bit of oxidative stress in the recipe for producing red carotenoid-based signals.

Colorful ornaments have been the focus of sexual selection studies since the work of Darwin. Yellow to red coloration is often produced by carotenoid pigments. Different hypotheses have been formulated to explain the evolution of these traits as signals of individual quality. Many of these hypotheses involve the existence of a signal production cost. The carotenoids necessary for signaling can only be obtained from food. In this line, carotenoid-based signals could reveal an individual’s capacity to find sufficient dietary pigments. However, the ingested carotenoids are often yellow and became transformed by the organism to produce pigments of more intense color (red ketocarotenoids). Biotransformation should involve oxidation reactions, although the exact mechanism is poorly known. We tested the hypothesis that carotenoid biotransformation could be costly because a certain level of oxidative stress is required to correctly perform the conversion. The carotenoid-based signals could thus reveal the efficiency of the owner in successfully managing this challenge. In a bird with ketocarotenoid-based ornaments (the red-legged partridge; Alectoris rufa), the availability of different carotenoids in the diet (i.e. astaxanthin, zeaxanthin and lutein) and oxidative stress were manipulated. The carotenoid composition was analyzed and quantified in the ornaments, blood, liver and fat. A number of oxidative stress biomarkers were also measured in the same tissues. First, we found that color and pigment levels in the ornaments depended on food levels of those carotenoids used as substrates in biotransformation. Second, we found that birds exposed to mild levels of a free radical generator (diquat) developed redder bills and deposited higher amounts of ketocarotenoids (astaxanthin) in ornaments. Moreover, the same diquat-exposed birds also showed a weaker resistance to hemolysis when their erythrocytes were exposed to free radicals, with females also enduring higher oxidative damage in plasma lipids. Thus, higher color production would be linked to higher oxidative stress, supporting the biotransformation hypothesis. The recent discovery of an avian oxygenase enzyme involved in converting yellow to red carotenoids may support our results. Nonetheless, the effect could also depend on the abundance of specific substrate carotenoids in the diet. Birds fed with proportionally higher levels of zeaxanthin showed the reddest ornaments with the highest astaxanthin concentrations. Moreover, these birds tended to show the strongest diquat-mediated effect. Therefore, in the evolution of carotenoid-based sexual signals, a biotransformation cost derived from maintaining a well-adjusted redox machinery could coexist with a cost linked to carotenoid acquisition and allocation (i.e. a resource allocation trade-off).

Multienvironment Evaluation of Pinus pinaster Provenances: Evidence of Genetic Trade-Offs between Adaptation to Optimal Conditions and Resistance to the Maritime Pine Bast Scale (Matsucoccus feytaudi)

Maritime pine (Pinus pinaster Ait.) is currently threatened by the scale insect Matsucoccus feytaudi Duc., which feeds exclusively on this species. Some P. pinaster provenances from the western Mediterranean are known to be resistant to M. feytaudi. The primary resistance mechanism is the existence of anatomical defenses (i.e., resin ducts), but the production of these defenses may come at the cost of resource allocation trade-offs with other functions, including growth. We analyzed a multienvironment trial in central Italy including eight representative provenances of P. pinaster. Trees at one trial were severely attacked by M. feytaudi, whereas those at three trials remained insect-free at tree age 20. Genotype × environment interactions for growth and mortality were analyzed using the additive main effects and multiplicative interaction (AMMI) model. Strong correlations were found between AMMI genotypic scores for tree height and diameter and M. feytaudi nymph density at the infested trial site. In particular, provenances exhibiting specific adaptation to near-optimal conditions showed high susceptibility to the insect; conversely, those origins better adapted to poorer conditions were much less affected by the outbreak. This study demonstrates that a potentially adaptive divergence in aboveground growth among P. pinaster provenances is related to resistance to the insect M. feytaudi.

