High Physiological Cost Research Articles

An Integrated Biomarker Approach Using Flounder to Improve Chemical Risk Assessments in the Heavily Polluted Seine Estuary.

The objective of this study was to develop an integrative approach in ecotoxicology (from biomarkers to population genetics) to assess the ecological status of fish populations. Flounders (Platichthys flesus) collected after the spawning season in the heavily polluted Seine estuary were compared with the moderately polluted Bay of Douarnenez. The muscle energetic reserves were highly depleted in Seine vs. Douarnenez fish. The Seine fish displaying a reduced capacity to manage the oxidative stress and a higher energetic metabolism. An increase in the content of muscle membrane phospholipids (sphingomyelin, phosphatidylserine, free sterols) was detected in the Seine vs. Douarnenez fish. The data integration allowed to hypothesize relationships between membrane phospholipids, xenobiotic metabolism, bioenergetics, and antioxidant defence. The genetic diversity considering neutral markers was maintained in the heavily polluted Seine population compared with the Douarnenez population. Finally, we suggest that the high physiological cost of tolerance to toxicants in the Seine flounder population could compromise its capacity to respond in the future to an additional stressor like warming waters in shallow depth. Thus, this population could be submitted to an ecological risk.

What factors influence the occurrence of Cubitermes pallidiceps in miombo woodlands in southwestern Burundi?

In Africa, not only large number of termite species remain to be described, but also ecological studies on the termite fauna of the continent are scarce. For instance, the mechanisms underlying termite mounds distribution in ecosystems stay poorly known. The main goal of this study was to assess what determines the distribution of soil-feeding termites playing an important role in the recycling of organic matter. The case of Cubitermes pallidiceps (Sjöstedt) (Isoptera: Cubitermitinae) was taken as a model. In Rumonge Forest, a woodland miombo of 600 ha in southwestern Burundi, we collected soil samples and data on tree density and diameter in 18 sites, six of which were home to mounds of C. pallidiceps. Multiple logistic regressions were used to evaluate the influence of soil properties and elevation on the occurrence of C. pallidiceps. Spatial autocorrelation structure in the model residuals was corrected by the integration of selected spatial predictors generated with the Moran’s eigenvectors maps (MEM) method. C. pallidiceps was present in areas where the tree density was low, therefore with a more opened canopy, probably to avoid fires. Those areas would also provide it a favourable microclimate through direct solar radiation. It was absent in stony places such as hill tops, probably because of food limitation. Soil with high sand content and the highest measured clay content seemed to favour Cubitermes occurrence. Its distribution was also influenced by undetermined spatially structured variables, which could correspond to unmeasured environmental variables such as soil nutrient or toxic elements, or variables related to dispersal abilities or biotic interactions with other species. Our results suggested that soil termites would have evolved in miombo ecosystems to avoid areas with a high physiological and physical cost. Understanding ecological adaptation of soil termites in this stressful environment is important for restoration and management of their habitats.

DYNAMICS AND DIFFERENCES OF BIOCHEMICAL PROFILE OF ATHLETES IN VARIOUS PHASES OF MIDDLE MOUNTAIN TRAINING COMPARED TO SEA LEVEL TRAINING

Aim. The purpose of the article is to study the dynamics of responses and the current state of the body of highly skilled athletes by indicators of the biochemical profile during adaptation to natural hypobaric hypoxia. Materials and methods. The dynamics of 16 biochemical indicators was compared at similar stages of the annual training conducted in middle mountain areas (~ 1550 m) and at sea level. Fifteen female biathlon athletes of the Russian national team participated in the study. The following methods were used: analysis of morning hematological and biochemical indicators of blood during 3 mid-mountain and 4 lowland sports training events. Training loads were recorded. Results. With a comparable level and type of loads, middle mountain training leads to significant (P <0.05) positive shifts in hematological indicators (hemoglobin, hematocrit), starting from the 2nd and 3rd phases of adaptation. In the same period, the level of cortisol and urea rises. Aminotransferases (ALT, AST), on the contrary, are more reactive in the phase of acute acclimatization (P <0.05). There were no signs of a more significant deterioration in the anabolic support of the training process in terms of testosterone. In middle mountain areas, on average, there is a decreased level of phosphorus and iron and an increased level of calcium, as well as a reduced level of muscle tissue damage compared to training at sea level. Conclusion. The dynamics of biochemical indicators in the middle mountain areas and at sea level is similar, this may be a consequence of responses to the load. At the same time, training in the middle mountain areas has a high physiological cost with positive changes in oxygen transport systems. The obtained dynamics and differences in the studied indicators in the phases of middle mountain training can be used to improve the training loads of athletes in cyclic sports.

