Calcium availability affects bone growth in nestlings of free-living great tits (Parus major), as detected by plasma alkaline phosphatase

Fecal calcium levels of bird nestlings as a potential indicator of species-specific metal sensitivity

Sensitivity of bird species to environmental metal pollution varies but there is currently no general framework to predict species-specific sensitivity. Such information would be valuable from a conservation point-of-view. Calcium (Ca) has antagonistic effects on metal toxicity and studies with some common model species show that low dietary and circulating calcium (Ca) levels indicate higher sensitivity to harmful effects of toxic metals. Here we measured fecal Ca and five other macroelement (potassium K, magnesium Mg, sodium Na, phosphorus P, sulphur S) concentrations as proxies for dietary levels in 66 bird species to better understand their interspecific variation and potential use as an indicator of metal sensitivity in a wider range of species (the main analyses include 39 species). We found marked interspecific differences in fecal Ca concentration, which correlated positively with Mg and negatively with Na, P and S levels. Lowest Ca concentrations were found in insectivorous species and especially aerial foragers, such as swifts (Apodidae) and swallows (Hirundinidae). Instead, ground foraging species like starlings (Sturnidae), sparrows (Passeridae), cranes (Gruidae) and larks (Alaudidae) showed relatively high fecal Ca levels. Independent of phylogeny, insectivorous diet and aerial foraging seem to indicate low Ca levels and potential sensitivity to toxic metals. Our results, together with information published on fecal Ca levels and toxic metal impacts, suggest that fecal Ca levels are a promising new tool to evaluate potential metal-sensitivity of birds, and we encourage gathering such information in other bird species. Information on the effects of metals on breeding parameters in a wider range of bird species would also help in ranking species by their sensitivity to metal pollution.

Vitamin profiles in two free-living passerine birds under a metal pollution gradient - A calcium supplementation experiment

Vitamin and carotenoid deficiency may impair development in free-living vertebrates, because of the importance of these micronutrients to growth, antioxidant defense and calcium regulation. Micronutrient and calcium insufficiency can be intensified by metal pollution which can interfere with nutrient homeostasis or indirectly reduce food availability. Furthermore, absorption of dietary heavy metals is dependent on food calcium and vitamin levels. We investigated the effect of calcium on plasma vitamin and carotenoid profiles and how these affected growth and survival in two passerine birds with different calcium turnover living along a metal pollution gradient. Vitamins (A, D₃ and E) and carotenoids were quantified from blood plasma of great tit (Parus major) and pied flycatcher (Ficedula hypoleuca) nestlings. Metal concentrations in soil and in feces from the same nestlings were used to assess the exposure to air pollution. Additionally, we examined the vitamin level variation between developmental stages (eggs and nestlings within the same brood). Our results showed that generally higher concentrations of vitamins and carotenoids circulate in blood of great tits than in pied flycatchers. In general, birds inhabiting the polluted zone presented lower concentrations of the studied micronutrients. Calcium supplementation and metal pollution decreased vitamin A concentration in pied flycatcher, but not in great tit, while vitamin A affected growth and survival in great tit and pied flycatcher respectively. Our results suggest that populations under exposure to metal pollution may experience increased vitamin A deficiency, and that the two passerine species, while obtaining similar micronutrients in food, respond differently to environmental disturbance of nutrients.

