A Comprehensive Study of the Avian Preen Wax’ Adaptive Role in Feather Microbial Ecology

Organisms employ diverse adaptive strategies to ensure their protection against environmental microorganisms. Birds, in addition to other strategies common to vertebrates, stand out with two specific integumentary adaptations: feathers and the preen gland. Feathers, crucial for flight, insulation, camouflage and communication, not only benefit from structural protection but are also coated with preen wax, an oily substance produced by the preen gland, and host communities of beneficial (yet potentially pathogenic) microorganisms known as feather microbiota. Considering the negative impact of insufficient feather protection, our study combined lipidomic and proteomic analyses and high-throughput 16S rRNA gene sequencing to investigate the role of both preen gland and feather microbiota in protecting barn owl (Tyto alba) plumage during reproduction. In the first two chapters, we explored the influence of individual (sex, body condition, plumage coloration) and environmental (weather conditions, brood size) factors on preen gland and feather microbiota. Our results revealed that incubating females secreted more preen wax and exhibited lower feather bacterial diversity compared to rearing females and males. Increasing preen wax secretion may have indirectly reduced feather bacterial diversity in incubating females. However, no direct association was observed between preen wax amount and feather bacterial diversity or composition in the second chapter. In the third chapter, we explored the influence of preen wax’ lipid composition on feather microbiota, and contrary to the previous chapter, our results revealed a slight association between preen wax (lipid) composition and feather bacterial composition. This slight association prompted our exploration of preen wax’ proteomic composition in the fourth chapter, whose results revealed the presence of immune- related peptides and proteins in barn owl preen wax. This thesis enhances our understanding of preen gland’s complex functioning in birds. Not only does it partly support the protective function of preen gland but also suggests its involvement in other functions such as signaling and communication. -- Les organismes emploient diverses stratégies adaptatives pour se protéger contre les microorganismes environnementaux. Les oiseaux, en plus d’autres stratégies communes aux vertébrés, se distinguent par deux adaptations tégumentaires spécifiques : les plumes et la glande uropygienne. Les plumes, essentielles pour le vol, l’isolation thermique, le camouflage et la communication, bénéficient non seulement d’une protection structurelle mais sont également recouvertes de cire uropygienne, une substance huileuse produite par la glande uropygienne, et hébergent des communautés de microorganismes bénéfiques (mais aussi pathogènes) connues sous le nom de microbiote des plumes. Compte tenu de l’impact négatif d’une protection insuffisante du plumage sur les oiseaux, notre étude a combiné des analyses lipidomiques et protéomiques ainsi que du séquençage à haut débit de l’ARNr 16S pour étudier le rôle de la glande uropygienne et du microbiote des plumes dans la protection du plumage de l’Effraie des clochers (Tyto alba) pendant la reproduction. Dans les deux premiers chapitres, nous avons exploré l’influence de facteurs individuels (sexe, condition physique, coloration du plumage) et environnementaux (conditions météo, taille de la nichée) sur la glande uropygienne et le microbiote des plumes. Nos résultats ont révélé que les femelles incubatrices sécrétaient davantage de cire uropygienne et présentaient une diversité bactérienne du plumage moindre par rapport aux autres femelles et aux mâles. Cette sécrétion accrue de cire uropygienne pourrait avoir indirectement contribué à la réduction de la diversité bactérienne du plumage chez les femelles incubatrices. Cependant, nous n’avons pas observé d’association directe entre la quantité de cire uropygienne et la diversité ou la composition bactérienne du plumage dans le deuxième chapitre. Dans le troisième chapitre, nous avons exploré l’influence de la composition lipidique de la cire uropygienne sur le microbiote des plumes, et contrairement au chapitre précédent, nos résultats ont révélé une légère association entre la composition lipidique de la cire uropygienne et la composition bactérienne du plumage. Cette légère association nous a incités à explorer la composition protéomique de la cire uropygienne dans le quatrième chapitre, dont les résultats ont révélé la présence de peptides et protéines liés au système immunitaire dans la cire uropygienne de l’Effraie des clochers. Cette thèse améliore ainsi notre compréhension du fonctionnement complexe de la glande uropygienne chez les oiseaux. Elle soutient non seulement partiellement la fonction protectrice de la glande uropygienne, mais suggère également son implication dans d’autres fonctions telles que la communication

Genetic compatibility exceeds possible ‘good genes’ effects of sexual selection in lake char