Upstream migration without complete osmoregulatory switching in an amphidromous goby: Estimated by body condition changes in different salinity environment

The floating goby Gymnogobius petschiliensis Rendahl is an amphidromous fish, which migrates upstream from the sea in the juvenile period and then inhabits not only freshwater areas but also brackish water. Most of the species that have such migratory polymorphism switch their osmoregulatory mechanism in synchrony with the timing of migration, but in G. petschiliensis it is known that even individuals living in freshwater areas behaviourally prefer brackish water to freshwater conditions in a laboratory. To clarify whether this species lives in freshwater areas with high osmoregulatory cost, the relationship between physiological cost and salinity was investigated using adult fish of the species captured in a freshwater area. Adults were kept individually in 13 L tanks with various salinity levels under fasted conditions. Their loss of body weight in freshwater conditions was more rapid than in 2/3 seawater, whereas the frequencies of horizontal and vertical movement in 13 L tanks did not differ significantly between freshwater and 2/3 seawater conditions. This suggests that the weight loss reflects not behavioural performance but physiological cost. In addition, no adults died even when transferred from freshwater to seawater conditions, indicating that they have high tolerance to salinity change in estuarine areas even after migrating to freshwater areas. These results support the hypothesis that G. petschiliensis migrates to freshwater areas while maintaining high hypo-osmoregulatory ability and paying a high physiological cost. Because G. petschiliensis phylogenetically originates from the coastal species, this example of migration without completely switching the osmoregulatory mechanism may help us to understand the diverse processes of upstream migration in marine fish.

Experimental increase in eviction load does not impose a growth cost for cuckoo chicks

Chicks of many avian brood parasites evict their hosts’ eggs within 48 h of hatching. This behavior eliminates competition inside the nest and is beneficial for the fitness of the parasite. Several studies have proposed that this behavior is costly for the parasitic chick and may limit opportunities for cuckoos to exploit hosts with large clutch sizes. We tested whether increased eviction effort was associated with reduced growth in cuckoo chicks by artificially increasing the clutch size of superb fairy-wrens, the main host of the Horsfield’s bronze-cuckoo in Australia. Contrary to theoretical predictions, chicks that evicted a larger number of eggs did not lose mass. Instead, they had higher growth rates than chicks that evicted fewer eggs. This unexpected result suggests chicks might be able to use compensatory growth to overcome the costs of egg eviction, perhaps by increasing their begging rate after evicting more eggs. Our results, combined with previous evidence, suggest that brood parasites may not be constrained by the clutch size of their hosts, resulting in a broader set of potential hosts. Furthermore, laying larger clutches might not be an effective host defense against brood parasites. Avian brood parasites lay their eggs in the nests of other species. Many parasitic chicks, like cuckoos, avoid competition inside the nest by evicting all the other eggs laid by the host. It is generally assumed that this innate behavior is costly for the cuckoo chick, and that evicting more eggs requires greater effort and higher physiological costs. In this study, we use the system of the superb fairy-wren and the Horsfield’s bronze-cuckoo in Australia to test whether evicting more eggs results in decreased growth in parasitic cuckoos. We found no evidence to suggest that evicting more eggs compromises growth in Horsfield’s bronze-cuckoos. In fact, chicks that evicted more eggs grew significantly faster than chicks that evicted fewer eggs, suggesting that chicks are able to compensate for the initial effort of evicting more eggs.

