Acta Universitatis Agriculturae Sueciae Doctoral Thesis No. 2020:44 • No. Thesis Doctoral Acta Universitatis agriculturae Sueciae Doctoral Thesis No. 2020:44 Doctoral Thesis No. 2020:44 Host seeking, which is primarily odour-mediated, is a crucial step of Faculty of Landscape Architecture, Horticulture Chemosensation in mosquito life cycle, and a key determinant of their vectorial capacity. and Crop Production Science The modulation of host seeking relies on several factors, e.g. sex, age, infection by a pathogen, and reflects changes in the expression of chemosensory-related genes. Transcriptome analysis and functional Chemosensation in Aedes aegypti: characterisation of these chemoreceptors have provided a good Aedes aegypti from molecular response profiles to insight into novel control strategies against disease vectors. host-seeking behaviour : from molecular response profiles to host-seeking behaviour profiles molecular response : from Anaïs Karine Tallon completed her graduate education at the Anaïs Karine Tallon Department of Plant Protection Biology at the Swedish University of Agricultural Science (SLU), Alnarp, Sweden. She received her M.Sc. in “Biology, Ecology, Evolution” from the University of Poitiers, France. Acta Universitatis agriculturae Sueciae presents doctoral theses from the Swedish University of Agricultural Sciences (SLU). SLU generates knowledge for the sustainable use of biological natural resources. Research, education, extension, as well as environmental monitoring and assessment are used to achieve this goal. • Anaïs Karine Tallon Karine Anaïs • Online publication of thesis summary: https://pub.epsilon.slu.se ISSN 1652-6880 ISBN (print version) 978-91-7760-606-2 ISBN (electronic version) 978-91-7760-607-9 Chemosensation in Aedes aegypti: from molecular response profiles to host-seeking behaviour Anaïs Karine Tallon Faculty of Landscape Architecture, Horticulture and Crop Production Science Department of Plant Protection Biology Alnarp Doctoral thesis Swedish University of Agricultural Sciences Alnarp 2020 Acta Universitatis agriculturae Sueciae 2020 :44 Cover: Painting by F. Dezozier and A. Tallon (photo: A. Tallon) ISSN 1652-6880 ISBN (print version) 978-91-7760-606-2 ISBN (electronic version) 978-91-7760-607-9 © 2020 Anaïs Karine Tallon, Swedish University of Agricultural Sciences Alnarp Print: SLU Service/Repro, Alnarp 2020 Chemosensation in Aedes aegypti: from molecular response profiles to host-seeking behaviour Abstract The female mosquito Aedes aegypti is the primary urban vector of various highly infectious neglected tropical diseases. Disease transmission relies heavily on odour- mediated behaviours, including e.g., sugar- and host-seeking, which are crucial during the mosquito life cycle and has dire impacts on vectorial capacity. Olfaction is, one of the most sophisticated sensory systems, and is the sense by which insects locate and discriminate biologically-relevant odorant volatiles. In female mosquitoes, host-seeking is generally not observed before 2-3 days following adult emergence. Of note, males have also been shown to respond to and orient towards host-associated cues. Vector-borne pathogens can alter the behaviour and physiology of their host, consequently increasing the risk of disease transmission. Thus, the modulation of host-seeking depends on multiple factors, including e.g., age, sex, and infection by a pathogen, which is the main focus of this thesis. During my PhD, I have shown that the modulation of the onset of host-seeking coincides with changes in transcript abundance of chemosensory-related genes expressed in the antennae of newly-emerged mosquitoes. Of these genes, one particular odorant receptor, OR117, exhibits a decrease in transcript abundance as female mosquitoes become capable of host-seeking. Later, I have functionally characterised OR117, together with another odorant receptor-of-interest, OR103, which has previously been shown to be more abundant in the human-preferring subspecies of Ae. aegypti. Both OR117 and OR03 are tuned to monoterpenes, and their potential role in the transition between sugar- to host-seeking and human avoidance, respectively, is discussed. Furthermore, I have demonstrated that the locomotion and host-seeking is modulated in dengue-infected females in a time-dependent manner, i.e. depending on the time post-infection, and coincides with changes in transcript abundance of genes involved in neural signalling pathways. A better understanding of the modulation of odour-mediated behaviours in mosquitoes is crucial for the development of efficient control strategies against disease vector control. Keywords: chemical ecology, chemosensory-related genes, dengue, deorphanization, electrophysiology, heterologous expression, mosquitoes, olfaction Author’s address: Anaïs Karine Tallon, Swedish University of Agricultural Sciences, Department of Plant Protection Biology, Alnarp, Sweden Dedication To the next generations of PhD students… you are not alone. “All in all it’s just another brick in the wall” (Roger Waters) And to you, reader, for keeping this thesis alive. “Do not judge me by my success, judge me by how many times I fell down and got back up again” (Nelson Mandela) Contents List of publications ......................................................................... 