Sex roles, parental care and offspring growth in two contrasting coucal species

The decision to provide parental care is often associated with trade-offs, because resources allocated to parental care typically cannot be invested in self-maintenance or mating. In most animals, females provide more parental care than males, but the reason for this pattern is still debated in evolutionary ecology. To better understand sex differences in parental care and its consequences, we need to study closely related species where the sexes differ in offspring care. We investigated parental care in relation to offspring growth in two closely related coucal species that fundamentally differ in sex roles and parental care, but live in the same food-rich habitat with a benign climate and have a similar breeding phenology. Incubation patterns differed and uniparental male black coucals fed their offspring two times more often than female and male white-browed coucals combined. Also, white-browed coucals had more 'off-times' than male black coucals, during which they perched and preened. However, these differences in parental care were not reflected in offspring growth, probably because white-browed coucals fed their nestlings a larger proportion of frogs than insects. A food-rich habitat with a benign climate may be a necessary, but-perhaps unsurprisingly-is not a sufficient factor for the evolution of uniparental care. In combination with previous results (Goymann et al. 2015 J. Evol. Biol. 28, 1335-1353 (doi:10.1111/jeb.12657)), these data suggest that white-browed coucals may cooperate in parental care, because they lack opportunities to become polygamous rather than because both parents were needed to successfully raise all offspring. Our case study supports recent theory suggesting that permissive environmental conditions in combination with a particular life history may induce sexual selection in females. A positive feedback loop among sexual selection, body size and adult sex-ratio may then stabilize reversed sex roles in competition and parental care.

Skeletal Pathology in White Storks (Ciconia ciconia) Associated With Heavy Metal Contamination in Southwestern Spain

In 1998, a mine tailings dyke in southwestern Spain broke, flooding the Agrio-Guadiamar river system with acid tailings up to the borders of one of the largest breeding colony of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects, prompting this study. Ten fledglings with leg deformities from the spill area were compared with 11 normal storks of the same year class from another region far from the spill. However, metals were analyzed as a continuum rather than by site, as reference birds also contained high levels of metals. Gross pathology of the legs was supported by histopathology, which showed that bone remodeling activity was greater in the deformed storks, which also had more irregular subperiosteal bone, and tended to have higher residual islets of cartilage in their metaphyses, which, in turn were related to metal contaminant residues. Both Ca and P in bone were affected independently by metals. Deformed birds had lower serum bone alkaline phosphatase. Bone malformations, measured by leg asymmetry, was only partially explained by bone metals, indicating that a combination of factors was involved with the abnormal development in these young storks.

Effects of calcium supplementation on growth and biochemistry in two passerine species breeding in a Ca-poor and metal-polluted area

Several studies provide evidence of calcium (Ca)-limited reproduction in birds. A Ca-supplementation experiment was carried out in 2014 in a Ca-poor area associated with metal pollution in SW Finland. We aimed to evaluate the relationship between Ca availability and heavy metal exposure in free-living passerines, and to compare Ca levels in plasma and feces and the effects of Ca supplementation and metals on breeding, nestling growth, and plasma biochemistry in great tits and pied flycatchers. Although the Ca supplement was used by parents, in general the treatment had limited effects on growth and biochemistry, suggesting that parents are capable of finding sufficient Ca-rich foods to allow nestlings to grow properly. Snail shells were an abundant Ca source in the moderately polluted zone for pied flycatcher, and great tits likely combines the intake of snail shells and other anthropogenic Ca-rich items. Great tits had higher Ca concentrations in feces and plasma than pied flycatcher nestlings, suggesting that they need and sustain higher Ca levels and seem to be more opportunistic in search for Ca than pied flycatcher, since they consumed more of the supplemented Ca. Negative effects of pollution in nestling size and fledgling number were found in great tit. This species may suffer especially from the lower food quality and quantity in the polluted area. The pied flycatcher seems to be adapted to low Ca availability and they can successfully breed when metal concentrations are not too high. Our results show that great tits and pied flycatchers may employ different strategies in response to low Ca availability.