Costs of reproduction—A demographical approach to examine life-history trade-offs in two old-world deer species

Resource-allocation trade-offs comprise fundamental constraints on life-history evolution. In particular, the trade-offs between reproduction and longevity and between present and future reproduction are believed to be important in shaping reproductive patterns. Unfortunately, exploring such trade-offs in natural populations is complicated and may not be possible in all taxa. Against this background we here use zoo data for enhancing our understanding of reproductive patterns in two endangered and cryptic deer species (Vietnamese sika deer Cervus nippon pseudaxis, Mesopotamian fallow deer Dama dama mesopotamica). In both species, births peaked right before the onset of the rainy season in the species’ natural environments. Females reached high reproductive output earlier in life and had (in one species only) higher survival rates than males. Offspring number covaried positively rather than negatively with longevity. In females, the length of the reproductive phase correlated positively with longevity, birth rate within the entire lifespan, and offspring number, while it was negatively related to the birth rate during the reproductive phase (in 1 species). The length of the post-reproductive phase was positively related to longevity and negatively to the birth rate during the entire lifespan. Taken together, we revealed several patterns being presumably of ecological relevance including indications for trade-offs among offspring quality and quantity, and between present and future reproduction even within these captive populations relieved from seasonal (e.g. food) constraints. In spite of some limitations, our study reconfirms that zoo data offer insights into the reproductive biology of species for which field data are difficult to obtain.

Impaired sperm quality, delayed mating but no costs for offspring fitness in crickets winning a fight.

The outcome of male-male contest competition is known to affect male mating success and is believed to confer fitness benefits to females through preference for dominant males. However, by mating with contest winners, females can incur significant costs spanning from decreased fecundity to negative effects on offspring. Hence, identifying costs and benefits of male dominance on female fitness is crucial to unravel the potential for a conflict of interests between the sexes. Here, we investigated males' pre- and post-copulatory reproductive investment and its effect on female fitness after a single contest a using the field cricket Gryllus bimaculatus. We allowed males to fight and immediately measured their mating behaviour, sperm quality and offspring viability. We found that males experiencing a fight, independently of the outcome, delayed matings, but their courtship effort was not affected. However, winners produced sperm of lower quality (viability) compared to losers and to males that did not experience fighting. Results suggest a trade-off in resource allocation between pre- and post-mating episodes of sexual selection. Despite lower ejaculate quality, we found no fitness costs (fecundity and viability of offspring) for females mated to winners. Overall, our findings highlight the importance of considering fighting ability when assessing male reproductive success, as winners may be impaired in their competitiveness at a post-mating level.

Sex and migratory strategy influence corticosterone levels in winter-grown feathers, with positive breeding effects in a migratory pelagic seabird.

To overcome unpredictable stressful transitory events, animals trigger an allostatic response involving the hypothalamic-pituitary-adrenal cortex. This hormonal response, which involves the release of glucocorticoids which in turn mediate between the main physiological mechanisms that regulate the energetic demands and resource allocation trade-off with behavioural responses to environmental perturbations and may ultimately lead to variation in fitness. We have used the Cory's shearwater Calonectris borealis, a sexually dimorphic pelagic seabird with a partial migratory strategy, as a model bird species to analyse a number of traits related to the stress response. We investigated whether the activation of a stressful response, mediated by corticosterone, during the wintering period (1) correlated with the previous breeding success, (2) was affected by the migratory behaviour of male birds and (3) had consequences in the fitness of the birds. Corticosterone levels in feathers grown overwinter were analysed in 61 adult birds during three consecutive migratory periods (2009-2012) and in 14 immature birds in the wintering period 2010-2011. Moreover, the levels of corticosterone were analysed in experimental birds which were freed from their reproductive duties and compared with control birds which raised fledglings to the end of the breeding period. The results show that the levels of corticosterone were sex dependent, differed between years and were affected by the migratory strategy performed by the birds. The activation of the stressful response over the wintering period generated residual carry-over effects that positively affected the reproductive output in the subsequent breeding stage, a phenomenon previously undescribed in a long-lived pelagic seabird. Our study provides evidence that the analysis of corticosterone from feathers is a useful tool to evaluate carry-over effects in birds far away from breeding sites, opening new possibilities for future studies in this field.