Male territorial aggression and fitness in collared flycatchers: a long-term study

Aggressive behaviour plays a fundamental role in the distribution of limiting resources. Thereby, it is expected to have consequences for fitness. Here, we explored the relationship between aggression and fitness in a long-term database collected in a wild population of the collared flycatcher (Ficedula albicollis). We quantified the aggression of males during nest-site defence by conducting simulated territorial intrusions in the courtship period. We estimated the fitness of males based on their pairing success, breeding output and survival to next year. Earlier arriving and older males had a higher probability to establish pair-bond, and males that started to breed earlier fledged more young. Aggression did not predict pairing and breeding performances. However, the probability of a male to return in the next year was significantly related to aggression in an age-dependent manner. Among subadult males, more aggressive individuals had higher chances to return, while among adult males, less aggressive ones did so. This finding is in harmony with our general observation that subadult collared flycatcher males behave more aggressively than adult males when confronted with a conspecific intruder. Subadult males may be socially inexperienced, so they should be more aggressive to be successful. In contrast, if adult males suffer from higher physiological costs, a lower level of aggression may be more advantageous for them. Our study shows that aggressive behaviour can be a fitness-related trait, and to understand its role in determining fitness, age should be taken into account.

Evolutionary constraints on polyembryony in parasitic wasps: a simulation model

Polyembryony involves the production of several genetically identical progeny from a single egg through clonal division. Although polyembryonic development allows highly efficient reproduction, especially in some parasitoid wasps, it is far less common than monoembryony (development of one embryo per egg). To understand what might constrain the evolutionary success of polyembryony in parasitoids, we developed Monte Carlo models that simulate the competition between polyembryonic females and their monoembryonic counterparts. We investigated which simulated life‐history traits of the females allow the monoembryonic mode of development to succeed. Published empirical studies were surveyed to explore whether these traits indeed differ between polyembryonic parasitoids and related monoembryonic species. The simulations predict an advantage to monoembryony in parasitoids whose reproduction is limited by host availability rather than by egg supply, and that parasitize small‐bodied hosts. Comparative data on the parasitoid families Encyrtidae and (to a lesser extent) Braconidae, but not the data from Platygastridae, circumstantially support these predictions. The model also predicts monoembryony to outcompete polyembryony when: 1) hosts vary considerably in quality, 2) polyembryonic development carries high physiological costs, and 3) monoembryonic females make optimal clutch size decisions upon attacking hosts. These multiple constraints may account for the rarity of polyembryony among parasitoid species.

Morph-Specific Patterns of Reproductive Senescence: Connections to Discrete Reproductive Strategies.

How reproductive strategies contribute to patterns of senescence in natural populations remains contentious. We studied reproductive senescence in the dimorphic white-throated sparrow, an excellent species for exploring this issue. Within both sexes the morphs use distinct reproductive strategies, and disassortative pairing by morph results in pair types with distinct parental systems. White morph birds are more colorful and aggressive than tan counterparts, and white males compete for extrapair matings, whereas tan males are more parental. Tan males and white females share parental care equally, whereas white males provide little parental support to tan females. We found morph-specific patterns of reproductive senescence in both sexes. White males exhibited greater reproductive senescence than tan males. This result likely reflects the difficulty of sustaining a highly competitive reproductive strategy as aging progresses rather than high physiological costs of competitiveness, since white males were also long-lived. Moreover, morph was not consistently related to reproductive senescence across the sexes, arguing against especially high costs of the traits associated with white morph identity. Rather, tan females exhibited earlier reproductive senescence than white females and were short-lived, perhaps reflecting the challenges of unsupported motherhood. Results underscore the importance of social dynamics in determining patterns of reproductive senescence.

Drought‐adapted plants dramatically downregulate dinitrogen fixation: Evidences from Mediterranean legume shrubs

