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Some theoretical models predict that nestling begging must be a costly activity to transmit reliable information to parents about offspring hunger. One candidate cost is oxidative stress, which could impair growth or immune function. This hypothesis predicts that nestlings in a poor oxidative status should pay higher costs for a given amount of begging, hence beg at lower rates for a similar degree of hunger. To test this prediction, we experimentally induced a transient alteration of the oxidative status of Barn Swallow (Hirundo rustica) nestlings by administering them either a single dose of a pro-oxidant substance (BSO) or an antioxidant (vitamin E), and recorded their begging behaviour. Chicks treated with vitamin E increased their begging rates in the hours following treatment. However, and contrary to prediction, BSO nestlings did not decrease begging compared to controls. These inconsistent results are difficult to explain by the hypothesis that begging performance is mediated by the oxidative status of nestlings because chicks with an impaired oxidative status (the BSO group) begged the same as controls. Alternatively, vitamin E may alleviate the inhibitory effects on begging of stress responses mediated by glucocorticoids. This study suggests that oxidative costs of begging are minor or absent in this species. Future studies should consider alternative explanations for an association between oxidative status, antioxidant supplementation and begging behaviour, particularly those involving glucocorticoids.

Theoretical models indicate that the evolution of biparental care depends on how parents behaviorally negotiate their level of care in response to those of their partner and whether sexes and individuals consistently vary in their response (compensatory response). While compensatory response has been widely investigated empirically, its repeatability has rarely been assessed. In this study, we used a reaction norm approach to investigate the repeatability of the compensatory offspring provisioning of a parent after temporary removal of its partner in the pied flycatcher (Ficedula hypoleuca) across different breeding seasons and partners. We found that only females partially compensated for the short-term removal of the partner and their response was significantly repeatable across years while breeding with different partners. This study highlights the importance of considering among individual differences in negotiation rules to better understand the role of negotiation mechanisms in the evolution of parental care strategies.

Theoretical models indicate that the evolution of biparental care depends on how parents behaviourally negotiate their level of care in response to those of their partner and whether sexes and individuals consistently vary in their response (compensatory response). While the compensatory response has been widely investigated empirically, its repeatability has rarely been assessed. In this study, we used a reaction norm approach to investigate the repeatability of the compensatory offspring provisioning of a parent after temporary removal of its partner in the pied flycatcher (Ficedula hypoleuca) across different breeding seasons and partners. We found that only females partially compensated for the short-term removal of the partner and their response was significantly repeatable across years while breeding with different partners. This study highlights the importance of considering among individual differences in negotiation rules to better understand the role of negotiation mechanisms in the evolution of parental care strategies.

Host selection by insect vectors plays an important role in the transmission of vector-borne infectious diseases. Sex-biased infections are frequently reported in vertebrates and may be due to sex differences in susceptibility caused by, among others, the effect of sex hormones on immunity or by differential exposure to parasites. We captured biting midges and blackflies with recent blood meals in 51 blue tit nests during 2019 and 2021 and analyzed the meals to determine molecularly the sex of the bird that insect vectors fed on. By comparing the sex ratio in those samples to the sex-ratio of the nestlings in each nest we know whether vectors fed on their hosts randomly or showed a preference for a particular sex. Although the relationship between both sex-ratios was not significant, males were bitten more frequently than females in the second year. In addition, we used samples collected during 2022 to test for the possible effect of nestlings exposure to insect bites. To do this, we analyzed videos of the nestling activity inside nest-boxes recorded during the period of maximum activity of vectors, and explore the exposure of each nestling to insect bites based on their position within the nest (time spent above or below other nestlings). Finally, we test whether exposure was related to the risk to be bitten by identifying nestlings molecularly from each blood meal recovered from vectors. These results will help to understand the mechanisms of host preference for flying insect vectors and the transmission of wildlife pathogens.

