Hypothalamic gene switches control transitions between seasonal life history states in a night-migratory photoperiodic songbird

This study investigated photoperiodic plasticity in hypothalamic expression of genes implicated in the photoperiodic light perception (rhodopsin, melanopsin, neuropsin and peropsin), transduction (pax6, bmal1, clock, per2 and casr), induction (eya3, tshβ, dio2 and dio3, gnrh and gnih) and metabolism (NPY, sirtuin1, foxO1, hmgcr, citrate synthase and dehydrogenases) in photosensitive and photorefractory redheaded buntings. There was a significant increase in eya3, tsh β, dio2, pax6 and rhodopsin and decrease in dio3 mRNA expression at hour 15 and/or 19 on the day photosensitive buntings were subjected to a 13- or 16 h, but not to 8- and 11 h light exposure. Downstream reproductive and metabolic gene expression was not altered, except for an increase in those genes coding for succinate and malate dehydrogenase enzymes involved in lipogenesis. Photorefractory buntings had high dio3 mRNA expression which significantly declined after 1 short day exposure, suggesting possible involvement of dio3 in the maintenance of photorefractoriness. Positive correlation of rhodopsin on eya 3 and tshβ indicates its role in photoperiodic timing, perhaps involving the peropsin and pax6 genes. These results suggest that rapid switching of hypothalamic gene expression underlies photoperiod-induced seasonal plasticity and regulates transitions from photosensitive to photostimulated and from photorefractory to photosensitive states in migratory songbirds.

The impact of increased food availability on reproduction in a long-distance migratory songbird: implications for environmental change?

Many populations of migratory songbirds are declining or shifting in distribution. This is likely due to environmental changes that alter factors such as food availability that may have an impact on survival and/or breeding success. We tested the impact of experimentally supplemented food on the breeding success over three years of northern wheatears (Oenanthe oenanthe), a species in decline over much of Europe. The number of offspring fledged over the season was higher for food-supplemented birds than for control birds. The mechanisms for this effect were that food supplementation advanced breeding date, which, together with increased resources, allowed further breeding attempts. While food supplementation did not increase the clutch size, hatching success or number of chicks fledged per breeding attempt, it did increase chick size in one year of the study. The increased breeding success was greater for males than females; males could attempt to rear simultaneous broods with multiple females as well as attempting second broods, whereas females could only increase their breeding effort via second broods. Multiple brooding is rare in the study population, but this study demonstrates the potential for changes in food availability to affect wheatear breeding productivity, primarily via phenotypic flexibility in the number of breeding attempts. Our results have implications for our understanding of how wheatears may respond to natural changes in food availability due to climate changes or changes in habitat management.

Continuous variation rather than specialization in the egg phenotypes of cuckoos (Cuculus canorus) parasitizing two sympatric reed warbler species

The evolution of brood parasitism has long attracted considerable attention among behavioural ecologists, especially in the common cuckoo system. Common cuckoos (Cuculus canorus) are obligatory brood parasites, laying eggs in nests of passerines and specializing on specific host species. Specialized races of cuckoos are genetically distinct. Often in a given area, cuckoos encounter multiple hosts showing substantial variation in egg morphology. Exploiting different hosts should lead to egg-phenotype specialization in cuckoos to match egg phenotypes of the hosts. Here we test this assumption using a wild population of two sympatrically occurring host species: the great reed warbler (Acrocephalus arundinaceus) and reed warbler (A. scirpaceus). Using colour spectrophotometry, egg shell dynamometry and egg size measurements, we studied egg morphologies of cuckoos parasitizing these two hosts. In spite of observing clear differences between host egg phenotypes, we found no clear differences in cuckoo egg morphologies. Interestingly, although chromatically cuckoo eggs were more similar to reed warbler eggs, after taking into account achromatic differences, cuckoo eggs seemed to be equally similar to both host species. We hypothesize that such pattern may represent an initial stage of an averaging strategy of cuckoos, that – instead of specializing for specific hosts or exploiting only one host – adapt to multiple hosts.