Abstract The importance of symbiotic dinitrogen (N2) fixation in shaping the coupled nitrogen–carbon cycle is now known for most humid terrestrial ecosystems. However, whether N2 fixation can play a key role in the nitrogen and carbon budget of water‐limited and seasonally dry ecosystems remains a mystery. The maintenance of metabolically and physiologically costly symbiotic fixation in water‐limited environments is highly complex. These costs are particularly high during the first developmental season, when allocation to deep rooting and drought resistance mechanisms is essential for seedling survival of prolonged seasonal drought. We, therefore, evaluated how drought‐adapted legume species change their allocation to symbiotic nitrogen fixation as a function of soil nitrogen availability. We tested this on seedlings of a suite of four common Mediterranean legume shrubs with a strong seasonal behaviour, which we grew under controlled nitrogen and phosphorus availabilities. We asked: (1) Do species differ in their investment and regulation of nitrogen fixation? (2) Is fixation regulated via plant allocation to nodules, fixation rate or both? and (3) Does phosphorus availability limit symbiotic nitrogen fixation? All Mediterranean perennial legumes in the experiment established and grew, nodulated, and fixed nitrogen, even under severe nitrogen limitation. The four species reacted similarly to nitrogen supply, by strongly downregulating fixation through both decreased nodulation and lower rate of fixation. However, we found a significant interspecific difference in fixation (both nodulation and rate), biomass production and growth rate. Our experimental species presented a range of fixation investment strategies corresponding to life‐history and resource partitioning patterns. Phosphorus limitation had a minor influence on both fixation and plant growth. Synthesis. The high physiological cost of symbiotic fixation imposes the need to tightly regulate fixation in perennial legumes coping with severe water stress. Control of fixation allows legume species to colonize recently disturbed nitrogen‐deficient habitats, cope with grazing, survive long seasonal droughts and recover nitrogen fixation later in the wet season, and survive over time by reducing nitrogen inputs to the ecosystem.

Dynamics of energy reserves and the cost of reproduction in female and male fiddler crabs

The physiological costs of reproduction can be measured as the energy allocated to reproductive activities. In fiddler crabs, females allocate energy to vitellogenesis and brooding, whereas males perform expensive courtship behaviors. We evaluated in a large-scale study the reproduction cost of females and males of Leptuca uruguayensis in a temperate estuary, where their reproductive efforts are synchronized in a short reproductive season. The reproductive investments (vitellogenesis, spermatophore production, and male reproductive behaviors) were measured and related to the dynamics of storage and expenditure of energy reserves (glycogen, total lipids, and total protein) in the hepatopancreas, ovary, and muscle of the enlarged cheliped, throughout one annual cycle. Maximum energy storage occurred in winter, a period of low activity, whereas minimum energy storage occurred during the reproductive period, characterized by expensive activities. The glycogen reserves of the hepatopancreas decreased about 66% in females and 61% in males, suggesting high and similar physiological costs of reproduction between sexes, despite their different reproductive strategies to maximize their fitness.

Lessons on Evolution from the Study of Edaphic Specialization

Plants adapted to special soil types are ideal for investigating evolutionary processes, including maintenance of intraspecific variation, adaptation, reproductive isolation, ecotypic differentiation, and the tempo and mode of speciation. Common garden and reciprocal transplant approaches show that both local adaptation and phenotypic plasticity contribute to edaphic (soil-related) specialization. Edaphic specialists evolve rapidly and repeatedly in some lineages, offering opportunities to investigate parallel evolution, a process less commonly documented in plants than in animals. Adaptations to soil features are often under the control of major genes and they frequently have direct or indirect effects on genes that contribute to reproductive isolation. Both reduced competitiveness and greater susceptibility to herbivory have been documented among some edaphic specialists when grown in ‘normal’ soils, suggesting that a high physiological cost of tolerance may result in strong divergent selection across soil boundaries. Interactions with microbes, herbivores, and pollinators influence soil specialization either by directly enhancing tolerance to extremes in soil conditions or by reducing gene flow between divergent populations. Climate change may further restrict the distribution of edaphic specialists due to increased competition from other taxa or, expand their ranges, if preadaptations to drought or other abiotic stressors render them more competitive under a novel climate.

Floral Mass per Area and Water Maintenance Traits Are Correlated with Floral Longevity in Paphiopedilum (Orchidaceae).

