Individual quality and carotenoid‐based plumage ornaments in male red bishops (Euplectes orix): plumage is not all that counts

Males in many bird species develop elaborate carotenoid‐based plumage ornaments that play an important role as signals of individual quality in intra‐ or intersexual selection. In the present study, we investigated which of several factors related to male condition and health affect the brightness and coloration of the carotenoid‐based orange–red breeding plumage in males of the red bishop (Euplectes orix), a polygynous and sexually dimorphic weaverbird species. The study revealed a very complex pattern, with the relationships between plumage traits and both heterophil‐to‐lymphocyte ratio and blood parasite load varying considerably among seasons, suggesting a strong influence of environmental conditions. Furthermore, overall condition of males strongly affected the association pattern between plumage traits and other factors, with males in bad condition being forced to allocate resources away from plumage elaboration to body maintenance or the enhancement of immune functions, whereas males in good condition can afford to invest in plumage ornamentation without obvious detrimental effects on health. Thus, females cannot rely on plumage characteristics alone to gather information on male quality, but have to assess additional traits that advertise general male health status. Perhaps surprisingly, testosterone levels were not related to male plumage characteristics. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 384–397.     

Estimating age‐dependent survival when juveniles resemble females: Invasive ring‐necked parakeets as an example

Many species only show sexual dimorphism at the age of maturity, such that juveniles typically resemble females. Under these circumstances, estimating accurate age‐specific demographic parameters is challenging. Here, we propose a multievent model parameterization able to estimate age‐dependent survival using capture–recapture data with uncertainty in age and sex assignment of individuals. We illustrate this modeling approach with capture–recapture data from the ring‐necked parakeet Psittacula krameri. We analyzed capture, recapture, and resighting data (439 recaptures/resightings) of 156 ring‐necked parakeets tagged with neck collars in Barcelona city from 2003 to 2016 to estimate the juvenile and adult survival rate. Our models successfully estimated the survival probabilities of the different age classes considered. Survival probability was similar between adults (0.83, 95% CI = 0.77–0.87) and juveniles during their second (0.79, 95% CI = 0.58–0.87) and third winter (0.83, 95% CI = 0.65–0.88). The youngest juveniles (1st winter) showed a slightly lower survival (0.57, 95% CI = 0.37–0.79). Among adults, females showed a slightly higher survival than males (0.87, 95% CI = 0.78–0.93; and 0.80, 95% CI = 0.73–0.86, respectively). These high survival figures predict high population persistence in this species and urge management policies. The analysis also stresses the usefulness of multievent models to estimate juvenile survival when age cannot be fully ascertained.     

Adult dietary protein has age‐ and context‐dependent effects on male post‐copulatory performance

The highly conserved effect of dietary protein restriction on lifespan and ageing is observed in both sexes and across a vast range of taxa. This extension of lifespan is frequently accompanied by a reduction in female fecundity, and it has been hypothesized that individuals may reallocate resources away from reproduction and into somatic maintenance. However, effects of dietary protein restriction on male reproduction are less consistent, suggesting that these effects may depend on other environmental parameters. Using the neriid fly, Telostylinus angusticollis, we examined age‐specific effects of adult dietary protein restriction on male post‐copulatory reproductive performance (fecundity and offspring viability). To explore the context dependence of these effects, we simultaneously manipulated male larval diet and adult mating history. We found that protein‐restricted males sired less viable offspring at young ages, but offspring viability increased with paternal age and eventually exceeded that of fully fed males. The number of eggs laid by females was not affected by male dietary protein, whereas egg hatching success was subject to a complex interaction of male adult diet, age, larval diet and mating history. These findings suggest that effects of protein restriction on male reproduction are highly context dependent and cannot be explained by a simple reallocation of resources from reproduction to somatic maintenance. Rather, these effects appear to involve changes in the scheduling of male reproductive investment with age.     

