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

Polyphenism in Pogonomyrmex ants: maternal effects and molecular mechanisms underlying caste determination

Phenotypic plasticity, the capacity of a single genome to produce different phenotypes in response to environmental cues, has been a topic of interest for the past decade. Polyphenism is a special case of phenotypic plasticity in which individuals with the same genome exhibit different phenotypes at the same developmental stage. With their reproductive queens and non-reproductive workers, eusocial insects provide one of the best models to study polyphenism, exhibiting a great diversity of morphology, physiology, behavior, and life history. The aim of my thesis is to contribute to the understanding of phenotypic plasticity by investigating two cases of polyphenism in Pogonomyrmex seed harvester ants, the first one on worker size, and the other on the female caste determination (the differentiation into queens and workers). In many ant species, polyphenism is not only found between reproductive queens and non-reproductive workers but also within the worker caste, with the first workers raised in newly founded colonies (nanitics) being much smaller in size than workers raised in mature colonies. In the first chapter, I test whether previously identified miRNAs are involved in the regulation of adult worker size, and more precisely in the development of the nanitic worker phenotype. I experimentally manipulated the levels of the four miRNAs in ant embryos, by injecting a synthetic miRNA, either a mimic or an inhibitor. No difference in size was observed between pupae from the treatment (injection of one synthetic miRNA) and those from the control (injection of water), which strongly suggest that the targeted miRNAs are not involved in worker size. Unexpectedly, I found that the inhibition of one miRNA (miRNA-1) increased the number of larvae developing into gynes. In chapter 2, I investigate the possibility that this miRNA might be involved in caste differentiation. In the following two chapters, I investigated two other instances of caste differentiation: an environmental caste determination using P. rugosus species (chapter 3) and a genetic caste determination using Pogonomyrmex J lineage (chapter 4). In the third chapter, I report evidence that trophic eggs are an evolved maternal adaptation in P. rugosus ants that may regulate caste differentiation. I demonstrate that first instar larvae that consume trophic eggs mostly develop into workers, whereas first instar larvae without trophic eggs mostly develop into gynes, which strongly suggests that trophic eggs influence the larval caste fate. Following this discovery, I investigated the molecular content of these trophic eggs to identify which molecules could induce worker larval development. I found that miRNAs are potential candidates. Finally, in the fourth chapter, I used transcriptomic analysis to investigate the molecular mechanisms underlying gyne and worker caste differentiation in early developmental stages in ants. I found caste-specific gene expression patterns in embryos as early as 24 hours after egg laying, which suggests that caste differentiation starts early in embryonic development in Pogonomyrmex J lineages. Moreover, my results support the idea that the queen phenotype is the default developmental pathway in ants and worker development is a derived pathway that need to be actively switched on. Altogether, this thesis proposes the hypothesis that miRNAs and trophic eggs are two novel factors influencing caste determination in P. rugosus and provides important insights into the understanding of the molecular mechanisms involved in genetic caste determination in ants

Socially transferred materials: why and how to study them

When biological material is transferred from one individual's body to another, as in ejaculate, eggs, and milk, secondary donor-produced molecules are often transferred along with the main cargo, and influence the physiology and fitness of the receiver. Both social and solitary animals exhibit such social transfers at certain life stages. The secondary, bioactive, and transfer-supporting components in socially transferred materials have evolved convergently to the point where they are used in applications across taxa and type of transfer. The composition of these materials is typically highly dynamic and context dependent, and their components drive the physiological and behavioral evolution of many taxa. Our establishment of the concept of socially transferred materials unifies this multidisciplinary topic and will benefit both theory and applications