Floral longevity (FL) determines the balance between pollination success and flower maintenance. While a longer floral duration enhances the ability of plants to attract pollinators, it can be detrimental if it negatively affects overall plant fitness. Longer-lived leaves display a positive correlation with their dry mass per unit area, which influences leaf construction costs and physiological functions. However, little is known about the association among FL and floral dry mass per unit area (FMA) and water maintenance traits. We investigated whether increased FL might incur similar costs. Our assessment of 11 species of Paphiopedilum (slipper orchids) considered the impact of FMA and flower water-maintenance characteristics on FL. We found a positive relationship between FL and FMA. Floral longevity showed significant correlations with osmotic potential at the turgor loss and bulk modulus of elasticity but not with FA. Neither the size nor the mass per area was correlated between leaves and flowers, indicating that flower and leaf economic traits evolved independently. Therefore, our findings demonstrate a clear relationship between FL and the capacity to maintain water status in the flower. These economic constraints also indicate that extending the flower life span can have a high physiological cost in Paphiopedilum.

Divergence in physiological factors affecting swimming performance between anadromous and resident populations of brook charr Salvelinus fontinalis.

In this study, an anadromous strain (L) and a freshwater-resident (R) strain of brook charr Salvelinus fontinalis as well as their reciprocal hybrids, were reared in a common environment and submitted to swimming tests combined with salinity challenges. The critical swimming speeds (Ucrit ) of the different crosses were measured in both fresh (FW) and salt water (SW) and the variations in several physiological traits (osmotic, energetic and metabolic capacities) that are predicted to influence swimming performance were documented. Anadromous and resident fish reached the same Ucrit in both FW and SW, with Ucrit being 14% lower in SW compared with FW. The strains, however, seemed to use different underlying strategies: the anadromous strain relied on its streamlined body shape and higher osmoregulatory capacity, while the resident strain had greater citrate synthase (FW) and lactate dehydrogenase (FW, SW) capacity and either greater initial stores or more efficient use of liver (FW, SW) and muscle (FW) glycogen during exercise. Compared with R♀ L♂ hybrids, L♀ R♂ hybrids had a 20% lower swimming speed, which was associated with a 24% smaller cardio-somatic index and higher physiological costs. Thus swimming performance depends on cross direction (i.e. which parental line was used as dam or sire). The study thus suggests that divergent physiological factors between anadromous and resident S. fontinalis may result in similar swimming capacities that are adapted to their respective lifestyles.

The specificity of function of afferent and associative cortico-subcortical mechanisms in groups of healthy people and patients with epilepsy with different effectiveness of purposeful activity

The results of study of parameters of exogenous and cognitive evoked potential in groups of 72 healthy people and 148 patients with epilepsy and its influences on modeling purposeful activity (test Gorbov-Shulte) are presented. The interactions of mechanisms and prognostic value of physiologic parameters for determination of effectiveness of purposeful activity were estimated using artificial neural network technology. The higher physiological cost in activity of these mechanisms and greater role of characteristics of afferent systems activity in prognosis of resultness in patients with epilepsy are determined.

Is social dispersal stressful? A study in male crested macaques (Macaca nigra)

In gregarious species, dispersal events represent one of the most dramatic changes in social life and environment an animal will experience during life due to increased predation risk, aggression from unfamiliar conspecifics and the lack of social support. However, little is known about how individuals respond physiologically to dispersal and whether this process is stressful for the individuals involved. We therefore studied the physiological stress response during dispersal in the crested macaque, a primate species in which males often change groups. Over a period of 14months and 14 dispersal events in 4 groups, we determined faecal glucocorticoid metabolite (FGCM) levels during the process of immigration into a new group and examined a variety of factors (e.g. male age, rank achieved, number of males in the group) potentially affecting FGCM levels during this process. We found that FGCM levels were significantly elevated in the first few days upon immigration, after which levels returned quickly to baseline. FGCM response levels upon immigration were significantly and positively influenced by the number of males in the group. The rank a male achieved upon immigration, aggression received, as well as the proximity to other males did not significantly influence FGCM levels. Our data confirm previous findings on other species demonstrating that in crested macaques immigration into a new social group is associated with an acute endocrine stress response. However, given that stress hormone levels remained elevated only for a short period of time, we do not expect males to experience high physiological costs during immigration. Given our limited knowledge on the physiological responses to dispersal in animals, this study contributes to our understanding of dispersal more generally, and particularly inter-individual differences in the stress response and the potential physiological costs associated with these.