Early developmental exposures shape trade-offs between acquired and innate immunity in humans.

Life history theory predicts resource allocation trade-offs between competing functions and processes. We test the hypothesis that relative investment towards innate versus acquired immunity in humans is subject to such trade-offs and that three types of early developmental exposures are particularly salient in shaping adult immunophenotype: (i) pathogen exposure, (ii) nutritional resources; and (iii) extrinsic mortality cues. We quantified one aspect each of innate and acquired immune function, via C-reactive protein and Epstein-Barr virus antibodies, respectively, in a sample of 1248 men and women from the Philippines (ca. 21.5 years old). Early developmental exposures were assessed via long-term data collected prospectively since participants' birth (1983-4). We calculated a standardized ratio to assess relative bias towards acquired versus innate immune function and examined its relationship to a suite of predictors via multiple regression. In partial support of our predictions, some of the measures of higher pathogen exposure, greater availability of nutritional resources, and lower extrinsic mortality cues in early life were associated with a bias toward acquired immunity in both men and women. The immune profile of women, in particular, appeared to be more sensitive to early life pathogen exposures than those of men. Finally, contrary to prediction, women exhibited a greater relative investment toward innate, not acquired, immunity. Early environments can exert considerable influence on the development of immunity. They affect trade-offs between innate and acquired immunity, which show adaptive plasticity and may differ in their influence in men and women.

Have male trees of the tropical rain forest evolved to minimize the interactions with mycorrhizal symbionts?

While arbuscular mycorrhizal fungi improve plant performance they demand large shares of the plant's assimilated carbon, therefore resource allocation trade-offs may drive the commonly observed sexual dimorphism in mycorrhizal colonization in dioecious species. Here we looked for evidence of the evolutionary reduction of mycorrhizal colonization in males of 15 tropical rain forest plants including palms (Chamaedorea) and trees, light-demanding and shade-tolerant species. For none of the analyzed species there was evidence of spatial segregation of the sexes. Most of the tree species had no seasonal variability in mycorrhizal colonization and males had lower mycorrhizal colonization than females in over 70% of the tree species. In contrast, there were no differences between the sexes of the Chamaedorea species. Chamaedorea species had ticker roots and lower specific root length than trees, and seasonal patterns of mycorrhizal colonization correlated with the life-histories of the plants. Based on phylogenetically independent contrast, mycorrhizal colonization of male trees correlated negatively with a metric of sexual differentiation of mycorrhizal colonization between sexes. Our results suggest an evolutionary reduction in the intensity of mycorrhizal interactions in male plants, presumably driven by resource allocation trade-offs as the origen of sexual dimorphs in mycorrhizal colonization.

Development of a metabolite-driven daphnia ecophysiological model

One of the founding principles of modern aquatic ecology is that human-induced perturbations in the autotroph-herbivore interface have the potential to affect ecological processes at higher trophic levels. Thus, zooplankton’s physiological state can be an early warning sign of broader impairments of aquatic ecosystems. Based on this reasoning, the micro-crustacean Daphnia is often identified as a keystone freshwater species, but its bioenergetic motivations and physiological priorities remain only partially understood. Using a bioenergetically explicit ecophysiological approach, we model how trade-offs in resource allocation can shape a daphnid's growth. Our multi-faceted hierarchical approach to metabolite utilization challenges the popular paradigm of elemental stoichiometry being the primary regulatory factor of algal food quality. We examine the post-gut bioenergetic ramifications of an unbalanced diet, showing that animal growth can be significantly compromised by the elevated energetic requirements of homeostasis. Our modeling framework offers an excellent stepping-stone to connect zooplankton physiological processes with the signals of external stressors, and subsequently evaluate the patterns of mass and energy flow at an ecosystem scale. The proposed microscopic-to-macroscopic strategy will likely offer a new prospect towards the development of early warning systems for the management of freshwater resources.