Dexamethasone treatment supports age‐related maturation of the stress response in altricial nestling birds

In birds, the magnitude of the adrenocortical stress response can be down‐regulated during specific life‐history stages. Such modulation likely occurs when the effects of mounting robust corticosterone (Cort) elevations interfere with the normal progression of critical lifecycle activities (e.g. development, molt, migration, reproduction). The developmental hypothesis posits that altricial birds should display a ‘stress hyporesponsive period’ during the early post‐natal life stages, characterized by reduced adrenocortical stress responses compared to adult birds and a gradual age‐related increase. Such modulation would allow avoiding the potential deleterious effects that long‐term elevations of circulating Cort might exert on growth and development, when the physiological and behavioral abilities to cope with disturbance are limited. Two proximate hypotheses have been proposed to explain this age‐dependent pattern of Cort secretion. The ‘maturation hypothesis’ proposes a progressive age‐related growth, maturation and enhanced sensitivity to sensory input of the Hypothalamic‐Pituitary‐Adrenal (HPA) axis tissues, whereas the ‘negative feedback attenuation hypothesis’ proposes a gradual attenuation in the intensity of the negative feedback in the HPA axis. Here we tested these hypotheses by experimentally inducing negative feedback on the HPA axis via dexamethasone (DEX) treatment in nestling white storks Ciconia ciconia. Nestling age positively affected stress‐induced plasma Cort (STRESS‐Cort) levels during experimental handling and restraint, thus supporting the developmental hypothesis. DEX treatment significantly reduced STRESS‐Cort levels compared to saline (SAL) treatment, thus eliciting the expected negative feedback on the HPA axis. However, inter‐ and intra‐individual comparisons indicated no age effects on the intensity of the negative feedback exerted by DEX. Our results do not support the negative feedback attenuation hypothesis and suggest that progressive maturation of the HPA axis tissues is the proximate mechanism responsible for age‐related changes in the stress response during avian post‐natal development. We encourage further tests of the proposed proximate mechanisms during migration, breeding and molt.     

Delayed plumage maturation in green‐backed flycatchers (Ficedula elisae): An evidence of female mimicry

Delayed plumage maturation (DPM) is the delayed acquisition of an adult color and pattern of plumage until after the first potential breeding period. Among the hypotheses proposed to explain DPM, the female mimicry hypothesis (FMH) has received considerable attention. FMH predicts that after‐second‐calendar‐year (ASY) males should attack ASY males more than second‐calendar‐year (SY) males and females, while no difference between the two latter. Few studies have been thought as support for FMH, while in fact most of them give no conclusive evidence to the assumption of FMH that ASY males are unable to distinguish SY males from females. Thus, other support besides behavioral experiments, such as it is physiologically impossible to discriminate SY males and females from avian perspective, is important in testing FMH. We studied color differences in six plumage patches between ASY male, SY male and female by analyzing reflectance spectra in the avian visual system, and tested the prediction of FMH by conducting intrusion experiments on territorial males with three kinds of conspecifics (i.e., ASY males, SY males and females) as territory “intruders” in the green‐backed flycatcher (Ficedula elisae). It is physiologically impossible for ASY males to distinguish SY males and females through the plumage color of crown, mantle, rump, and throat patches, moreover difficult to distinguish through breast and belly patches even under reasonable viewing conditions. ASY males were more aggressive toward ASY males than SY males and females with no differences between the two latter. SY males showed a slightly but not significantly higher attack intensity on ASY males than SY males and females. Our results suggest that female mimicry is more likely to be the explanation for DPM in the green‐backed flycatcher. To our knowledge, this is the first study combining avian visual system and behavioral experiments in testing hypotheses of DPM.     

Ultraviolet plumage does not signal social status in free-living blue tits; an experimental test

Ultraviolet (UV) signals are suggested to be sexually selectedin a wide range of taxa. Most research, however, has focusedon the role of UV signals in mate choice, whereas possible functionsin intraspecific competition remain largely untested. Studieson other colors indicate that ornaments preferred by femalescan also function as signals of social status in competitiveinteractions between individuals. Whereas these colors are mainlypigment based, UV reflectance is generally caused by selectivereflectance of light from surface structures. Here we test experimentallywhether the structurally based UV-reflective crown plumage inthe blue tit (Cyanistes caeruleus) serves as a signal of statusin interindividual competition. We reduced the crown UV reflectanceof free-living blue tits in winter and compared their probabilityof winning conflicts over food at a feeding table with control-treatedand untreated individuals. Although we controlled for effectsof sex, age, and distance from territory, we found no effectof reduced UV reflectance on the probability of winning norwere conflicts involving UV-reduced individuals more likelyto escalate. Therefore, we conclude that the UV reflectanceof the blue tit's crown does not serve as a signal of statusin competition over food in winter. We suggest that the observedsite-dependent dominance structure may constrain the opportunityfor a status signal to evolve and that enhancing attractivenessin mate choice may be the sole function of the crown's UV reflectance.     