Mating is rarely random in nature, but the effects of mate choice on offspring performance are still poorly understood. We sampled in total 47 wild lake char (Salvelinus umbla) during two breeding seasons and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, 1,464 embryos that resulted from sperm competition trials were raised singly in either a stress- or non-stress environment. Offspring growth turned out to be strongly reduced with increased genetic relatedness between the parents while male coloration (that reveal aspects of male health) was no significant predictor of offspring performance. In a second experiment one year later, block-wise full-factorial in vitro breeding was used to produce 3,094 embryos that were raised singly after sublethal exposures to a pathogen or water only. Offspring growth was again strongly reduced with increased genetic relatedness between the parents while male coloration was no significant predictor of offspring performance. We conclude that the genetic benefits of mate choice would be strongest if females avoided genetic similarity, while male breeding colors seem more relevant in intra-sexual selection

Host conservation through their parasites: molecular surveillance of vector-borne microorganisms in bats using ectoparasitic bat flies

Most vertebrates host a wide variety of haematophagous parasites, which may play an important role in the transmission of vector-borne microorganisms to hosts. Surveillance is usually performed by collecting blood and/or tissue samples from vertebrate hosts. There are multiple methods to obtain samples, which can be stored for decades if properly kept. However, blood sampling is considered an invasive method and may possibly be harmful to the sampled individual. In this study, we investigated the use of ectoparasites as a tool to acquire molecular information about the presence and diversity of infectious microorganism in host populations. We tested the presence of three distinct vector-borne microorganisms in both bat blood and bat flies: Bartonella bacteria, malaria-like Polychromophilus sp. (Apicomplexa), and Trypanosoma sp. (Kinetoplastea). We detected the presence of these microorganisms both in bats and in their bat flies, with the exception of Trypanosoma sp. in South African bat flies. Additionally, we found Bartonella sp. in bat flies from one population in Spain, suggesting its presence in the host population even if not detected in bats. Bartonella and Polychromophilus infection showed the highest prevalence in both bat and bat fly populations. Single, co- and triple infections were also frequently present in both. We highlight the use of haematophagous ectoparasites to study the presence of infectious microorganism in host blood and its use as an alternative, less invasive sampling method

Sex-Specific Stress Tolerance in Embryos of Lake Char (Salvelinus umbla)

Salmonid fish have become important models in evolution and ecology, but possible effects of embryo or larval sex are mostly ignored, probably because morphological gonad formation starts only months after hatching and sexual maturation years later. However, recent gene expression studies and first observations in domestic strains suggest that sex-specific life histories could already start at an embryonic stage. Here we test this hypothesis in embryos and larvae of lake char (Salvelinus umbla). We sampled wild char and used their gametes to produce embryos of 40 different families. Embryos were raised singly in a stress or a non-stress environment until a late larval stage (stress was induced by allowing remainders of ovarian fluids to support microbial growth). Genetic markers were then used to sex the fish and reconstruct paternity (N = 1,463, including dead embryos). Primary sex ratio did not differ among families and was about 1:1. Female embryos hatched on average later and showed lower stress tolerance than male embryos. There were significant parental effects on offspring growth and mortality, but the sex differences in embryo performance were not family specific. We conclude that the sexes differ in their life history and susceptibilities to environmental stress already at embryonic stages. Environmental stress during incubation can therefore affect population sex ratio and hence population growth and genetics

Genomic compatibility excels possible ‘good genes’ effects of sexual selection in lake char

Mating is rarely random in nature, but the effects of mate selection on offspring performance are still poorly understood, even in well-established models such as salmonid fish. We sampled wild lake char (Salvelinus umbla) and used their gametes to investigate the genetic consequences of different mating scenarios. In a first study, we used full-factorial breeding to experimentally separate additive genetic from maternal environmental effects. This led to 60 families and in total 1,073 embryos that were raised singly after sublethal exposures to the pathogen Aeromonas salmonicida, the common pollutant ethinylestradiol, or water only. Contrary to predictions of ‘good genes’ sexual selection, offspring of more yellow males were less tolerant to the pathogen than offspring of pale males, while male coloration did not predict offspring tolerance to ethinylestradiol. However, increased kinship between the parents had strong negative effects on embryo development in all treatment groups. In a second experiment, we monitored 1,464 singly-raised embryos that resulted from 70 pair-wise sperm competition trials. These embryos were raised in an environment that supports the growth of symbiotic microbes (sublethal stress) or in a clean environment. Offspring of yellow males were again less stress tolerant than those of pale males, and embryo development was again slowed down with increasing genetic similarity between the parents. We conclude that genetic benefits of mate selection would be strongest if females avoided genetic similarity during mate selection, for example based on MHC-linked signals, while male breeding colors seem more relevant in intra-sexual selection