Transcriptome-Wide Differential Gene Expression in Bicyclus anynana Butterflies: Female Vision-Related Genes Are More Plastic.

Vision is energetically costly to maintain. Consequently, over time many cave-adapted species downregulate the expression of vision genes or even lose their eyes and associated eye genes entirely. Alternatively, organisms that live in fluctuating environments, with different requirements for vision at different times, may evolve phenotypic plasticity for expression of vision genes. Here, we use a global transcriptomic and candidate gene approach to compare gene expression in the heads of a polyphenic butterfly. Bicyclus anynana have two seasonal forms that display sexual dimorphism and plasticity in eye morphology, and female-specific plasticity in opsin gene expression. Nonchoosy dry season females downregulate opsin expression, consistent with the high physiological cost of vision. To identify other genes associated with sexually dimorphic and seasonally plastic differences in vision, we analyzed RNA-sequencing data from whole head tissues. We identified two eye development genes (klarsicht and warts homologs) and an eye pigment biosynthesis gene (henna) differentially expressed between seasonal forms. By comparing sex-specific expression across seasonal forms, we found that klarsicht, warts, henna, and another eye development gene (domeless) were plastic in a female-specific manner. In a male-only analysis, white (w) was differentially expressed between seasonal forms. Reverse transcription polymerase chain reaction confirmed that warts and white are expressed in eyes only, whereas klarsicht, henna and domeless are expressed in both eyes and brain. We find that differential expression of eye development and eye pigment genes is associated with divergent eye phenotypes in B. anynana seasonal forms, and that there is a larger effect of season on female vision-related genes.

Environmental tolerances of rare and common mangroves along light and salinity gradients.

Although mangroves possess a variety of morphological and physiological adaptations for life in a stressful habitat, interspecific differences in survival and growth under different environmental conditions can shape their local and geographic distributions. Soil salinity and light are known to affect mangrove performance, often in an interactive fashion. It has also been hypothesized that mangroves are intrinsically shade intolerant due to the high physiological cost of coping with saline flooded soils. To evaluate the relationship between stress tolerance and species distributions, we compared responses of seedlings of three widespread mangrove species and one narrow endemic mangrove species in a factorial array of light levels and soil salinities in an outdoor laboratory experiment. The more narrowly distributed species was expected to exhibit a lower tolerance of potentially stressful conditions. Two of the widespread species, Avicennia germinans and Lumnitzera racemosa, survived and grew well at low-medium salinity, regardless of light level, but performed poorly at high salinity, particularly under high light. The third widespread species, Rhizophora mangle, responded less to variation in light and salinity. However, at high salinity, its relative growth rate was low at every light level and none of these plants flushed leaves. As predicted, the rare species, Pelliciera rhizophorae, was the most sensitive to environmental stressors, suffering especially high mortality and reduced growth and quantum yield under the combined conditions of high light and medium-high salinity. That it only thrives under shaded conditions represents an important exception to the prevailing belief that halophytes are intrinsically constrained to be shade intolerant.

ENSO, nest predation risk, food abundance, and male status fail to explain annual variations in the apparent survival rate of a migratory songbird.

Adult mortality can be a major driver of population decline in species whose productivity is relatively low. Yet, little is known about the factors influencing adult survival rates in migratory bird species, nor do we know much about the longer-term effects of habitat disturbance on the fitness of individuals. The Ovenbird (Seiurus aurocapilla) is one of the vertebrate species most sensitive to forest management, yet it is still common and widespread. We monitored the fate of 330 colour-banded Ovenbird males in four pairs of 25-ha plots during 9 successive breeding seasons. One plot of each pair was treated through selection harvesting (30–40% basal area removed) during the first winter. We tested the following hypotheses: (1) higher physiological costs in harvested plots as a result of lower food abundance will reduce apparent survival rate (ASR) relative to controls; (2) lower ASR following years with low nest survival and higher probability of renesting; (3) fluctuations in ASR reflecting El Niño Southern Oscillation (ENSO); and (4) higher ASR in returning males than in recruits (unbanded immigrants) owing to greater site familiarity in the former. We tested the relative importance of these hypotheses, or combinations thereof, by generating 23 models explaining variation in ASR. The year-dependent model received the most support, showing a 41% decrease in ASR from 2007 to 2014. The important year-to-year variation we observed in ASR (Σwi = 0.99) was not explained by variation in nest predation risk nor by ENSO. There was also little evidence for an effect of selection harvesting on ASR of Ovenbird males, despite a slight reduction in lifespan relative to males from control plots (2.7 vs 2.9 years). An avenue worth exploring to explain this intriguing pattern would be to determine whether conditions at migratory stopover sites or in the wintering area of our focal population have gradually worsened over the past decade.