Maternal care,mother–offspring aggregation and age‐dependent coadaptation in the European earwig

Benefits and costs of parental care are expected to change with offspring development and lead to age‐dependent coadaptation expressed as phenotypic (behavioural) matches between offspring age and parental reproductive stage. Parents and offspring interact repeatedly over time for the provision of parental care. Their behaviours should be accordingly adjusted to each other dynamically and adaptively, and the phenotypic match between offspring age and parental stage should stabilize the repeated behavioural interactions. In the European earwig (Forficula auricularia), maternal care is beneficial for offspring survival, but not vital, allowing us to investigate the extent to which the stability of mother–offspring aggregation is shaped by age‐dependent coadaptation. In this study, we experimentally cross‐fostered nymphs of different age classes (younger or older) between females in early or late reproductive stage to disrupt age‐dependent coadaptation, thereby generating female–nymph dyads that were phenotypically matched or mismatched. The results revealed a higher stability in aggregation during the first larval instar when care is most intense, a steeper decline in aggregation tendency over developmental time and a reduced developmental rate in matched compared with mismatched families. Furthermore, nymph survival was positively correlated with female–nymph aggregation stability during the early stages when maternal care is most prevalent. These results support the hypothesis that age‐related phenotypically plastic coadaptation affects family dynamics and offspring developmental rate.     

Production of male flowers does not decrease with plant size in insect‐pollinated Sagittaria trifolia,contrary to predictions of size‐dependent sex allocation

Abstract It has been proposed that relative allocation to female function increases with plant size in animal‐pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size‐dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect‐pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high‐density population, 48% of ramets were male without female flowers, but in the low‐density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal‐pollinated plants, pointing towards further studies to test the hypothesis of size‐dependent sex allocation using different allocation currencies.     

Frequency‐dependent two‐sex models: a new approach to sex ratio evolution with multiple maternal conditions

Mothers that experience different individual or environmental conditions may produce different proportions of male to female offspring. The Trivers‐Willard hypothesis, for instance, suggests that mothers with different qualities (size, health, etc.) will use different sex ratios if maternal quality differentially affects sex‐specific reproductive success. Condition‐dependent, or facultative, sex ratio strategies like these allow multiple sex ratios to coexist within a population. They also create complex population structure due to the presence of multiple maternal conditions. As a result, modeling facultative sex ratio evolution requires not only sex ratio strategies with multiple components, but also two‐sex population models with explicit stage structure. To this end, we combine nonlinear, frequency‐dependent matrix models and multidimensional adaptive dynamics to create a new framework for studying sex ratio evolution. We illustrate the applications of this framework with two case studies where the sex ratios depend one of two possible maternal conditions (age or quality). In these cases, we identify evolutionarily singular sex ratio strategies, find instances where one maternal condition produces exclusively male or female offspring, and show that sex ratio biases depend on the relative reproductive value ratios for each sex.     

Faithful females receive more help: the extent of male parental care during incubation in relation to extra‐pair paternity in songbirds

Parental care provided by males occurs in a diverse array of animals and there are large differences among species in its extent compared with female care. However, social and ecological factors responsible for interspecific differences in male's share of parental duties remain unclear. Genetic fidelity of females has been long considered important. Theory predicts that females should receive more help from their mates in raising the offspring in species with high genetic fidelity. Using avian incubation behaviour as a model system, we confirmed this prediction. The extent of male's help during incubation increased with decreasing rate of extra‐pair paternity across species (22 species of socially monogamous songbirds from 13 families; male's share of incubation ranged from 6% to 58%), even after accounting for covariates, biases in species selection and intraspecific variability. Moreover, this result was not sensitive to two different phylogenies and branch length estimates. We suggest that our findings support the notion, backed by theory, that genetic fidelity is an important factor in the evolution of male parental care. We offer several behavioural scenarios for the coevolution between male's share of parental duties and the genetic mating system.     