Experimental manipulation of dietary lead levels in great tit nestlings: limited effects on growth, physiology and survival

We manipulated dietary lead (Pb) levels of nestlings in wild populations of the great tit (Parus major L) to find out if environmentally relevant Pb levels would affect some physiological biomarkers (haematocrit [HT], fecal corticosterone metabolites [CORT], heat shock proteins [HSPs], erythrocyte delta-aminolevulinic acid dehydratase activity [ALAd]), growth (body mass, wing length), phenotype (plumage coloration) or survival of nestlings. The responses to three experimental manipulation (control, low and high: 0, 1 and 4 μg/g body mass/day) are compared with those in a P. major population breeding in the vicinity of a heavy metal source, a copper smelter. Our Pb supplementation was successful in raising the fecal concentrations to the levels found in polluted environments (high: 8.0 μg/g d.w.). Despite relatively high range of exposure levels we found only few effects on growth rates or physiology. The lack of blood ALAd inhibition suggests that the circulating Pb levels were generally below the toxic level despite that marked accumulation of Pb in femur (high: 27.8 μg/g d.w.) was observed. Instead, birds in the metal polluted environment around the smelter showed decreased growth rates, lower HT, higher CORT, less colorful plumage and lower survival probabilities than any of the Pb treated groups. These effects are likely related to decreased food quality/quantity for these insectivorous birds at the smelter site. In general, the responses of nestlings to metal exposure and/or associated resource limitation were not gender specific. One of the stress proteins (HSP60), however, was more strongly induced in Pb exposed males and further studies are needed to explore if this was due to higher accumulation of Pb or higher sensitivity of males. In all, our results emphasize the importance of secondary pollution effects (e.g. via food chain disruption) on reproductive output of birds.

Can fruit pulp meet the calcium needs of tropical frugivorous passerines during reproduction?

Calcium is an important nutrient for birds, especially for eggshell production and the mineralization of the skeleton of developing young. In temperate regions insects and seeds that form the bulk of the diet of breeding passerines do not contain sufficient calcium to meet the needs of breeding females and young; these birds obtain their calcium by eating snails, woodlice and millipedes. Little is known about the way tropical frugivorous passerines meet their calcium needs. The calcium contents of fruits of 34 species eaten by birds during the breeding season in mature floodplain forest in south-eastern Peru were determined. The suitability of these fruits as calcium sources for hypothetical 10-g and 25-g birds and for 26 species of frugivore that breed at the study site was evaluated based on bird body weight and on the rictal width of the bill, which influences feeding. Fruits of five species in the study area appear to be suitable sources of calcium for birds ≤25 g, although those of Ficus killipii (Moraceae) are likely optimal. The latter contain a lot of calcium (2.48% dry weight of pulp or c. 4.15 mg per pulp per fruit) and are small enough (mean diam. = 9 mm) for most birds to swallow whole, and trees produce large crops. Snails, woodlice and millipedes are common in the area and also contain sufficient calcium to meet birds’ needs. In addition, birds could likely meet their calcium needs through geophagy at natural mineral licks.

Plasma alkaline phosphatase as a sensitive indicator of age and skeletal development in wild coscoroba swans

Context. Recent studies have suggested that plasma alkaline phosphatase (ALP) can be used to assess skeletal development as well as health status in wild animals. Aims. However, the information about age-related dynamics of ALP in birds, especially in precocial species, is very scarce. Therefore, before ALP measurements can be effectively interpreted, it is necessary to determine its normal variation for each species, age group and sex. Methods. Here, we report total-ALP levels of free-living coscoroba swans (Coscoroba coscoroba) from the most important breeding and moulting population in Brazil. Data were gathered during the moulting period and categorised according to sex and the following three different age classes: chick (n = 11), young (n = 14) and mature (n = 29). Key results. ALP levels were related to the longitudinal measure of the bones, gradually diminishing with age and showing significant differences among birds of different age classes. In all age groups, no effect of sex on T-ALP concentration was detected. Conclusions. We conclude that measuring ALP facilitates the discrimination among different-aged individuals with similar plumage characteristics and body size.