Mercury exposure of a wetland songbird, Agelaius phoeniceus, in the New York metropolitan area and its effect on nestling growth rate

The potential for mercury accumulation in free-living passerine birds is now recognized to be much greater than previously assumed. However, lowest observable effect levels have yet to be well established for this taxonomic group and it is usually unknown whether levels observed in the wild are causing adverse effects. We measured total blood mercury (THg) levels and took repeated morphological measurements from nestling red-winged blackbirds (Agelaius phoeniceus; N = 39) in the New York metropolitan area to investigate whether mercury affected their growth rate. We also compared THg levels of nestlings (and parents; N = 14) between our two study sites, which included riparian habitats along a city river and surrounding ponds in a nearby suburb, to examine differences between birds within and beyond the urban core. THg levels ranged 0.009-0.284 ppm in nestlings and 0.036-0.746 ppm in adults. Adults and nestlings had significantly higher THg outside of the city than within, possibly due to the ability of rivers to flush contaminants and the higher methylation potential of ponds. Among our candidate sets, models containing THg had minimal support for explaining variation in nestling growth rate. Summed Akaike weights further showed that THg had little relative importance. Mercury pollution in our sites may be low, or feather growth may have been sufficient to protect nestlings from accumulating harmful mercury levels in living tissues.

Pathways and consequences of contaminant flux to Acadian flycatchers (Empidonax virescens) in urbanizing landscapes of Ohio, USA

A prevalent environmental contaminant, mercury (Hg) is mobile and persistent in aquatic systems, where it often occurs in its bioavailable form methylmercury. Because methylmercury can bioaccumulate in aquatic insects and then transfer to terrestrial food webs, riparian consumers reliant upon aquatic emergent insects, should be disproportionately affected. Using the aerial insectivore Acadian flycatcher (Empidonax virescens) as a focal species, we examined (1) the extent to which total Hg loads in breeding flycatchers affected body condition and reproductive output and (2) potential pathways of contaminant flux in 19 riparian forest fragments distributed across an urban-to-rural landscape gradient in Ohio, USA. From April-August 2011-2012, we collected blood samples from adult (n=76) and nestling (n=17 from 7 nests) flycatchers, monitored their annual reproductive success (i.e., total number of fledglings), and sampled water, sediment, and aquatic emergent insects at each site. Hg concentrations in adult flycatcher blood (47 to 584 μg/kg, x¯=211.8, SD=95.5) were low relative to published advisory levels and not related to body condition. However, even at low concentrations, blood Hg was negatively related to reproductive success, with a 0.83 decline in the number of fledglings per μg/kg (loge) increase of blood Hg. Adult flycatchers had 11× greater concentrations of blood Hg than their offspring. Hg levels in flycatcher blood were not predicted by Hg concentrations in sediment, water, or aquatic emergent insects, with the exception of rural landscapes alone, in which flycatcher Hg was negatively related to sediment Hg. In addition to illustrating the difficulty of predicting exposure pathways that may vary among landscape contexts, our study provides evidence that even trace levels of contaminants may impair reproductive success of free-living songbirds.

Corticosterone exposure during development has sustained but not lifelong effects on body size and total and free corticosterone responses in the zebra finch

Animals exposed to stress during development experience sustained morphological, physiological, neurological, and behavioral consequences. For example, elevated glucocorticoids (GCs) during development can increase GC secretion in adults. Studies have examined the sustained effects of elevated developmental GCs on total GC responses, but no study to date has examined the effect of developmental stress on corticosteroid binding globulin (CBG). CBG is a protein which binds to GCs and facilitates their transportation in blood. When bound to CBG, GCs are unavailable to interact with target tissues. Exposure to stress can decrease CBG capacity and, thus, increase free GCs (the portion of unbound GCs). We examined the long-term effects of elevated corticosterone (CORT) during development (12-28days post-hatch) on acute stress responses, negative feedback, and CBG capacity at 30, 60, and 90days post-hatch in zebra finches. Additionally, we evaluated the effect of CORT treatment on body size and condition at 28, 60, and 90days post-hatch. CORT exposed birds had higher acute stress responses at 30days post-hatch compared to control birds. However, there was no treatment effect at 60 or 90days post-hatch. CBG levels were not affected by treatment, and so free CORT estimations reflected patterns in total CORT. CORT treatment decreased growth and condition in zebra finches at 28days post-hatch, but these differences were not present at later life history stages. However, brood size had a sustained effect on body size such that birds reared in medium sized broods were larger at 28, 60, and 90days post-hatch. These results demonstrate the complexity of early environmental effects on adult phenotype and suggest that some conditions may have stronger programmatic effects than others.