Theoretical models indicate that the evolution of biparental care depends onhow parents behaviourally negotiate their level of care in response to thoseof their partner and whether sexes and individuals consistently vary in theirresponse (compensatory response). While the compensatory response hasbeen widely investigated empirically, its repeatability has rarely beenassessed. In this study, we used a reaction norm approach to investigatethe repeatability of the compensatory offspring provisioning of a parentafter temporary removal of its partner in the pied flycatcher (Ficedula hypo-leuca) across different breeding seasons and partners. We found that onlyfemales partially compensated for the short-term removal of the partnerand their response was significantly repeatable across years while breedingwith different partners. This study highlights the importance of consideringamong individual differences in negotiation rules to better understand therole of negotiation mechanisms in the evolution of parental care strategies.

Presentamos los resultados de un estudio sobre la diversidad de derméstidos que habitan los nidos de una especie de ave troglodita, el herrerillo común (Cyanistes caeruleus), así como el efecto sobre estos Coleópteros de diversos factores, entre ellos la temperatura y la humedad relativa en el interior del nido. Se identificaron diez taxones, seis como especies reconocidas y cuatro como taxones larvarios identificados a nivel de género. La mayoría de los derméstidos encontrados, en estado larvario, eran derméstidos nidícolas del género Anthrenus. Los ejemplares de derméstidos necrobiontes (aquellos que se alimentan de cadáveres tanto en fase larvaria como adulta) se encontraron en menor proporción, y casi siempre en estado adulto. En los nidos de herrerillo donde se aumentó experimentalmente la temperatura se encontraron más larvas de derméstidos que en los nidos control, y en aquellos nidos donde se registraron valores más altos de temperatura se encontraron más derméstidos adultos necrobiontes del género Dermestes.

Extra-pair paternity (EPP) is the consequence of the interactions between a social pair and extra-pair males during the female's fertile phase in a specific social context and ecological environment. Although EPP occurs in many avian species, there is a lack of understanding of how environmental factors may impact its frequency. Accordingly, the relative importance of individual characteristics on the one hand, and of their immediate social environment on the other, may affect EPP repeatability and thereby the capacity of this trait to respond to selection. If EPP is an individual genetically based trait that may respond to selection, we expect it to be repeatable across breeding seasons. To check this possibility, we analysed the within-individual repeatability in EPP of breeding males and females in two natural populations of Pied Flycatchers Ficedula hypoleuca in central Spain during three field seasons. We then studied the relationship between EPP and individual male and female traits (only some of which were themselves repeatable), as well as key context variables such as breeding synchrony and population density. Our results showed no repeatability for EPP in either sex. We found a positive association with laying date and stronger associations of EPP with male plumage and morphological traits than with female characteristics. We suggest that the variable social environment is an important modulator of EPP patterns, and that differences between field EPP studies in this respect may explain contradictory results in the same species, even in the same populations in different years.

Extra-pair paternity (EPP) is the consequence of the interactions between a social pair and extra-pair males during the female’s fertile phase in a specific social context and ecological environment. Although EPP occurs in many avian species, there is a lack of understanding of how environmental factors may impact its frequency. Accordingly, the relative importance of individual characteristics on the one hand, and of their immediate social environment on the other, may affect EPP repeatability and thereby the capacity of this trait to respond to selection. If EPP is an individual genetically based trait that may respond to selection, we expect it to be repeatable across breeding seasons. To check this possibility, we analysed the within-individual repeatability in EPP of breeding males and females in two natural populations of Pied Flycatchers Ficedula hypoleuca in central Spain during three field seasons. We then studied the relationship between EPP and individual male and female traits (only some of which were themselves repeatable), as well as key context variables such as breeding synchrony and population density. Our results showed no repeatability for EPP in either sex. We found a positive association with laying date and stronger associations of EPP with male plumage and morphological traits than with female characteristics. We suggest that the variable social environment is an important modulator of EPP patterns, and that differences between field EPP studies in this respect may explain contradictory results in the same species, even in the same populations in different years.