Effects of food availability on asexual reproduction and stress tolerance along the fast–slow life history continuum in freshwater hydra (Cnidaria: Hydrozoa)

Life history theory predicts that reproduction and somatic maintenance are negatively related, but the strength of this relationship is expected to depend on food availability. In this study, we investigated asexual reproduction (budding rate) and oxidative stress tolerance as two opposing facets of life history trade-offs in 17 strains of five freshwater hydra species under experimentally simulated low, medium, and high food availability. Stress tolerance was quantified by exposing animals to exogenous H2O2, which mimics reactive oxygen species arising in vivo. The five species differed in life history traits (low budding rate and high stress tolerance in Hydra vulgaris and H. circumcincta and the opposite in H. oligactis and H. viridissima; low budding rate combined with relatively low stress tolerance in H. oxycnida). Stress tolerance and asexual reproduction increased with food, but there were clear interspecific differences in this relationship. Across all strains, stress tolerance and budding rate were significantly negatively related on the low and medium, but not the high food level. These results suggest that resource allocation trade-offs are involved in determining life history traits in hydra; populations/species can be broadly positioned on a fast–slow life history continuum, and response to variation in food varies along this continuum.

Optimal Resource Allocation and EE-SE Trade-Off in Hybrid Cognitive Gaussian Relay Channels

Recent literature has suggested the benefits of integrating licensed radio and cognitive radio into a hybrid cooperative communication system. The fundamental properties of such hybrid systems, however, have not been thoroughly investigated. This paper studies the hybrid cognitive Gaussian relay channel (HCGRC), which uses licensed radio resource (RR) and cognitive/unlicensed RR for forward and relay transmissions, respectively. HCGRC fundamentally differs from conventional relay channels in that the licensed and cognitive RRs are not subject to a total resource constraint and that the cognitive RR is opportunistic in nature. With respect to both the upper and lower bounds, we derive the optimal power-bandwidth allocation strategies for the cognitive relay to maximize the capacity, spectrum efficiency (SE), and energy efficiency (EE). The Pareto-optimal EE-SE tradeoff curve is also derived analytically. Our study leads to two key observations. First, the multi-objective power-bandwidth allocation problem is characterized by five regions, each representing a unique performance tradeoff. Second, the reliability of cognitive RR has no impact on the EE-SE tradeoff given unlimited bandwidth and power.

Adaptive plasticity and niche expansion in an invasive thistle.

Phenotypic differentiation in size and fecundity between native and invasive populations of a species has been suggested as a causal driver of invasion in plants. Local adaptation to novel environmental conditions through a micro-evolutionary response to natural selection may lead to phenotypic differentiation and fitness advantages in the invaded range. Local adaptation may occur along a stress tolerance trade-off, favoring individuals that, in benign conditions, shift resource allocation from stress tolerance to increased vigor and fecundity and, therefore, invasiveness. Alternately, the typically disturbed invaded range may select for a plastic, generalist strategy, making phenotypic plasticity the main driver of invasion success. To distinguish between these hypotheses, we performed a field common garden and tested for genetically based phenotypic differentiation, resource allocation shifts in response to water limitation, and local adaptation to the environmental gradient which describes the source locations for native and invasive populations of diffuse knapweed (Centaurea diffusa). Plants were grown in an experimental field in France (naturalized range) under water addition and limitation conditions. After accounting for phenotypic variation arising from environmental differences among collection locations, we found evidence of genetic variation between the invasive and native populations for most morphological and life-history traits under study. Invasive C. diffusa populations produced larger, later maturing, and therefore potentially fitter individuals than native populations. Evidence for local adaptation along a resource allocation trade-off for water limitation tolerance is equivocal. However, native populations do show evidence of local adaptation to an environmental gradient, a relationship which is typically not observed in the invaded range. Broader analysis of the climatic niche inhabited by the species in both ranges suggests that the physiological tolerances of C. diffusa may have expanded in the invaded range. This observation could be due to selection for plastic, “general-purpose” genotypes with broad environmental tolerances.

