Chiara Morosinotto

Geographical variation in egg mass and egg content in a passerine bird.

Reproductive, phenotypic and life-history traits in many animal and plant taxa show geographic variation, indicating spatial variation in selection regimes. Maternal deposition to avian eggs, such as hormones, antibodies and antioxidants, critically affect development of the offspring, with long-lasting effects on the phenotype and fitness. Little is however known about large-scale geographical patterns of variation in maternal deposition to eggs. We studied geographical variation in egg components of a passerine bird, the pied flycatcher (Ficedula hypoleuca), by collecting samples from 16 populations and measuring egg and yolk mass, albumen lysozyme activity, yolk immunoglobulins, yolk androgens and yolk total carotenoids. We found significant variation among populations in most egg components, but ca. 90% of the variation was among individuals within populations. Population however explained 40% of the variation in carotenoid levels. In contrast to our hypothesis, we found geographical trends only in carotenoids, but not in any of the other egg components. Our results thus suggest high within-population variation and leave little scope for local adaptation and genetic differentiation in deposition of different egg components. The role of these maternally-derived resources in evolutionary change should be further investigated.

Geographical trends in the yolk carotenoid composition of the pied flycatcher (Ficedula hypoleuca)

Carotenoids in the egg yolks of birds are considered to be important antioxidants and immune stimulants during the rapid growth of embryos. Yolk carotenoid composition is strongly affected by the carotenoid composition of the female’s diet at the time of egg formation. Spatial and temporal differences in carotenoid availability may thus be reflected in yolk concentrations. To assess whether yolk carotenoid concentrations or carotenoid profiles show any large-scale geographical trends or differences among habitats, we collected yolk samples from 16 European populations of the pied flycatcher, Ficedula hypoleuca. We found that the concentrations and proportions of lutein and some other xanthophylls in the egg yolks decreased from Central Europe northwards. The most southern population (which is also the one found at the highest altitude) also showed relatively low carotenoid levels. Concentrations of β-carotene and zeaxanthin did not show any obvious geographical gradients. Egg yolks also contained proportionally more lutein and other xanthophylls in deciduous than in mixed or coniferous habitats. We suggest that latitudinal gradients in lutein and xanthophylls reflect the lower availability of lutein-rich food items in the northern F. hypoleuca populations and in montane southern populations, which start egg-laying earlier relative to tree phenology than the Central European populations. Similarly, among-habitat variation is likely to reflect the better availability of lutein-rich food in deciduous forests. Our study is the first to indicate that the concentration and profile of yolk carotenoids may show large-scale spatial variation among populations in different parts of the species’ geographical range. Further studies are needed to test the fitness effects of this geographical variation.

Plasticity in incubation behaviour under experimentally prolonged vulnerability to nest predation

Nest predation is the main cause of nest failures in many bird species. To counter this, birds have evolved different behavioural strategies to decrease the visibility of their nests, thus reducing the probability of nest detection. We manipulated the long-term perception of nest predation risk in pied flycatchers (Ficedula hypoleuca) by experimentally increasing the nest vulnerability to predators. We placed treatment and control nest-boxes for breeding pied flycatchers that appeared identical during the initial phase of breeding. But after the removal of a front panel, treatment boxes had an enlarged entrance hole, almost twice the initial diameter. This treatment increases actual predation risk and presumably parental perception of risk. Control boxes presented instead an entrance hole of the same size both before and after the manipulation. When breeding in enlarged entrance holes, females doubled the vigilance at the nest while males reduced the time spent at the nest, compared to pied flycatchers breeding in control boxes. Increased vulnerability of the nest site to predation risk, thus, induced pied flycatcher parents to increase nest vigilance while reducing their activity at the nest. These results highlight the existence of plasticity in incubation behaviours under long-term experimentally increased nest predation risk.

Species and abundance of ectoparasitic flies (Diptera) in pied flycatcher nests in Fennoscandia

