Yellow, orange, and red coloration is a fundamental aspect of avian diversity and serves as an important signal in mate choice and aggressive interactions. This coloration is often produced through the deposition of diet-derived carotenoid pigments, yet the mechanisms of carotenoid uptake and transport are not wellunderstood. The white recessive breed of the common canary (Serinus canaria), which carries an autosomal recessive mutation that renders its plumage pure white, provides a unique opportunity to investigate mechanisms of carotenoid coloration. We carried out detailed genomic and biochemical analyses comparing the white recessive with yellow and red breeds of canaries. Biochemical analysis revealed that carotenoids are absent or at very low concentrations in feathers and several tissues of white recessive canaries, consistent with a genetic defect in carotenoid uptake. Using a combination of genetic mapping approaches, we show that the white recessive allele is due to a splice donor site mutation in the scavenger receptor B1 (SCARB1; also known as SR-B1) gene. This mutation results in abnormal splicing, with the most abundant transcript lacking exon 4. Through functional assays, we further demonstrate that wild-type SCARB1 promotes cellular uptake of carotenoids but that this function is lost in the predominant mutant isoform in white recessive canaries. Our results indicate that SCARB1 is an essential mediator of the expression of carotenoid-based coloration in birds, and suggest a potential link between visual displays and lipid metabolism.coloration | carotenoids | lipid metabolism | Serinus canaria T he yellow, orange, and red coloration of the feathers, skin, and beaks of birds is most commonly produced through the deposition of carotenoid pigments (1). Carotenoid coloration of birds has been a focus of study in the fields of behavior, evolution, and physiology because it plays a key role in mate assessment in many species. In addition, it is frequently an indicator of individual quality, and can signal species identity (2-4). Birds cannot synthesize carotenoids de novo and must acquire them through their diet (1), potentially linking coloration to the acquisition of pigments from the environment (3). Thus, key hypotheses related to honest signaling and sexual selection have been shaped by and are currently being tested in carotenoidornament systems (5, 6). Ultimately, the information content and evolutionary trajectories of carotenoid ornaments are a function of the physiological mechanisms underlying color expression, yet our understanding of these mechanisms is limited.The expression of carotenoid coloration in birds involves four distinct physiological steps: uptake in the gut, transport in circulatory and lymphatic systems, metabolism either at the site of deposition or in the liver, and deposition in the integument (7). Recent progress has been made in understanding how carotenoids are metabolized to novel forms. In 2016, two studies independently identified a key carotenoid metabolism enzyme,...

Blood parasites may act as modulators of their hosts' ecology, life histories and fitness. We studied the prevalence of Plasmodium sp., Haemoproteus sp. and Leucocytozoon sp. and their effects on morphological, biochemical and haematological variables and on breeding effort of Great Tits Parus major. Total prevalence (percentage of individuals infected by any parasite) ranged from 7.7% to 61.1%. There was an overall positive association in prevalence between the three haematozoan parasites. No effect of sex or age on infection status was observed. Negative impacts of infection on physiological condition depended largely on year and ⁄ or season and included effects on body condition index, plasma protein and haemoglobin index. There were also indications that parasite infection increased immune response and stress levels and activated antioxidant defence mechanisms. Males with higher fledging success had a higher probability of Haemoproteus infection, and females laying heavier eggs had a higher probability of Plasmodium infection. However, clutch size was negatively associated with the probability of infection by Leucocytozoon and Haemoproteus. Surprisingly, males raising second broods had a lower prevalence of both Haemoproteus and Leucocytozoon. Only 5.7% of first-brood nestlings were infected, but those in infected nestboxes had a lower heterophil ⁄ lymphocyte ratio. This study confirms the pathogenicity of blood parasites to the host by demonstrating negative effects of infection on both physiology and breeding performance.

Sexual dichromatism, a difference in coloration between males and females, may be due to sexual selection for ornamentation and mate choice. Here, we show that carotenoid-based dichromatism in mosaic canaries, a hybrid phenotype that arises in offspring of the sexually dichromatic red siskin and monochromatic canaries, is controlled by the gene that encodes the carotenoid-cleaving enzyme β-carotene oxygenase 2 (BCO2). Dichromatism in mosaic canaries is explained by differential carotenoid degradation in the integument, rather than sex-specific variation in physiological functions such as pigment uptake or transport. Transcriptome analyses suggest that carotenoid degradation in the integument might be a common mechanism contributing to sexual dichromatism across finches. These results suggest that differences in ornamental coloration between sexes can evolve through simple molecular mechanisms controlled by genes of major effect.