10 Abbreviations ................................................................................ 14 1 Introduction .......................................................................... 17 Box 1. Aedes aegypti ............................................................................. 18 2 The implication of olfaction on the vectorial capacity of mosquitoes .................................................................................... 21 2.1 Sugar seeking ............................................................................. 21 2.1.1 Relevant life-history traits affected by sugar feeding ...... 21 2.1.2 Environmental factors regulating sugar seeking ............. 23 2.1.3 Onset of sugar seeking and tendency to sugar feed ..... 25 2.1.4 The dynamic interplay between sugar- and host- seeking………………………………………………………………..26 2.2 Chemical ecology of sugar seeking ............................................ 28 2.2.1 Host plant selection ........................................................ 28 2.2.2 Odour-based host plant discrimination ........................... 30 2.2.3 Control of vector populations: emphasis on sugar bait stations ........................................................................................ 31 2.3 Host-seeking ............................................................................... 33 2.3.1 Onset of female host-seeking and importance of blood feeding ....................................................................................... 33 2.3.2 Regulation of host-seeking during the first gonotrophic cycle …………………………………………………………………..34 2.3.3 Host-seeking in male mosquitoes, an often-neglected sex ……………………………………………………………………36 2.3.4 Divergence of host selection ....………..………………….37 2.3.5 Modulation of host-seeking by pathogen infection………………………………………………………….……39 2.4 Chemical ecology of host-seeking .............................................. 41 2.4.1 The role of semiochemicals in host-seeking ................... 41 2.4.2 Host volatiles and attractants ......................................... 43 2.4.3 Inter-individual variation in human attractiveness ........... 45 Box 2. Dengue, currently the most rapidly spreading vector-borne disease in the world…………………………………………………48 Box 3. Other neglected tropical diseases transmitted by Ae. aegypti………………………………………………………………..51 3 Mosquito peripheral olfactory system ................................... 54 3.1 Peripheral olfactory organs ......................................................... 54 3.1.1 Main olfactory organ - the antenna ................................. 55 3.1.2 Other olfactory appendages ........................................... 56 3.1.3 Chemosensory sensilla .................................................. 57 3.2 Chemosensory binding proteins ................................................. 59 3.2.1 OBPs .............................................................................. 60 3.2.2 CSPs............................................................................... 62 3.3 Chemosensory receptors ............................................................ 63 3.3.1 ORs................................................................................. 64 3.3.2 GRs................................................................................. 66 3.3.3 IRs .................................................................................. 68 3.2.3 SNMPs............................................................................ 69 3.2.4 ODEs .............................................................................. 70 3.4 Non-canonical chemosensory receptors .................................... 71 1.2.1 TRPs ............................................................................... 71 1.2.2 PPKs ............................................................................... 73 4 Molecular basis of olfaction .................................................. 76 4.1 Pheripheral coding of odorant signals ......................................... 76 4.1.1 Detecting and encoding odours ...................................... 76 4.1.2 Combinatorial coding versus labelled lines .................... 79 4.2 Regulation of chemosensory gene expression