BackgroundBirds host several ectoparasitic fly species with negative effects on nestling health and reproductive output, and with the capability of transmitting avian blood parasites. Information on the abundance and distribution of the ectoparasitic fly genera Ornithomya (Hippoboscidae) and Protocalliphora (Calliphoridae) in northern Europe is still generally poor, and we thus explored their geographic range and occurrence of these flies in the nests of a common avian model species, the pied flycatcher Ficedula hypoleuca.MethodsNests of F. hypoleuca were collected from 21 locations across Fennoscandia in summer 2013, across a latitudinal gradient (between 56 °N – 70 °N) and examined for the presence of fly puparia. Adult specimens of Ornithomya spp. were also collected for species identification. Fly species were identified morphologically and identifications confirmed with DNA barcoding.ResultsWe found three species: two louse-flies − Ornithomya chloropus and O. avicularia − and one blow-fly, Protocalliphora azurea. The prevalence of O. avicularia was higher in southern latitudes and this species was not encountered beyond 62 °N whereas O. chloropus and P. azurea occurred across the whole range of latitudes. The prevalence of O. chloropus further increased with increasing distance from the coast – a pattern not documented before. The three fly species showed no interspecific associations in their prevalence.ConclusionsOur study revealed relatively high prevalence for all the species (O. chloropus 59 %, O. avicularia 20 %, P. azurea 32 %), and an interesting spatial pattern in the prevalence of the two louse fly species. Our sample did not indicate any major range shifts towards the north for the southern species as compared to the information from the past. Morphological identification of O. chloropus did not match with the corresponding sequences published in the GenBank and taxonomy of this group calls for further studies.

Antioxidant Enzyme Activities Vary with Predation Risk and Environmental Conditions in Free-Living Passerine Birds

Prolonged physiological stress response may lead to an excessive production of reactive oxygen species (ROS) and ultimately to oxidative stress and severe fitness costs. We investigated whether natural variation in predation risk, induced by pygmy owls (Glaucidium passerinum), modifies the oxidative status of two free-living food-supplemented passerine bird species—the great tit (Parus major) and the willow tit (Poecile montanus)—in March 2012 and 2013. Predation risk significantly affected antioxidant enzyme activities of willow tits. Antioxidant enzyme activities (principal component factor 2 [PC2] representing glutathione-S-transferase and superoxide dismutase activities) were higher in high predation risk areas in 2013 than in low predation risk areas in the same year. Higher enzyme activities may suggest higher ROS production in birds living under high predation risk. In addition, antioxidant enzyme activities (PC2) were also higher in high predation risk areas in 2013 than in high predation risk areas in the previous year, 2012. This may represent variation in the risk represented by pygmy owls, which is probably inversely related to the natural fluctuations in the densities of their main prey, voles. In willow tits, PC1 (representing catalase, total glutathione, the ratio of reduced to oxidized glutathione, and protein carbonylation) was not affected by perceived predation risk, nor were antioxidant levels or enzyme activities in great tits. Higher enzyme activities observed in willow tits suggest that predator presence can modify the antioxidant status of avian prey, but the response also seem to be influenced by other environmental characteristics, like harsh winter conditions.

Food supplementation, but not predation risk, alters female antioxidant status during breeding

Predator presence and shortage of food resources can alter behavior and cause chronic physiological stress, with long-term detrimental effects on the prey. Recently, it has been hypothesized that cellular damage via oxidative stress could be associated with such effects. Variation in food availability and predation risk could modify the oxidative/antioxidant status of prey. However, data from wild populations is scarce and, importantly, the interactive effects of these major ecological factors on oxidative/antioxidant status are poorly understood. We present the first study in a wild vertebrate, addressing the combined effects of experimental food supplementation and increased predation risk (cues of Mustela erminea) on antioxidant status of female pied flycatchers (Ficedula hypoleuca). We tested the effects during breeding, assuming that such variation could modify the antioxidant cost of reproduction. Supplementary food increased female body mass, independently of predator treatment. However, timing of breeding and reproductive investment remained unaffected by the treatments. Principal component 1 (PC 1) of antioxidant levels [reflecting superoxidase dismutase (SOD), glutathione peroxidase (GPx), and glutathione (tGSH)] showed lower values in the food-supplemented than non-food-supplemented group. Neither PC 2 [reflecting catalase (CAT) and GSH/GSSG ratio] nor PC 1 was affected by predation risk, and further, predation risk did not alter the effect of supplementary food on either PC. These results suggest that food resources may have a stronger impact than predation risk on female antioxidant status during breeding. This is the first fully experimental study focusing on the interactive effects of key environmental variables on antioxidant status in wild vertebrates; more studies are however needed to understand the role of these factors in shaping the cost of reproduction.Significance statementPredator presence and shortage of food resources may modify animal behavior and cause chronic physiological stress response with long-term detrimental effects on the prey. Recently, it has been hypothesized that cellular damage via oxidative stress (i.e., imbalance between pro-oxidants and antioxidant defenses) could be associated with such effects, but evidence from wild populations is scarce. Importantly, the interactive effects of food and predation are not well understood. For the first time in a vertebrate, we experimentally studied the combined effects of food availability and (simulated) predation risk on antioxidant status, using wild breeding passerines. Higher food availability, but not increased perceived predation risk, lowered the antioxidant defenses. Predation risk did not alter the effect of supplementary food. The role of such interactions in shaping the cost of reproduction (via antioxidant/oxidative status) should be further studied.