Toxic exposure of songbirds to lead in the Southeast Missouri Lead Mining District

Mining and smelting in the Southeast Missouri Lead Mining District has caused widespread contamination of soils with lead (Pb) and other metals. Soils from three study sites sampled in the district contained from approximately 1,000-3,200 mg Pb/kg. Analyses of earthworms [33-4,600 mg Pb/kg dry weight (dw)] collected in the district showed likely high Pb exposure of songbirds preying on soil organisms. Mean tissue Pb concentrations in songbirds collected from the contaminated sites were greater (p < 0.05) than those in songbirds from reference sites by factors of 8 in blood, 13 in liver, and 23 in kidney. Ranges of Pb concentrations in livers (mg Pb/kg dw) were as follows: northern cardinal (Cardinalis cardinalis) = 0.11-3.0 (reference) and 1.3-30 (contaminated) and American robin (Turdus migratorius) = 0.43-8.5 (reference) and 7.6-72 (contaminated). Of 34 adult and juvenile songbirds collected from contaminated sites, 11 (32%) had hepatic Pb concentrations that were consistent with adverse physiological effects, 3 (9%) with systemic toxic effects, and 4 (12%) with life-threatening toxic effects. Acid-fast renal intranuclear inclusion bodies, which are indicative of Pb poisoning, were detected in kidneys of two robins that had the greatest renal Pb concentrations (952 and 1,030 mg/kg dw). Mean activity of the enzyme delta-aminolevulinic acid dehydratase (ALAD) in red blood cells, a well-established bioindicator of Pb poisoning in birds, was decreased by 58-82% in songbirds from the mining sites. We conclude that habitats within the mining district with soil Pb concentrations of ≥1,000 mg Pb/kg are contaminated to the extent that they are exposing ground-feeding songbirds to toxic concentrations of Pb.

Avian feathers as bioindicators of the exposure to heavy metal contamination of food

The aim of this study was to determine the possibility of using feathers of blue tit nestlings to assess the level of endogenous accumulation of lead. For this purpose we conducted an experiment with lead application to randomly chosen nestlings from eight randomly drawn broods. Five days after the exposure, feathers of lead-treated nestlings had significantly higher lead concentrations than control nestlings. This result suggests that feathers can be used as reliable non-destructive bioindicators to assess the level of heavy metals originating from contaminated food, which is of great significance for comparative studies on ecological consequences of pollution.

Genome-brain-behavior interdependencies as a framework to understand hormone effects on learned behavior

Hormones have profound effects on the maturation and function of the zebra finch song system. Hormones often signal through receptors that directly or indirectly regulate transcription. In this way, hormones and the genome are functionally connected. Genome-brain-behavior interdependencies are often studied on evolutionary timescales but we can now apply and test these relationships on short timescales, relevant to an individual. Here, we begin to place patterns of hormone-related gene expression into the timeframe of an individual's lifespan to consider how hormones contribute to organization of neural systems necessary for learned behavior, and how they might signal during experience in ways that affect future behavior. This framework illustrates both how much investigations into genome and hormone function are intertwined, and how much we still need to learn.

Assessing heavy metal pollution using Great Tits (Parus major): feathers and excrements from nestlings and adults

Passerine species have been increasingly used as bioindicators of metal bioaccumulation especially by taking benefit of non-invasive procedures, such as collecting feathers and excrements. In 2009, metal (As, Cd, Cu, Hg, Ni, Pb, Se and Zn) concentrations were determined in feathers and excrements of nestling and adult female great tits (Parus major) in industrial (a paper mill) and rural sites in maritime pine forests on the west coast of Portugal. The aim of this study was to compare the levels of metals between the areas but also between sampling methods (feather vs. excrement) and age classes (nestling vs. adult). Although excrements and feathers of nestling great tits showed different concentrations, similar patterns of accumulation were detected in both study areas. There was a significantly higher concentration of mercury in the industrial area and significantly higher concentrations of arsenic in the rural area in both sample types. Metal levels in adult females had quite different results when compared to nestlings, and only nickel presented significantly higher levels near the paper mill. Since metal levels showed a consistent pattern in feathers and excrements of nestling great tits, we conclude that both represent good and non-invasive methods for the evaluation of these elements in polluted areas.