Dataset of the scientific article "Heterozygosity, genetic similarity and extra-pair paternity variation in two populations of Rock Sparrow Petronia petronia: a within- and between- populations comparison".

Oscine birds preferentially respond to certain sounds over others from an early age, which focuses subse-quent learning onto sexually relevant songs.1-3 Songs vary both across species and, due to cultural evolution, among populations of the same species. As a result, early song responses are expected to be shaped by se-lection both to avoid the fitness costs of cross-species learning4 and to promote learning of population -typical songs.5 These sources of selection are not mutually exclusive but can result in distinct geographic patterns of song responses in juvenile birds: if the risks of interspecific mating are the main driver of early song discrimination, then discrimination should be strongest where closely related species co-occur.4 In contrast, if early discrimination primarily facilitates learning local songs, then it should be tuned to songs typical of the local dialect.5-7 Here, we experimentally assess the drivers of song discrimination in nestling pied flycatchers (Ficedula hypoleuca). We first demonstrate that early discrimination against the songs of the closely related collared flycatcher (F. albicollis) is not strongly affected by co-occurrence. Second, across six European populations, we show that nestlings' early song responses are tuned to their local song dialect and that responses to the songs of collared flycatchers are similarly weak as to those of other conspecific dialects. Taken together, these findings provide clear experimental support for the hypothesis that cultural evolution, in conjunction with associated learning predispositions, drives the emergence of pre-mating reproductive barriers.

Oscine birds preferentially respond to certain sounds over others from an early age, which focuses subsequent learning onto sexually relevant songs.1,2,3 Songs vary both across species and, due to cultural evolution, among populations of the same species. As a result, early song responses are expected to be shaped by selection both to avoid the fitness costs of cross-species learning4 and to promote learning of population-typical songs.5 These sources of selection are not mutually exclusive but can result in distinct geographic patterns of song responses in juvenile birds: if the risks of interspecific mating are the main driver of early song discrimination, then discrimination should be strongest where closely related species co-occur.4 In contrast, if early discrimination primarily facilitates learning local songs, then it should be tuned to songs typical of the local dialect.5,6,7 Here, we experimentally assess the drivers of song discrimination in nestling pied flycatchers (Ficedula hypoleuca). We first demonstrate that early discrimination against the songs of the closely related collared flycatcher (F. albicollis) is not strongly affected by co-occurrence. Second, across six European populations, we show that nestlings¿ early song responses are tuned to their local song dialect and that responses to the songs of collared flycatchers are similarly weak as to those of other conspecific dialects. Taken together, these findings provide clear experimental support for the hypothesis that cultural evolution, in conjunction with associated learning predispositions, drives the emergence of pre-mating reproductive barriers.

Oscine birds preferentially respond to certain sounds over others from an early age, which focuses subsequent learning onto sexually relevant songs.1-3 Songs vary both across species and, due to cultural evolution, among populations of the same species. As a result, early song responses are expected to be shaped by selection both to avoid the fitness costs of cross-species learning4 and to promote learning of population-typical songs.5 These sources of selection are not mutually exclusive but can result in distinct geographic patterns of song responses in juvenile birds: if the risks of interspecific mating are the main driver of early song discrimination, then discrimination should be strongest where closely related species co-occur.4 In contrast, if early discrimination primarily facilitates learning local songs, then it should be tuned to songs typical of the local dialect.5-7 Here, we experimentally assess the drivers of song discrimination in nestling pied flycatchers (Ficedula hypoleuca). We first demonstrate that early discrimination against the songs of the closely related collared flycatcher (F.albicollis) is not strongly affected by co-occurrence. Second, across six European populations, we show that nestlings' early song responses are tuned to their local song dialect and that responses to the songs of collared flycatchers are similarly weak as to those of other conspecific dialects. Taken together, these findings provide clear experimental support for the hypothesis that cultural evolution, in conjunction with associated learning predispositions, drives the emergence of pre-mating reproductive barriers.