Males are cheaper,or the extreme consequence of size/age‐dependent sex allocation: sexist gender diphasy in Fritillaria montana (Liliaceae)

The bulbous geophyte Fritillaria montana is partially self‐compatible and capable of switching gender. Small flowering plants produce only single male flowers, but larger plants produce hermaphrodite or, rarely, male and hermaphrodite flowers. Eight populations in peninsular Italy were sampled to determine the frequency and size distributions of male and hermaphrodite plants, and to determine the relationship of plant size to male and hermaphrodite flower production. Male plants were significantly smaller than hermaphrodites and made up 14.5–47.8% (100% in one small population) of flowering plants within populations. There were no significant differences in male fitness among female‐sterile and hermaphrodite flowers, as they both possessed full and comparable fertilizing power. Therefore, the gender variation observed in F. montana is likely to depend on resource‐dependent sex allocation. From an evolutionary perspective, we highlight the occurrence of similar mechanisms of gender variation in other representatives of the order Liliales. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 323–333.     

Modeling and quantifying frequency‐dependent fitness in microbial populations with cross‐feeding interactions

Coexistence of two or more populations by frequency‐dependent selection is common in nature, and it often arises even in well‐mixed experiments with microbes. If ecology is to be incorporated into models of population genetics, then it is important to represent accurately the functional form of frequency‐dependent interactions. However, measuring this functional form is problematic for traditional fitness assays, which assume a constant fitness difference between competitors over the course of an assay. Here, we present a theoretical framework for measuring the functional form of frequency‐dependent fitness by accounting for changes in abundance and relative fitness during a competition assay. Using two examples of ecological coexistence that arose in a long‐term evolution experiment with Escherichia coli, we illustrate accurate quantification of the functional form of frequency‐dependent relative fitness. Using a Monod‐type model of growth dynamics, we show that two ecotypes in a typical cross‐feeding interaction—such as when one bacterial population uses a byproduct generated by another—yields relative fitness that is linear with relative frequency.     

Density‐dependent survival varies with species life‐history strategy in a tropical forest

Species coexistence in diverse communities likely results from multiple interacting factors. Mechanisms such as conspecific negative density dependence (CNDD) and varying life‐history strategies related to resource partitioning are known to influence plant fitness, and thereby community composition and diversity. However, we have little understanding of how these mechanisms interact and how they vary across life stages. Here, we document the interaction between CNDD and life‐history strategy, based on growth‐mortality trade‐offs, from seedling to adult tree for 47 species in a tropical forest. Species’ life‐history strategies remained consistent across stages: fast‐growing species had higher mortality than slow‐growing species at all stages. In contrast, mean CNDD was strongest at early life stages (i.e. seedling, sapling). Fast‐growing species tended to suffer greater CNDD than slow‐growing species at several, but not all life stages. Overall, our results demonstrate that coexistence mechanisms interact across multiple life stages to shape diverse tree communities.     

Density‐dependent fitness,not dispersal movements,drives temporal variation in spatial genetic structure in dark‐eyed juncos (Junco hyemalis)

Some studies have found that dispersal rates and distances increase with density, indicating that density‐dependent dispersal likely affects spatial genetic structure. In an 11‐year mark–recapture study on a passerine, the dark‐eyed junco, we tested whether density affected dispersal distance and/or fine‐scale spatial genetic structure. Contrary to expectations, we found no effect of predispersal density on dispersal distance or the proportion of locally produced juveniles returning to the population from which they hatched. However, even though density did not affect dispersal distance or natal return rates, we found that density still did affect spatial genetic structure. We found significant positive spatial genetic structure at low densities of (postdispersal) adults but not at high densities. In years with high postdispersal (adult) densities that also had high predispersal (juvenile) densities in the previous year, we found negative spatial genetic structure, indicating high levels of dispersal. We found that density also affected fitness of recruits, and fitness of immigrants, potentially linking these population parameters with the spatial genetic structure detected. Immigrants and recruits rarely nested in low postdispersal density years. In contrast, in years with high postdispersal density, recruits were common and immigrants had equal success to local birds, so novel genotypes diluted the gene pool and effectively eliminated positive spatial genetic structure. In relation to fine‐scale spatial genetic structure, fitness of immigrants and new recruits is poorly understood compared to dispersal movements, but we conclude that it can have implications for the spatial distribution of genotypes in populations.     