Oxidative status in nestlings of three small passerine species exposed to metal pollution

Antioxidant defense has an important role in the protection of organisms against oxidative stress caused by reactive oxygen species (ROS). Many metals are capable of generating ROS and inducing oxidative damage, and may therefore lead to changes in oxidative regulation. We studied species-specific variation in the oxidative status of great tit (Parus major), blue tit (Cyanistes caeruleus) and pied flycatcher (Ficedula hypoleuca) nestlings in a vicinity of a non-ferrous smelter. Non-enzymatic (glutathione [tGSH], GSH:GSSG ratio, and carotenoids) and enzymatic (glutathione peroxidase [GP], glutathione-S-transferase [GST], superoxide dismutase [SOD], and catalase [CAT]) antioxidants were evaluated to determine the effects of metal exposure on the oxidative status of the birds. We found strong evidence of interspecific variation in CAT and SOD activities, whereas less variation was observed in parameters related to glutathione metabolism. Oxidative state (in terms of tGSH and GSH:GSSG) did not vary between species, suggesting that different species may employ different antioxidant pathways to achieve the same oxidative state. Oxidative status was only weakly related to metal exposure, and these associations were further obscured by species-specific environmental effects. Our results indicate that effects on oxidative status observed in one species cannot be generalized to other ones. Future work should attempt to incorporate species-specific biology and environmental context into assessments of contaminant impacts on oxidative regulation of passerine birds.

Neonatal handling alters the development of the adrenocortical response to stress in a wild songbird (eastern bluebird, Sialia sialis)

Neonatal handling of captive vertebrates can shape the development of their hypothalamo-pituitary-adrenal (HPA) axis and alter their ability to respond to stressful stimuli later in life. However, the long-term effects of such handling on this endocrine axis in free-living species are not well understood. We investigated the effects of age and neonatal handling on corticosterone secretion in response to restraint in eastern bluebird (Sialia sialis) chicks. We found that unhandled ("naïve") and handled ("experienced") chicks exhibited no corticosterone response to handling early in development. Thereafter, naïve individuals exhibited the progressive development of a corticosterone response with age, and by day 12 post-hatch, the response resembled that of adult bluebirds. Experienced nestlings, which were handled every other day from the day of hatch, showed a similar pattern of HPA development until day 12 post-hatch, when their corticosterone response was significantly reduced compared to that of naïve nestlings. In contrast, chicks that were handled only once, when 10days old, did not show a reduced corticosterone response at 12days old. Taken together, our data suggest that a certain threshold of accumulated neonatal handling episodes is necessary to depress corticosterone secretion, and/or that the cumulative effects of several handling episodes only manifest themselves once the HPA axis is fully developed. Our findings, in concert with studies on two other wild species, indicate that routine handling of nestlings in the field can alter their responses to stress in a species-specific manner, potentially leading to important fitness consequences.

Testicular growth and regression are not correlated with Dio2 expression in a wild male songbird, sturnus vulgaris, exposed to natural changes in photoperiod

Timing of seasonal breeding in birds and mammals is regulated by changing the day length and is dependent on the presence of thyroid hormones. A mechanism for thyroid-dependent control of seasonality has been proposed, in which exposure to long day lengths induces rapid local conversion of T4 to its bioactive form, T3, via the up-regulation of the enzyme type 2 iodothyronine deiodinase (Dio2) in the brain, and the down-regulation of Dio3 (which inactivates T3). Such changes were correlated with gonadotropin release and gonadal growth in quail. This mechanism was elucidated in a domesticated species (quail) exposed to unnatural acute changes in day length. Here we investigated the Dio2/Dio3 mechanism in a wild species, the European starling, under naturally changing day length. Although Dio2 expression varied seasonally, Dio3 did not. We found no correlation of Dio2 with photoperiod, seasonal regulation of GnRH, or testicular volume. The observed differences in data from starlings and quail could be a result of phylogeny, genetic drift from founder populations, or differences in reproductive seasonality in addition to or instead of arising from domestication or use of artificially changing photoperiods. Overall, the data indicate that in a wild species exposed to natural changes in day length, the current proposed mechanism for photoperiodic timing is less straightforward than is generally accepted and might not be as universally applicable as previously thought.