Ornaments can evolve to reveal individual quality when their production/maintenance costs make them reliable as `signals¿ or if their expression level is intrinsically linked to condition by some unfalsifiable mechanism (indices). The latter has been mostly associated with traits constrained by body size. In red ketocarotenoid-based colorations, that link could, instead, be established with cell respiration at the inner mitochondrial membrane (IMM). The production mechanism could be independent of resource (yellow carotenoids) availability, thus discarding costs linked to allocation trade-offs. A gene coding for a ketolase enzyme (CYP2J19) responsible for converting dietary yellow carotenoids to red ketocarotenoids has recently been described. We treated male Zebra Finches with an antioxidant designed to penetrate the IMM (mitoTEMPO) and a thyroid hormone (triiodothyronine) with known hypermetabolic effects. Among hormone controls, MitoTEMPO downregulated CYP2J19 in the bill (a red ketocarotenoid-based ornament), supporting the mitochondrial involvement in ketolase function. Both treatments interacted when increasing hormone dosage, indicating that mitochondria and thyroid metabolisms could simultaneously regulate coloration. Moreover, CYP2J19 expression was positively correlated to redness but also to yellow carotenoid levels in the blood. However, treatment effects were not annulated when controlling for blood carotenoid variability, which suggests that costs linked to resource availability could be minor.

Sexual and social selections drive the evolution of conspicuous colorations in many animal species. These traits would function as individual quality signals whether they transmit reliable information. In animal signaling theory, that reliability is guaranteed if those costs of trait production are too expensive for low-quality individuals or, alternatively, assured if the trait expression is inherently linked to individual quality and thus cannot be falsified (“index signals”). A new hypothesis proposes that colored ornaments produced by red keto-carotenoid pigments could act as unfalsifiable index signals similar to other classical examples where quality was ultimately linked to individual body size. These ketocarotenoid pigments are often obtained by enzymatic transformation of dietary yellow carotenoids. Recently, the first enzyme performing this transformation was described: CYP2J19. It belongs to the cytochrome p450 superfamily. It is presumably located in the inner mitochondrial membrane, therefore connecting color expression with cell respiration efficacy. Nevertheless, it is still unknown if the tissue where this cell mechanism acts affects signal honesty and evolution. CYP2J19 expression levels in different species and tissues are currently available. We review current data in avian species and propose that CYP2J19 activity could have evolved by being relocated from the hepatic tissue to the epidermis in those birds where the red color is expressed in non-feathered bare parts. Bare parts require continuous carotenoid mobilization to sustain color. We suggest that tissue-based relocation avoids production costs due to potential CYP2J19 interfering with vital liver functions. Implications for signal reliability in ornamental evolution are discussed.

Extra-pair paternity (EPP) has been broadly reported in socially monogamous bird species and it has been hypothesized that females engage in extra-pair copulations to increase the genetic variability of the offspring and to reduce the risk of inbreeding and genetic incompatibilities. This hypothesis makes two predictions: within populations, females should engage with more dissimilar/heterozygous males and, among popula - tions, females should pursue more frequently EPP in populations characterized by a lower genetic variability and a higher homozygosity. However, support is still unclear throughout literature, and usually involves the study of a single population. We compared a peripheral population of rock sparrow Petronia petronia living at the marginal distribution of the species and characterized by a high EPP level (> 50%) (Italian Alps) with a population located in the centre of the species’ distribution (central Spain), to understand if variations in EPP could be linked to differences in mean heterozygosity and genetic similarity both between and within populations. EPP in the Spanish population was 18.1%, three times lower than that observed in the Alpine one (51.2%), and this difference remained fairly constant across different years. Supporting the between populations prediction, we found lower heterozygosity and reduced allelic richness in the Alpine population compared to the Spanish one. In contrast, social and extra-pair males, as well as within and extra-pair offspring, did not significantly differ in terms of genetic similarity and heterozygosity within brood in either population. Social and extra-pair males did not differ in tarsus size, body weight or yellow badge size, suggesting that females were not choosing extra-pair partners based on heterozygosity, genetic similarity or phenotypic quality. Although based on a limited sample in the within population analysis, our results indicate that EPP may evolve in response to a low level of genetic vari