Calcium effects on life-history traits in a wild population of the great tit (Parus major): analysis of long-term data at several spatial scales

Calcium is an essential micronutrient for birds during egg formation and for skeletal development in nestlings. Habitat level studies suggest that birds breeding in low-calcium areas may be limited in the size or number of eggs they lay and in the quality of their nestlings. However, as birds forage non-randomly and may travel considerable distances to acquire calcium, describing different breeding environments in terms of their calcium availability is problematic. Here we explore the spatial relationships between 300-fold variation in soil calcium and the life-history traits of ca. 6,000 pairs of great tits breeding in a single continuous woodland over 41 years. Controlling for other habitat differences, we found strong positive associations between soil calcium, clutch size and recruitment at spatial scales of over 300 m from each nestbox, suggesting that females may have been travelling inter-territorially to acquire calcium during egg formation. Soil calcium near each nestbox (mean distance = 58 m) was a strong positive predictor of mean fledgling mass, suggesting that local calcium was more important during nestling stages. We found no effect of soil calcium on lay-date or egg mass. This study is the first to provide evidence that small woodland passerines are limited by calcium availability at several different spatial scales. However, experimental work is necessary to test the causality of these spatial patterns.

Is there life in the horny layer? Dihydropyridine and ryanodine receptors in the skin of female and male chickens (Gallus domesticus)

Previous findings in pigeons and chickens show that Ca(2+) may be accumulated inside the cornified skin cells and that Ca(2+) microenvironments with a lower- or higher-than-blood concentration may exist in the skin. It has been suggested that the skin may function as a secretory pathway or a reservoir for Ca(2+) recycling. To test this hypothesis, we studied the dermis and epidermis of female and male chickens in vivo to find out whether cellular mechanisms exist for the accumulation, recycling or secretion of Ca(2+). For calcium influx and intracellular Ca(2+) release, respectively, the density of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs) was examined, using high-affinity (-)-enantiomers of dihydropyridine and ryanodine labelled with fluorophores. To investigate Ca(2+) utilization in the skin, the systemic and local activity of the enzyme alkaline phosphatase (ALP) and the concentration of ionic Ca(2+) were measured in plasma and in cutaneous extracellular fluid, collected by suction blister technique. We found that both DHPRs and RyRs were present in all skin layers from dermis to horny layer. However, receptor densities were highest in the surface layers. With a basic calcium-rich diet, receptor densities were higher in males, particularly in the dermis and mid-epidermis. After a reduction in the nutritional Ca(2+) input, receptor densities in males decreased to the same level as in females, in which the receptor densities were not affected by the amount of Ca(2+) in the diet or that resulting from coming out of lay. The extracellular concentration of ionic Ca(2+) per se was not found to affect the density of DHPRs and RyRs in the skin. Spatially, RyRs seem to be located in the periphery of the sebokeratinocyte. ALP activity was shown to be lower in the extracellular fluid than in the plasma in both sexes. However, activity in both extracellular domains increased significantly in females that had come out of lay. This was probably connected with the increased osteoblast activity related to the reformation of structural bone. In conclusion, voltage-sensitive L-type Ca(2+) channels for ion influx and RyRs for Ca(2+) release are present in the cells of the skin of female and male chickens. Higher densities in the males receiving excessive Ca(2+) imply an increased capacity for Ca(2+) influx and intracellular processing. Even though the functional interactions between DHPRs and RyRs in the sebokeratinocytes could not be demonstrated, peripheral colocation and high receptor densities at the level of exocytosis of the lamellar bodies point to their role as part of a signalling pathway for secretion. The finding that DHPRs and RyRs are present in the horny layer implies that the function of the outermost skin might be more active than had been previously thought and that this function might be both secretory and sensory.