Body condition influences sexual signal expression independent of circulating androgens in male red-backed fairy-wrens

Androgens play a major role in the regulation of sexual signal expression of male vertebrates. In this study we assessed the prevalent, yet largely untested, assumption that signal honesty is maintained through condition-dependent androgen regulation by experimentally manipulating body condition of male red-backed fairy-wrens (Malurus melanocephalus) through trimming several flight feathers before the prenuptial molt. In their first reproductive season males of this species exhibit androgen-regulated plasticity in plumage coloration, ranging from red/black (high androgens) to brown (low androgens). Red/black plumage is preferred by females and might be constrained by a negative relationship between body condition and androgen levels. We also evaluated whether corticosterone changes to altered conditional state mediate the relationship between condition and androgens. While we predicted that males with trimmed feathers would expend greater energy and thus be in poorer condition at the time of molt, they were counter-intuitively in better condition compared to control birds, likely as a consequence of subtle behavioral changes. These birds in better condition molted a greater proportion of red/black plumage, as predicted, and also molted more heavily. However, experimental and control birds did not differ in their androgen or corticosterone concentrations. Furthermore, analysis of long-term data from the same population revealed no correlation between condition and androgen levels. Collectively, these results challenge the notion that condition-dependent androgen regulation alone is responsible for maintaining the honesty of sexual signals and highlights the necessity of considering alternate explanations.

Species- and tissue-specific accumulation of Dechlorane Plus in three terrestrial passerine bird species from the Pearl River Delta, South China

Little data is available on the bioaccumulation of Dechlorane Plus (DP) in terrestrial organisms. Three terrestrial passerine bird species, light-vented bulbul, long-tailed shrike, and oriental magpie-robin, were collected from rural and urban sites in the Pearl River Delta to analyze for the presence of DP and its dechlorinated products in muscle and liver tissues. The relationships between trophic level and concentration and isomeric composition of DP in birds were also investigated based on stable nitrogen isotope analysis. DP levels had a wide range from 3.9 to 930 ng g(-1)lipid weight (lw) in muscle and from 7.0 to 1300 ng g(-1)lw in liver. Anti-Cl(11)-DP and syn-Cl(11)-DP, two dechlorinated products of DP, were also detected in bird samples with concentrations ranged between not detected (nd)-41 and nd-7.6 ng g(-1)lw, respectively. DP preferentially accumulated in liver rather than in muscle for all three bird species. Birds had significantly higher concentrations of DP in urban sites than in rural sites (mean, 300 vs 73 ng g(-1)lw). The fractions of anti-DP (f(anti)) were higher in birds collected in rural sites than in urban sites. Significant positive correlation between DP levels and δ(15)N values but significant negative correlation between f(anti) and δ(15)N values were found for birds in both urban and rural sites, indicating that trophic level of birds play an important role in determining DP level and isomeric profile.

Influence of landscape composition and diversity on contaminant flux in terrestrial food webs: a case study of trace metal transfer to European blackbirds Turdus merula

Although understanding the influence of the spatial arrangement of habitats and interacting communities on the processes of pollutant flux and impacts is critical for exposure and risk assessment, to date few studies have been devoted to this emergent topic. We tested the hypothesis that landscape composition and diversity affect the transfer of trace metals to vertebrates. Bioaccumulation of Cd and Pb in blood and feathers of European blackbirds Turdus merula (n=138) was studied over a smelter-impacted area (Northern France). Landscape composition (type and occurrence of the different habitats) and diversity (number of different habitat types and the proportional area distribution among habitat types) were computed around bird capture locations. Diet composition and contamination were assessed. No sex-related differences were detected, while age-related patterns were found: yearlings showed a sharper increase of tissue residues along the pollution gradient than older birds. Factors determining bird exposure acted at nested spatial scale. On a broad scale, environmental contamination mainly influenced metal levels in blackbirds, tissue residues increasing with soil contamination. At a finer grain, landscape composition and soil properties (pH, organic matter, clay) influenced metal transfer, while no influence of landscape diversity was detected. Landscape composition better explained metal transfer than soil properties did. Diet composition varied according to landscape composition, but diet diversity was not influenced by landscape diversity. Surprisingly, metal accumulation in some insect taxa was as high as in earthworms (known as hyper-accumulators). Results strongly suggested that variations in diet composition were the drivers through which landscape composition influenced metal transfer to blackbirds. This study shows that landscape features can affect pollutant transfer in food webs, partly through ecological processes related to spatial and foraging behavior of birds, and brings evidences underpinning the need to better consider landscape in environmental risk assessment and management of contaminated lands.