Energy allocation during the maturation of adults in a long-lived insect: implications for dispersal and reproduction.

Energy allocation strategies have been widely documented in insects and were formalized in the context of the reproduction process by the terms 'capital breeder' and 'income breeder'. We propose here the extension of this framework to dispersal ability, with the concepts of 'capital disperser' and 'income disperser', and explore the trade-off in resource allocation between dispersal and reproduction. We hypothesized that flight capacity was sex-dependent, due to a trade-off in energy allocation between dispersal and egg production in females. We used Monochamus galloprovincialis as model organism, a long-lived beetle which is the European vector of the pine wood nematode. We estimated the flight capacity with a flight mill and used the number of mature eggs as a proxy for the investment in reproduction. We used the ratio between dry weights of the thorax and the abdomen to investigate the trade-off. The probability of flying increased with the adult weight at emergence, but was not dependent on insect age or sex. Flight distance increased with age in individuals but did not differ between sexes. It was also positively associated with energy allocation to thorax reserves, which increased with age. In females, the abdomen weight and the number of eggs also increase with age with no negative effect on flight capacity, indicating a lack of trade-off. This long-lived beetle has a complex strategy of energy allocation, being a 'capital disperser' in terms of flight ability, an 'income disperser' in terms of flight performance and an 'income breeder' in terms of egg production.

Causes of Discordance between Allometries at and above Species Level: An Example with Aquatic Beetles.

Covariation among organismal traits is nearly universal, occurring both within and among species (static and evolutionary allometry, respectively). If conserved developmental processes produce similarity in static and evolutionary allometry, then when species differ in development, it should be expressed in discordance between allometries. Here, we investigate whether rapidly evolving developmental processes result in discordant static and evolutionary allometries attributable to trade-offs in resource acquisition, allocation, or growth across 30 species of aquatic beetles. The highly divergent sperm phenotypes of these beetles might be an important contributor to allometric evolution of testis and accessory gland mass through altered requirements for the production of sperm and seminal fluids. We documented extensive discordance between static and evolutionary allometries, indicating that allometric relationships are flexibly modified over short time periods but subject to constraint over longer time spans. Among species, sperm phenotype did not influence relative investment in accessory glands but was weakly associated with investment in testes. Furthermore, except when sperm were long and simple, sperm phenotype was not associated with species-specific modification of the allometry of testis/accessory gland mass and body size. Our results demonstrate the utility of allometric discordance to infer species differences in the provisioning and growth of concurrently developing traits.

Effects of Tail Clipping on Larval Performance and Tail Regeneration Rates in the Near Eastern Fire Salamander, Salamandra infraimmaculata.

Tail-tip clipping is a common technique for collecting tissue samples from amphibian larvae and adults. Surprisingly, studies of this invasive sampling procedure or of natural tail clipping – i.e., bites inflicted by predators including conspecifics - on the performance and fitness of aquatic larval stages of urodeles are scarce. We conducted two studies in which we assessed the effects of posterior tail clipping (~30 percent of tail) on Near Eastern fire salamander (Salamandra infraimmaculata) larvae. In a laboratory study, we checked regeneration rates of posterior tail-tip clipping at different ages. Regeneration rates were hump-shaped, peaking at the age of ~30 days and then decreasing. This variation in tail regeneration rates suggests tradeoffs in resource allocation between regeneration and somatic growth during early and advanced development. In an outdoor artificial pond experiment, under constant larval densities, we assessed how tail clipping of newborn larvae affects survival to, time to, and size at metamorphosis. Repeated measures ANOVA on mean larval survival per pond revealed no effect of tail clipping. Tail clipping had correspondingly no effect on larval growth and development expressed in size (mass and snout-vent length) at, and time to, metamorphosis. We conclude that despite the given variation in tail regeneration rates throughout larval ontogeny, clipping of 30% percent of the posterior tail area seems to have no adverse effects on larval fitness and survival. We suggest that future use of this imperative tool for the study of amphibian should take into account larval developmental stage during the time of application and not just the relative size of the clipped tail sample.