The rate of bone mineralization in birds is directly related to alkaline phosphatase activity

Recent studies have suggested that a biochemical marker, plasma alkaline phosphatase (ALP), can be used as a general indicator of skeletal development in vertebrate animals. In birds, age-related variation in ALP activity, presumably due to bone formation processes, has been demonstrated, but to date, a direct connection between bone mineralization and enzyme activity has been elusive. In this study, we show that the activity of a bone isoform of ALP (bone ALP) is closely related to the overall rate of skeletal mineralization in nestlings of a small passerine bird, the great tit (Parus major L). Moreover, bone ALP activity predicted the rate of mineralization of leg and wing bones but not that of the skull. Liver isoform of ALP was only marginally related to the overall rate of skeletal mineralization, while no association with the mineralization of long bones was found. We conclude that bone ALP activity in the blood plasma is a reliable biomarker for skeletal mineralization in birds. This marker enables detection of subtle developmental differences between chicks of similar structural size, potentially facilitating the prediction of offspring mid- and long-term survival.

Disrupted bone metabolism in contaminant-exposed white storks (Ciconia ciconia) in southwestern Spain

In 1998, the Aznalcóllar mine tailings dyke in southwestern Spain broke, flooding the Agrio-Guadiamar river system with acid tailings up to the borders of one of the largest breeding colonies of white storks in the western Palearctic, Dehesa de Abajo. Over the following years, a high proportion of nestlings developed leg defects not seen before the spill, prompting this study. Nestlings with deformed legs had significantly lower plasma phosphorous (P) and higher Ca:P ratios than non-deformed cohorts in the first two years, but in the third year, when more, younger birds were studied, plasma P ranged from much higher to much lower in the affected colony compared with reference birds. Coefficients of variation for phosphorous were 19% and 60%, in reference and contaminated colonies, respectively. Storks from the contaminated colony were unable to control P levels and Ca:P ratios within the narrow limits necessary for normal bone development.

Environmental stress increases skeletal fluctuating asymmetry in the moor frog Rana arvalis

Whether fluctuating asymmetry (FA) provides a useful metric indicator of the degree of environmental stress experienced by populations is still a contentious issue. We investigated whether the degree of FA in skeletal elements is useful in elucidating the degree of environmental stress experienced by frog populations, and further, tested the proposition that a trait's sensitivity to stress--as reflected in the degree of FA--is related to the degree of directional selection experienced by the given trait. We compared the degree of FA in four bilateral skeletal elements of male and female moor frogs (Rana arvalis) originating from low (acidified) and neutral pH populations. While the degree of uncorrected FA was unrelated to the degree of acidity, the growth rate and age of the individuals, the size-corrected FA was significantly higher in low than in neutral pH populations and decreased with individual ages and growth rates. In addition, both measures of FA were significantly higher in males and in particular in traits presumably under high sexual selection as indicated by the degree of sexual size dimorphism. All in all, the results indicate that individuals from acidified localities are smaller, younger and exhibit a significantly higher degree of FA than individuals from neutral pH populations. These results constitute the first assessment of FA in amphibians and suggest that the degree of FA in skeletal traits can be a useful indicator of the degree of environmental stress experienced by amphibian populations.

Chick Development in Free‐Living Great Tits Parus major in Relation to Calcium Availability and Egg Composition

Evidence from a number of avian studies suggests that limitation of exogenous calcium (Ca) may reduce egg quality and retard nestling growth. However, it is poorly understood whether reduction in chick growth in Ca-poor areas is due to insufficient intake of dietary Ca or caused by maternal Ca limitation mediated through subtle changes in composition of eggs. In this study, we provide new evidence that Ca availability during egg formation may indeed affect egg composition and influence chick development of the great tit Parus major at early developmental stages. Ca-supplemented birds breeding in base-poor pine forests produced eggs with elevated yolk Ca concentration compared with controls, while no such effect of supplementation was detected in case of eggshell thickness. Nestling tarsus length in the first half of the nestling period was positively influenced by both yolk dry mass and yolk Ca concentration. The effect of supplementary Ca did not persist throughout the nestling period; initial effects of egg components disappeared as nestlings aged. We conclude that apparently normal eggs may harbor poor nutrient and mineral conditions for chick growth. Such subtle changes in composition of eggs can depress chick growth, especially in harsh years.