Experimental evidence for the interplay of exogenous and endogenous factors on the movement ecology of a migrating songbird

Movement patterns during songbird migration remain poorly understood despite their expected fitness consequences in terms of survival, energetic condition and timing of migration that will carry over to subsequent phases of the annual cycle. We took an experimental approach to test hypotheses regarding the influence of habitat, energetic condition, time of season and sex on the hour-by-hour, local movement decisions of a songbird during spring stopover. To simulate arrival of nocturnal migrants at unfamiliar stopover sites, we translocated and continuously tracked migratory red-eyed vireos (Vireo olivaceus) throughout spring stopover with and without energetic reserves that were released in two replicates of three forested habitat types. Migrants moved the most upon release, during which time they selected habitat characterized by greater food abundance and higher foraging attack rates. Presumably under pressure to replenish fuel stores necessary to continue migration in a timely fashion, migrants released in poorer energetic condition moved faster and further than migrants in better condition and the same pattern was true for migrants released late in spring relative to those released earlier. However, a migrant's energetic condition had less influence on their behavior when they were in poor quality habitat. Movement did not differ between sexes. Our study illustrates the importance of quickly finding suitable habitat at each stopover site, especially for energetically constrained migrants later in the season. If an initial period prior to foraging were necessary at each stop along a migrant's journey, non-foraging periods would cumulatively result in a significant energetic and time cost to migration. However, we suggest behavior during stopover is not solely a function of underlying resource distributions but is a complex response to a combination of endogenous and exogenous factors.

Anticipating spring: wild populations of great tits (Parus major) differ in expression of key genes for photoperiodic time measurement

Measuring day length is critical for timing annual changes in physiology and behavior in many species. Recently, rapid changes in several photoperiodically-controlled genes following exposure to a single long day have been described. Components of this 'first day release' model have so far only been tested in highly domesticated species: quail, sheep, goats and rodents. Because artificial selection accompanying domestication acts on genes related to photoperiodicity, we must also study this phenomenon in wild organisms for it to be accepted as universal. In a songbird, the great tit (Parus major), we tested whether a) these genes are involved in photoperiodic time measurement (PTM) in a wild species, and b) whether predictable species and population differences in expression patterns exist. Using quantitative RT-PCR, we compared gene expression after a single long day in male great tits from Sweden (57°42'N) with that from a German (47°43'N) population. Hypothalamic gene expression key for PTM changed only in the northern population, and occurred earlier after dawn during the single long day than demonstrated in quail; however, gonadotropins (secretion and synthesis) were stimulated in both populations, albeit with different timing. Our data are the first to show acute changes in gene expression in response to photostimulation in any wild species not selected for study of photoperiodism. The pronounced differences in gene expression in response to a single long day between two populations raise exciting new questions about potential environmental selection on photoperiodic cue sensitivity.

Understanding associations between nitrogen and carbon isotopes and mercury in three Ammodramus sparrows

We analyzed nitrogen and carbon stable isotope ratios and mercury (Hg) in breast feathers from three species of closely related sparrows, Saltmarsh, Seaside, and Nelson's Sparrows (Ammodramus caudacutus, A. maritimus, and A. nelsoni, respectively), to assess if trophic position and food web structure influence Hg exposure in these species. Sparrows were captured during the non-breeding season from 2006 to 2008 in North Carolina salt marshes near Wrightsville Beach, New Hanover County. Generalized linear models were used to test for the influence of species, δ(15)N, and δ(13)C on breast feather Hg. The most parsimonious model included species, δ(15)N, and their interaction term and explained 36% of the variation in breast feather Hg. Each species exhibited a different association between breast feather δ(15)N and Hg with Seaside Sparrows showing a positive correlation (r=0.27, P=0.03), Nelson's Sparrows a negative correlation (r=-0.28, P=0.01), and Saltmarsh Sparrows with no significant association. For Saltmarsh Sparrows, δ(15)N and Hg revealed decoupling between breast feather Hg and trophic position. Our results demonstrate that the influence of δ(15)N on breast feather Hg is likely indicative of geographic variation in δ(15)N baselines rather than trophic position.

Candidate genes for carotenoid coloration in vertebrates and their expression profiles in the carotenoid-containing plumage and bill of a wild bird

Carotenoid-based coloration has attracted much attention in evolutionary biology owing to its role in honest, condition-dependent signalling. Knowledge of the genetic pathways that regulate carotenoid coloration is crucial for an understanding of any trade-offs involved. We identified genes with potential roles in carotenoid coloration in vertebrates via (i) carotenoid uptake (SR-BI, CD36), (ii) binding and deposition (StAR1, MLN64, StAR4, StAR5, APOD, PLIN, GSTA2), and (iii) breakdown (BCO2, BCMO1). We examined the expression of these candidate loci in carotenoid-coloured tissues and several control tissues of the red-billed quelea (Quelea quelea), a species that exhibits a male breeding plumage colour polymorphism and sexually dimorphic variation in bill colour. All of the candidate genes except StAR1 were expressed in both the plumage and bill of queleas, indicating a potential role in carotenoid coloration in the quelea. However, no differences in the relative expression of any of the genes were found among the quelea carotenoid phenotypes, suggesting that other genes control the polymorphic and sexually dimorphic variation in carotenoid coloration observed in this species. Our identification of a number of potential carotenoid genes in different functional categories provides a critical starting point for future work on carotenoid colour regulation in vertebrate taxa.