Regulation of feeding behavior and plasma testosterone in response to central neuropeptide Y administration in a songbird.

In mammalian and avian model species, neuropeptide Y (NPY) simultaneously promotes feeding behavior and suppresses the secretion of reproductive hormones, thereby modulating the resource allocation trade-off between investing in essential somatic processes or in the reproductive system. Investigations into this dual role of NPY in birds have focused on domesticated species and, to our knowledge, no study has examined this role in songbirds. We determined whether NPY treatment acutely regulates feeding behavior and activity of the reproductive system in a male songbird, the Abert's Towhee, Melozone aberti. Intracerebroventricular (ICV) administration of NPY promoted behaviors associated with feeding (decreased latency to initiate pecking in the food bowl, increased number of feeding bouts following treatment, and increased number of pecks into the food bowl during each feeding bout), and it stimulated hopping and drinking behavior. By contrast, we found no effect of NPY treatment on plasma testosterone secretion 60 min after treatment. These results suggest that in male Abert's Towhees NPY stimulates feeding behavior, but provide no evidence that this peptide concurrently influences testosterone secretion.

Is diversification in male reproductive traits driven by evolutionary trade-offs between weapons and nuptial gifts?

Many male animals have evolved exaggerated traits that they use in combat with rival males to gain access to females and secure their reproductive success. But some male animals invest in nuptial gifts that gains them access to females. Both these reproductive strategies are costly in that resources are needed to produce the weapon or nuptial gift. In closely related species where both weapons and nuptial gifts are present, little is known about the potential evolutionary trade-off faced by males that have these traits. In this study, we use dobsonflies (order Megaloptera, family Corydalidae, subfamily Corydalinae) to examine the presence and absence of enlarged male weapons versus nuptial gifts within and among species. Many dobsonfly species are sexually dimorphic, and males possess extremely enlarged mandibles that they use in battles, whereas in other species, males produce large nuptial gifts that increase female fecundity. In our study, we show that male accessory gland size strongly correlates with nuptial gift size and that when male weapons are large, nuptial gifts are small and vice versa. We mapped weapons and nuptial gifts onto a phylogeny we constructed of 57 species of dobsonflies. Our among-species comparison shows that large nuptial gift production evolved in many species of dobsonfly but is absent from those with exaggerated weapons. This pattern supports the potential explanation that the trade-off in resource allocation between weapons and nuptial gifts is important in driving the diversity of male mating strategies seen in the dobsonflies, whereas reduced male-male competition in the species producing large spermatophores could be an alternative explanation on their loss of male weapons. Our results shed new light on the evolutionary interplay of multiple sexually selected traits in animals.

Modelling coral calcification accounting for the impacts of coral bleaching and ocean acidification

Abstract. Coral reefs are diverse ecosystems that are threatened by rising CO2 levels through increases in sea surface temperature and ocean acidification. Here we present a new unified model that links changes in temperature and carbonate chemistry to coral health. Changes in coral health and population are explicitly modelled by linking rates of growth, recovery and calcification to rates of bleaching and temperature-stress-induced mortality. The model is underpinned by four key principles: the Arrhenius equation, thermal specialisation, correlated up- and down-regulation of traits that are consistent with resource allocation trade-offs, and adaption to local environments. These general relationships allow this model to be constructed from a range of experimental and observational data. The performance of the model is assessed against independent data to demonstrate how it can capture the observed response of corals to stress. We also provide new insights into the factors that determine calcification rates and provide a framework based on well-known biological principles to help understand the observed global distribution of calcification rates. Our results suggest that, despite the implicit complexity of the coral reef environment, a simple model based on temperature, carbonate chemistry and different species can give insights into how corals respond to changes in temperature and ocean acidification.