[Background] The animal signaling theory posits that conspicuous colorations exhibited by many animals have evolved as reliable signals of individual quality. Red carotenoid-based ornaments may depend on enzymatic transformations (oxidation) of dietary yellow carotenoids, which could occur in the inner mitochondrial membrane (IMM). Thus, carotenoid ketolation and cell respiration could share the same biochemical pathways. Accordingly, the level of trait expression (redness) would directly reveal the efficiency of individuals’ metabolism and, hence, the bearer quality in an unfalsifiable way. Different avian studies have described that the flying effort may induce oxidative stress. A redox metabolism modified during the flight could thus influence the carotenoid conversion rate and, ultimately, animal coloration. Here, we aimed to infer the link between red carotenoid-based ornament expression and flight metabolism by increasing flying effort in wild male common crossbills Loxia curvirostra (Linnaeus). In this order, 295 adult males were captured with mist nets in an Iberian population during winter. Approximately half of the birds were experimentally handicapped through wing feather clipping to increase their flying effort, the other half being used as a control group. To stimulate the plumage regrown of a small surface during a short time-lapse, we also plucked the rump feathers from all the birds., [Results] A fraction of the birds with fully grown rump feathers (34 individuals) could be recaptured during the subsequent weeks. We did not detect any significant bias in recovery rates and morphological variables in this reduced subsample. However, among recaptured birds, individuals with experimentally impaired flying capacity showed body mass loss, whereas controls showed a trend to increase their weight. Moreover, clipped males showed redder feathers in the newly regrown rump area compared to controls., [Conclusions] The results suggest that wing-clipped individuals could have endured higher energy expenditure as they lost body mass. Despite the small sample size, the difference in plumage redness between the two experimental groups would support the hypothesis that the flying metabolism may influence the redox enzymatic reactions required for converting yellow dietary carotenoids to red ketocarotenoids.