Convergent differential regulation of parvalbumin in the brains of vocal learners

Spoken language and learned song are complex communication behaviors found in only a few species, including humans and three groups of distantly related birds – songbirds, parrots, and hummingbirds. Despite their large phylogenetic distances, these vocal learners show convergent behaviors and associated brain pathways for vocal communication. However, it is not clear whether this behavioral and anatomical convergence is associated with molecular convergence. Here we used oligo microarrays to screen for genes differentially regulated in brain nuclei necessary for producing learned vocalizations relative to adjacent brain areas that control other behaviors in avian vocal learners versus vocal non-learners. A top candidate gene in our screen was a calcium-binding protein, parvalbumin (PV). In situ hybridization verification revealed that PV was expressed significantly higher throughout the song motor pathway, including brainstem vocal motor neurons relative to the surrounding brain regions of all distantly related avian vocal learners. This differential expression was specific to PV and vocal learners, as it was not found in avian vocal non-learners nor for control genes in learners and non-learners. Similar to the vocal learning birds, higher PV up-regulation was found in the brainstem tongue motor neurons used for speech production in humans relative to a non-human primate, macaques. These results suggest repeated convergent evolution of differential PV up-regulation in the brains of vocal learners separated by more than 65–300 million years from a common ancestor and that the specialized behaviors of learned song and speech may require extra calcium buffering and signaling.

Assessing the cost of helping: the roles of body condition and oxidative balance in the Seychelles warbler (Acrocephalus sechellensis)

In cooperatively breeding species, helping close relatives may provide important fitness benefits. However, helping can be energetically expensive and may result in increased generation of reactive oxygen species. Consequently, an oxidant/antioxidant imbalance can lead to higher oxidative stress susceptibility. Given the potential costs of helping, it may be that only individuals with a sufficiently good body condition and/or stable oxidative balance can afford to help. Knowledge about relationships between social status and oxidative balance in cooperatively breeding systems is still limited. Studying these relationships is important for understanding the costs of helping and physiological pressures of reproduction. Here we evaluate the relationship between helping behaviour, body condition and oxidative balance in a wild population of the cooperatively breeding Seychelles warbler (Acrocephalus sechellensis). In this species, some subordinate individuals help dominant birds with the rearing of young, while others refrain from any assistance. We assessed body condition and oxidative parameters of birds of different social status caught during different breeding stages. We found that, prior to breeding, female subordinates that did not subsequently help (non-helpers) had significantly lower body condition and higher ROMs (reactive oxygen metabolites) than helpers and dominants. During the later stages of breeding, body condition was low in dominants and helpers, but high in non-helpers. Differences in oxidative balance between individuals of different social status were found only during nest care: Dominant males occupied with guarding behaviours tended to have relatively high oxidative stress susceptibility. Furthermore, dominant and helper females showed elevated antioxidant capacity (measured as OXY) in the weeks just prior to egg-laying, possibly representing a change in their reproductive physiology. The results imply that an individuals' oxidative balance may be influenced by factors related to reproduction, which can differ with sex and--within cooperative breeding systems--social status.

Aggressive interactions differentially modulate local and systemic levels of corticosterone and DHEA in a wild songbird