Prospective memory function in late adulthood: affect at encoding and resource allocation costs.

Some studies have found that prospective memory (PM) cues which are emotionally valenced influence age effects in prospective remembering, but it remains unclear whether this effect reflects the operation of processes implemented at encoding or retrieval. In addition, none of the prior ageing studies of valence on PM function have examined potential costs of engaging in different valence conditions, or resource allocation trade-offs between the PM and the ongoing task. In the present study, younger, young-old and old-old adults completed a PM task in which the valence of the cues varied systematically (positive, negative or neutral) at encoding, but was kept constant (neutral) at retrieval. The results indicated that PM accuracy did not vary as a function of affect at encoding, and that this effect did not interact with age group. There was also no main or interaction effect of valence on PM reaction time in PM cue trials, indicating that valence costs across the three encoding conditions were equivalent. Old-old adults’ PM accuracy was reduced relative to both young-old and younger adults. Prospective remembering incurred dual-task costs for all three groups. Analyses of reaction time data suggested that for both young-old and old-old, these costs were greater, implying differential resource allocation cost trade-offs. However, when reaction time data were expressed as a proportional change that adjusted for the general slowing of the older adults, costs did not differ as a function of group.

Reproduction and vegetative growth in the dioecious shrub Acer barbinerve in temperate forests of Northeast China.

Trade-off in dioecious plant. The trade-off between reproduction, vegetative growth and maintenance is a major issue in the life history of an organism and a record of the process which is producing the largest possible number of living offspring by natural selection. Dioecious species afford an excellent opportunity for detecting such possible trade-offs in resource allocation. In this study, we selected the dioecious shrub Acer barbinerve to examine possible trade-offs between reproduction and vegetative growth in both genders at different modular levels during three successive years. Reproductive and vegetative biomass values were assessed during successive years to evaluate their intra-annual and inter-annual trade-offs. These trade-offs were examined at shoot, branch and shrub modular levels in Acer barbinerve shrubs. An intra-annual trade-off was detected at the shoot level for both genders in 2011 and 2012. Both males and females showed a negative correlation between reproduction and vegetative growth, but this was more prominent in males. For the females of the species, inter-annual trade-offs were only found at branch and shrub levels. Slightly negative correlations in females were detected between the reproduction in 2012 and the reproduction in the two previous years. The gender ratio was significantly male biased during the three successive years of our investigation. Females had higher mortality rates in the larger diameter classes, both in 2011 and 2012. This study revealed a clear trade-off between reproduction and vegetative growth in Acer barbinerve, but results varied between males and females. The degree of autonomy of the different modular levels may affect the ability to detect such trade-offs.

Does lactation lead to resource allocation trade-offs in the spotted hyaena?

Life history theory predicts that when food intake and body reserves are insufficient to maintain all life processes, resource allocation trade-offs should occur. Lactation is costly and requires increased food intake. In spotted hyaenas, energy expenditure on lactation is high, particularly for mothers rearing twin litters, and foraging effort and food intake are influenced by social status. We investigated whether lactation in this species results in a reduction in resource allocation to immune processes sufficient to increase parasite infection. We expected higher parasite infection in lactating than non-lactating females, in mothers nursing twin than singleton litters, in females of lower than higher social status and in less than more experienced foragers. We quantified Ancylostoma egg load (AEL) and the presence of oocysts of Cystoisospora spp. as a proxy measure of immune function in 58 females. Lactating females were significantly more often infected with Ancylostoma, and their AEL was higher than in non-lactating females. Females nursing twins had significantly higher AELs than those nursing singletons. As social status increased, AELs significantly declined. This relationship was modulated by lactation status and litter size, being strongest in non-lactating females, moderate in females with twin litters and weakest in females with singleton litters. The decrease in AEL with increasing social status was greater for experienced than inexperienced females. Concurrent infection with Cystoisospora significantly increased with increasing AEL. Our results provide evidence for a resource allocation trade-off in lactating spotted hyaenas.