[EN] In many bird species, physical aggression between males become more frequent during the female’s fertile period, as female encounters with extra-pair males are more frequent and can entail paternity losses. Male aggressiveness during this stage has been proposed as crucial for ensuring male reproductive success. Thus, plumage ornaments could represent honest signals of individual quality that could reflect the aggressiveness of paired territorial males. Furthermore, male aggressiveness could be related to mate quality or defensive capacity. We quantified extra-pair paternity in the broods and investigated the association of male and female traits with the aggressive behaviour of territorial paired males in a Spanish population of Pied Flycatchers (Ficedula hypoleuca), where territorial intrusions were simulated during the female fertile period by placing a taxidermic male mount close to the nest. We predicted that (1) more aggressive males should better protect their mates from intruding males and thereby reduce their paternity losses, (2) males with larger white patches and higher UV reflectance of wing patches should respond more strongly to intrusions, and (3) that males should be more aggressive when mated with higher quality females. We found evidence that males that responded less intensely to a territorial intrusion suffered a higher paternity loss, which offers strong support to the basic tenet of the theory of territoriality as paternity defence. Moreover, both the level of male aggressiveness and control of the territory increased with male UV reflectance of wing patches. Finally, we found, contrary to our prediction, that males were less aggressive when mated with more ornamented females., [GER] Bei vielen Vogelarten nimmt die Häufigkeit physischer Aggression zwischen Männchen während der fertilen Phase der Weibchen zu, wenn Zusammentreffen der Weibchen mit fremden Männchen häufiger sind und zu Vaterschaftsverlusten führen können. Die Aggressivität der Männchen in diesem Stadium gilt als entscheidend für die Sicherung ihres Fortpflanzungserfolgs. Somit könnten Gefiederornamente ehrliche Signale individueller Qualität darstellen, welche die Aggressivität verpaarter Reviermännchen widerspiegeln. Außerdem könnte die männliche Aggressivität in Verbindung mit der Qualität der Partnerin oder den Verteidigungsfähigkeiten stehen. An einer spanischen Population von Trauerschnäppern Ficedula hypoleuca bestimmten wir den Anteil von Fremdvaterschaften an den Bruten und untersuchten den Zusammenhang männlicher und weiblicher Merkmale mit dem Aggressionsverhalten verpaarter Reviermännchen, indem wir während der fertilen Phase der Weibchen durch Platzieren eines präparierten Trauerschnäppermännchens in Nestnähe eine Übertretung der Reviergrenze simulierten. Wir sagten vorher, dass: 1) aggressivere Männchen ihre Partnerinnen besser vor Eindringlingen beschützen und so ihre Vaterschaftsverluste reduzieren; 2) Männchen mit größeren weißen Flecken und stärkerer UV-Reflexion der Flügelfelder stärker auf Eindringlinge reagieren und dass 3) mit Weibchen höherer Qualität verpaarte Männchen aggressiver sind. Wir fanden Belege dafür, dass Männchen, welche schwächer auf eine Überschreitung der Reviergrenze reagierten, höhere Vaterschaftsverluste zu tragen hatten, was eine klare Bestätigung der Grundsatzthese ist, dass Territorialität der Vaterschaftsverteidigung dient. Außerdem nahmen sowohl die männliche Aggressivität als auch die Kontrolle über das Revier in Abhängigkeit von der UV-Reflexion der Flügelfelder bei den Männchen zu. Zu guter Letzt stellte sich entgegen unserer Erwartungen heraus, dass Männchen weniger aggressiv waren, wenn sie mit stärker ornamentierten Weibchen

La teoría evolutiva de la señalización en animales propone que ciertas coloraciones llamativas pueden haber evolucionado para actuar como señales fiables de la calidad del individuo. Las coloraciones rojas producidas por pigmentos carotenoides pueden depender de transformaciones enzimáticas (oxidaciones) de los carotenoides amarillos obtenidos con la dieta, lo cual parece ocurrir dentro de la membrana mitocondrial. De ese modo, la transformación de los pigmentos y la respiración celular (producida en la mitocondria) podrían compartir un mismo mecanismo bioquímico. Tal coincidencia haría que la intensidad de coloración roja reflejara directamente la eficacia metabólica de cada animal y, por tanto, la calidad del mismo de una manera general e infalsificable. Varios trabajos han descrito que el esfuerzo de vuelo puede producir estrés oxidativo. Un metabolismo oxidativo modificado durante el vuelo podría influenciar la transformación de carotenoides y, en último término, la coloración del individuo. Nosotros intentamos inferir la relación entre la expresión de ornamentos pigmentados por carotenoides rojos y el metabolismo del vuelo mediante un experimento en piquituertos comunes (Loxia curvirostra). Se capturaron para ello 295 machos adultos con redes japonesas en una población Ibérica. Esto se hizo durante el invierno ya que es el periodo en el que más piquituertos pueden ser capturados. Aproximadamente, a la mitad de ellos se les recortó dos plumas primarias de cada ala con la intención de aumentar su esfuerzo de vuelo, y la otra mitad fue dejada como control. Para estimular el crecimiento de plumas en una superficie pequeña durante un periodo corto de tiempo y en invierno-primavera, se desplumó un área del obispillo de todas las aves. Durante las siguientes semanas pudimos capturar 34 de estos individuos. No detectamos sesgos en la tasa de recuperación de cada grupo experimental, ni diferencias morfológicas entre ambos. Sin embargo, entre los recapturados, aquellos c