During the nonbreeding season, when gonadal androgen synthesis is basal, recent evidence suggests that neurosteroids regulate the aggression of male song sparrows. In particular, dehydroepiandrosterone (DHEA) is rapidly converted in the brain to androgens in response to aggressive interactions. In other species, aggressive encounters increase systemic glucocorticoid levels. However, the relationship between aggression and local steroid levels is not well understood. Here, during the breeding and nonbreeding seasons, we tested the effects of a simulated territorial intrusion (STI) on DHEA and corticosterone levels in the brachial and jugular plasma. Jugular plasma is enriched with neurosteroids and provides an indirect index of brain steroid levels. Further, during the nonbreeding season, we directly measured steroid levels in the brain and peripheral tissues. Both breeding and nonbreeding males displayed robust aggressive responses to STI. During the breeding season, STI increased brachial and jugular corticosterone levels and jugular DHEA levels. During the nonbreeding season, STI did not affect plasma corticosterone levels, but increased jugular DHEA levels. During the nonbreeding season, STI did not affect brain levels of corticosterone or DHEA. However, STI did increase corticosterone and DHEA concentrations in the liver and corticosterone concentrations in the pectoral muscle. These data suggest that 1) aggressive social interactions affect neurosteroid levels in both seasons and 2) local steroid synthesis in peripheral tissues may mobilize energy reserves to fuel aggression in the nonbreeding season. Local steroid synthesis in brain, liver or muscle may serve to avoid the costs of systemic increases in corticosterone and testosterone.

Seasonal and population variation in male testosterone levels in breeding orange-crowned warblers (Vermivora celata)

Comparative hormone studies can reveal how physiology underlies life history variation. Here, we examined seasonal variation in plasma testosterone concentration between populations of male orange-crowned warblers (Vermivora celata) breeding in Fairbanks, Alaska (V. c. celata) and on Santa Catalina Island, California (V. c. sordida). These populations face different ecological constraints and exhibit different life histories. Alaska birds have a short breeding season, low annual adult survival, and high reproductive rates. In contrast, Catalina Island birds exhibit high adult survival and low reproductive rates despite having a long breeding season. We examined seasonal variation in male testosterone concentrations as a potential mechanism underlying differences in male reproductive strategies between populations. From 2006 to 2008, we sampled males during the pre-incubation, incubation, and nestling stages. Alaska males exhibited a seasonal testosterone pattern typical of northern passerines: testosterone levels were high during pre-incubation and declined during incubation to low levels during nestling provisioning. Testosterone concentrations in Catalina Island males, however, did not vary consistently with breeding stage, remained elevated throughout the breeding season, and were higher than in Alaska males during the nestling stage. We hypothesize that in Alaska, where short seasons and high adult mortality limit breeding opportunities, the seasonal testosterone pattern facilitates high mating effort prior to incubation, but high parental investment during the nestling stage. On Catalina Island, elevated testosterone levels may reflect the extended mating opportunities and high population density facing males in this population. Our results suggest that population variation in seasonal testosterone patterns in orange-crowned warblers may be a function of differences in life history strategy and the social environment.

[Estimation of heritability and repeatability of resting metabolic rate in birds, with free-living pied flycatchers Ficedula hypoleuca (Aves: Passeriformes) as an example]

Estimates of a trait heritability and repeatability can get at an idea of its usefulness for being an individual characteristic and its ability to change under selection pressure. Heritability and repeatability of energetic parameters still poorly studied in birds. The most important physiological characteristic of homoiotherms is resting metabolic rate (RMR), which, in the absence of productive processes, does not exceed basal metabolic rate (BMR). We estimated BMR repeatability in free-living pied flycatchers in Moscow Region (55 degrees 44' N, 36 degrees 51' E; 1992-2008) and Tomsk (56 degrees 20' N, 84 degrees 56' E; 2008-2009) populations over intervals from 40 days to 3 years. In Moscow Region population, BMR repeatability amounted to tau = 0.34 +/- 0.10 (n=80) if measured over 1 year interval, tau = 0.60 +/- 0.15 (n=19) if measured over 2 years interval, and tau = 0.85 +/- 0.13 (n=6) if measured over 3 years interval providing that consecutive BMR measurements were done in the same period of reproductive season. In Tomsk population, BMR repeatability, measured over 1 year interval, amounted to tau = 0.49 +/- 0.11 (n=50). Repeatability is a measure of a trait constancy and sets the upper limit of its heritability. To estimate RMR heritability, cross-fostering experiments have been conducted in 2003-2005 with flycatchers of Moscow Region population. RMR of chicks positively correlated with BMR of their biological fathers, whereas such correlation in metabolic rates between chicks and their foster fathers was absent. The RMR heritability estimate turned out to be h2 = 0.43 +/- 0.17 (n=210). The obtained estimates of heritability and repeatability of fundamental energetic traits are rather high for physiological features. This suggests the existence of a potential for direct selection on BMR and evolutionary stable diversity of avian populations with regard to basal metabolic rate.