The consequences of species extinctions in ecological communities may be buffered through the rearrangement (rewiring) of the interactions between the remaining species. The structural and functional consequences of such extinctions can be explored by means of computer simulations that try to predict secondary extinctions and the degradation of ecosystem services. However, to improve the accuracy of these simulations, it is pivotal to evaluate their performance in predicting changes observed in natural communities. In this study, we first described the avian seed dispersal networks in 17 sites throughout Portugal, and found that blackberry (Rubus ulmifolius) was the most dispersed species in 13 out of the 17 sites. Second, we performed a manipulative experiment to evaluate the effect of removing the most dispersed plant species and compared the observed outcome in the structure of the network with computer simulations with and without rewiring. Observed changes were consistent with some rapid network rewiring, with dispersers shifting to alternative fruit species. Although the observed network topology after the

Fruits and seeds are critical food sources for many European passerines during the autumn migration, which in turn contribute to disperse seeds either internally, i.e. after ingestion (endozoochory), or externally, when seeds adhere to the body surface (epizoochory). Despite the recognized importance of birds as seed dispersers, the vast majority of studies focused on endozoochory while the external transport of seeds is frequently invoked as being potentially important, but remains largely unexplored. Th is is particularly important during the post-breeding migration of passerines, the most ubiquitous and diverse movement of potential seed carriers across Europe and into Africa, which coincides with the fruiting peak of many plant species (August -October). Our aim was to evaluate the role of migrating birds as potential long-distance seed dispersers, and comparing the prevalence of epizoochory and endozoochory during post-breeding migration. We sampled 926 wild birds in nine locations in Portugal, and retrieved 1833 seeds of 19 plant species dispersed internally and only three seeds externally attached to three birds ( Serinus serinus , Locustella naevia and Turdus merula ), showing an endozoochory prevalence 85 times higher than that of epizoochory. Migrating and non-migrating passerines dispersed seeds equally. While two of the seeds transported externally had specifi c adaptations to epizoochory, namely spines ( Torilis arvensis ) and hooks ( Galium aparine ), the third is a large seed from a fl eshy-fruited plant, Frangula alnus (i.e. typical endozoochorous syndrome). Th ese seeds were found on bird species with diff erent diets, but similar behaviour (ground foragers) and in similar habitats (open agro-ecosystems). Our results highlight the strong role of migrating passerines as potentially longdistance seed dispersers and show that, at least in the autumn, the prevalence of epizoochory is several orders of magnitude lower than that of endozoochory.

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Birds are hosts for several zoonotic pathogens. Because of their high mobility, especially of longdistance migrants, birds can disperse these pathogens, affecting their distribution and phylogeography. We focused on Borrelia burgdorferi sensu lato, which includes the causative agents of Lyme borreliosis, as an example for tick‐borne pathogens, to address the role of birds as propagation hosts of zoonotic agents at a large geographical scale. We collected ticks from passerine birds in 11 European countries. B. burgdorferi s.l. prevalence in Ixodes spp. was 37% and increased with latitude. The fieldfare Turdus pilaris and the blackbird T. merula carried ticks with the highest Borrelia prevalence (92 and 58%, respectively), whereas robin Erithacus rubecula ticks were the least infected (3.8%). Borrelia garinii was the most prevalent genospecies (61%), followed by B. valaisiana (24%), B. afzelii (9%), B. turdi (5%) and B. lusitaniae (0.5%). A novel Borrelia genospecies “Candidatus Borrelia aligera” was also detected. Multilocus sequence typing (MLST) analysis of B. garinii isolates together with the global collection of B. garinii genotypes obtained from the Borrelia MLST public database revealed that: (a) there was little overlap among genotypes from different continents, (b) there was no geographical structuring within Europe, and (c) there was no evident association pattern detectable among B. garinii genotypes from ticks feeding on birds, questing ticks or human isolates. These findings strengthen the hypothesis that the population structure and evolutionary biology of tick‐borne pathogens are shaped by their host associations and the movement patterns of these hosts.

Discrete colour morphs coexisting within a single population are common in nature. In a broad range of organisms, sympatric colour morphs often display major differences in other traits, including morphology, physiology or behaviour. Despite the repeated occurrence of this phenomenon, our understanding of the genetics that underlie multi-trait differences and the factors that promote the long-term maintenance of phenotypic variability within a freely interbreeding population are incomplete. Here, we investigated the genetic basis of red and black head colour in the Gouldian finch ( Erythrura gouldiae ), a classic polymorphic system in which naturally occurring colour morphs also display differences in aggressivity and reproductive success. We show that the candidate locus is a small (approx. 70 kb) non-coding region mapping to the Z chromosome near the Follistatin ( FST ) gene. Unlike recent findings in other systems where phenotypic morphs are explained by large inversions containing hundreds of genes (so-called supergenes), we did not identify any structural rearrangements between the two haplotypes using linked-read sequencing technology. Nucleotide divergence between the red and black alleles was high when compared to the remainder of the Z chromosome, consistent with their maintenance as balanced polymorphisms over several million years. Our results illustrate how pleiotropic phenotypes can arise from simple genetic variation, probably regulatory in nature.