Dietary flavonoids enhance conspicuousness of a melanin‐based trait in male blackcaps but not of the female homologous trait or of sexually monochromatic traits

Signalling theory predicts that signals should fulfil three fundamental requirements: high detectability, discriminability and, most importantly, reliability. Melanins are the most common pigments in animals. Correlations between genotypic and phenotypic qualities of the sender and size and morph of melanin‐based traits are known, but it is contentious whether melanin‐based colouration may signal any quality. We examined the effect of supplementing blackcaps (Sylvia atricapilla) with flavonoids, potent plant antioxidants, on plumage colouration. We demonstrate that melanin‐based colour can fulfil all requirements of signals of phenotypic condition. As predicted by sexual selection theory, flavonoid supplementation influenced only the sexually dichromatic black cap of males, whereas the female homologous trait and the sexually monochromatic back colouration remained unaffected. Using avian vision models we show that birds can estimate male flavonoid intake from colouration of males’ black cap. Because flavonoid ingestion can increase immune responsiveness in blackcaps, melanin head colouration may signal environmentally determined immune condition.     

Melanocortin‐1‐receptor (MC1R) variation is not associated with parasite burden in a neotropical bird,the bananaquit (Coereba flaveola)

It has been suggested that selection on melanocortin‐1‐receptor (MC1R) polymorphism, a common cause of melanic colour variation in vertebrates, results from pleiotropic effects of the gene in the immune system. Here we present the first test of whether MC1R variation is associated with differences in parasite abundance in a natural population. Bananaquits (Coereba flaveola) (Linnaeus, 1758) living on Grenada in the Caribbean exhibit a melanic plumage dimorphism as a result of a mutation in MC1R. The proportion of black individuals increases clinally towards the central, wetter parts of the island. We captured bananaquits through the cline and quantified parasite abundances. Avian malaria, feather mites, and mallophaga lice varied significantly in abundance across the cline; however, neither these infections, nor coccidia, nor arboviruses showed overall differences between the morphs. Feather mites tended to be more abundant on black individuals, in areas where the black morph was more common. This may result from differences in microhabitat use by the two morphs. These patterns do not support the idea that MC1R variation in itself results in differing susceptibility to parasites. © 2013 The Linnean Society of London     

Treatment with IFN‐γ prevents insulin‐dependent PKB,p70S6k phosphorylation and protein synthesis in mouse C2C12 myogenic cells

The purpose of the present study was to examine the potential effect of IFN‐γ (interferon‐γ) on the cellular content and phosphorylation of PKB (protein kinase B), p70^S6k (p70 S6 kinase) and MAPK (mitogen‐activated protein kinase), and on the ability of insulin to stimulate the glucose uptake and protein synthesis in mouse C2C12 myotubes. Insulin (100 nmol/l) stimulated glucose uptake in C2C12 myotubes by 203.4%. Glucose uptake in cells differentiated in the presence of IFN‐γ (10 ng/ml) was increased by 165.8% and was not further significantly modified by the addition of insulin (183.4% of control value). Insulin increased the rate of protein synthesis by 198.8%. The basal rate of protein synthesis was not affected by IFN‐γ; however, this cytokine abolished the insulin effect. Cellular levels of PKB, p70^S6k, p42^MAPK and p44^MAPK were not modified by IFN‐γ. Insulin caused the phosphorylation of PKB and the activation of p70^S6k, but not p42^MAPK and p44^MAPK. In cells differentiated in the presence of IFN‐γ, the insulin‐mediated PKB phosphorylation was significantly diminished, whereas the phosphorylation of p70^S6k was completely prevented. Pretreatment of C2C12 myogenic cells with IFN‐γ led to the marked increase in p42^MAPK phosphorylation. Exposure of C2C12 myoblasts to IFN‐γ impaired MyoD and myogenin expression and decreased the fusion index on the fifth day of differentiation. In conclusion, (i) IFN‐γ present in the extracellular environment during C2C12 myoblast differentiation prevents the stimulatory action of insulin on protein synthesis; (ii) IFN‐γ‐induced insulin resistance of protein synthesis in myogenic cells can be associated with the decreased phosphorylation of PKB and p70^S6k, as well as with the augmented basal phosphorylation of p42^MAPK; (iii) this cytokine effect can be partly explained by alterations in the differentiation process.