Heightened aggression and winning contests increase corticosterone but decrease testosterone in male Australian water dragons

Water dragons (Intellegama [Physignathus] lesueurii) are large (to >1m) agamid lizards from eastern Australia. Males are fiercely combative; holding a territory requires incessant displays and aggression against other males. If a dominant male is absent, injured or fatigued, another male soon takes over his territory. Our sampling of blood from free-ranging adult males showed that baseline levels of both testosterone and corticosterone were not related to a male’s social tactic (territorial versus non-territorial), or his frequency of advertisement display, aggression, or courtship behavior. Even when we elicited intense aggression by non-territorial males (by temporarily removing territory owners), testosterone did not increase with the higher levels of aggression that ensued. Indeed, testosterone levels decreased in males that won contests. In contrast, male corticosterone levels increased with the heightened aggression during unsettled conditions, and were higher in males that won contests. High chronic male–male competition in this dense population may favor high testosterone levels in all adult males to facilitate advertisement and patrol activities required for territory maintenance (by dominant animals), and to maintain readiness for territory take-overs (in non-territorial animals). Corticosterone levels increased in response to intense aggression during socially unstable conditions, and were higher in contest winners than losers. A positive correlation between the two hormones during socially unstable conditions suggests that the high stress of contests decreased androgen production. The persistent intense competition in this population appears to exact a high physiological cost, which together with our observation that males sometimes lose their territories to challengers may indicate cycling between these two tactics to manage long-term energetic costs.

Ketocarotenoid circulation, but not retinal carotenoid accumulation, is linked to eye disease status in a wild songbird

Pathogenic or parasitic infections pose numerous physiological challenges to organisms. Carotenoid pigments have often been used as biomarkers of disease state and impact because they integrate multiple aspects of an individual’s condition and nutritional and health state. Some diseases are known to influence carotenoid uptake from food (e.g. coccidiosis) and carotenoid use (e.g. as antioxidants/immunostimulants in the body, or for sexually attractive coloration), but there is relatively little information in animals about how different types of carotenoids from different tissue sources may be affected by disease. Here we tracked carotenoid accumulation in two body pools (retina and plasma) as a function of disease state in free-ranging house finches (Haemorhous mexicanus). House finches in eastern North America can contract mycoplasmal conjunctivitis (Mycoplasma gallisepticum, or MG), which can progress from eye swelling to eye closure and death. Previous work showed that systemic immune challenges in house finches lower carotenoid levels in retina, where they act as photoprotectors and visual filters. We assessed carotenoid levels during the molt period, a time of year when finches uniquely metabolize ketocarotenoids (e.g. 3-hydroxy-echinenone) for acquisition of sexually selected red plumage coloration, and found that males infected with MG circulated significantly lower levels of 3-hydroxy-echinenone, but no other plasma carotenoid types, than birds exhibiting no MG symptoms. This result uncovers a key biochemical mechanism for the documented detrimental effect of MG on plumage redness in H. mexicanus. In contrast, we failed to find a relationship between MG infection status and retinal carotenoid concentrations. Thus, we reveal differential effects of an infectious eye disease on carotenoid types and tissue pools in a wild songbird. At least compared to retinal sources (which appear somewhat more temporally stable than other body carotenoid pools, even to diseases of the eye evidently), our results point to either a high physiological cost of ketocarotenoid synthesis (as is argued in models of sexually selected carotenoid coloration) or high benefit of using this ketocarotenoid to combat infection.