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Geographic variation in hemocyte diversity and phagocytic propensity shows a diffuse genomic signature in the green veined white butterfly
Stockholm University, Faculty of Science, Department of Zoology, Population Genetics.ORCID iD: 0000-0002-8782-3477
Stockholm University, Faculty of Science, Department of Zoology, Population Genetics.ORCID iD: 0000-0002-7796-7987
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.ORCID iD: 0000-0001-9643-5874
Stockholm University, Faculty of Science, Department of Molecular Biosciences, The Wenner-Gren Institute.ORCID iD: 0000-0003-3964-9512
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Insects rely on their innate immune system to successfully mediate complex interactions with their internal microbiota, as well as the microbes present in the environment. Given the variation in microbes across habitats, the challenges to respond to them is likely to result in local adaptation in the immune system. Here we focus upon phagocytosis, a mechanism by which pathogens and foreign particles are engulfed in order to be contained, killed and processed for antigen presentation. We investigated the phenotypic and genetic variation related to phagocytosis, in two allopatric populations of the butterfly Pieris napi. We found that the populations differ in their hemocyte composition, and overall phagocytic capability, driven by the increased phagocytic propensity of each cell type. However, no evidence for divergence in phagocytosis-related genes was observed, though an enrichment of genes involved in glutamine metabolism was found, which have recently been linked to immune cell differentiation in mammals.

National Category
Evolutionary Biology
Research subject
Population Genetics
Identifiers
URN: urn:nbn:se:su:diva-175463DOI: 10.1101/790782OAI: oai:DiVA.org:su-175463DiVA, id: diva2:1366240
Available from: 2019-10-28 Created: 2019-10-28 Last updated: 2019-11-01Bibliographically approved
In thesis
1. Immunity & the butterfly: A functional genomic study of natural variation in immunity
Open this publication in new window or tab >>Immunity & the butterfly: A functional genomic study of natural variation in immunity
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Butterflies are ubiquitous and abundant, occurring in a wide variety of environments that contain diverse microbial communities with varied pathogenic pressures. These pathogens and parasites present a constant threat to organisms, and have led to the evolution of complex and intricate immune responses. Despite strong selection against immunological threats, organisms display great variation in their immune capabilities, both on the genetic and physiological level. Investigating this variation remains challenging, since differences in immune responses might arise from changes in the amount, size or performance of cells or organs. Disentangling these relative contributions is important, as the targets of selection are expected to differ, ranging from immune genes directly related to the phenotype to genes indirectly involved via cell proliferation. This thesis focuses on characterizing the immune system of the butterfly Pieris napi and investigating its remarkable variation across populations by using both phenotypic and genotypic measurements. By integrating RNA-seq with life history measurements, I found that the cost of infection and wounding in the final larval stage carries over the metamorphic boundary in P. napi (Paper II). Using population comparisons, I identified both the action and potential targets of natural selection in wild populations within their respective immune responses (Paper I, III & IV). The immune genes in P. napi show increased genetic variation compared to the rest of the genome, and microevolutionary selection dynamics act on these genes between and among populations (Paper I). I measured the cellular immune responses related to phagocytosis and melanization in common garden reared larvae originating from two allopatric populations (Spain, Sweden) (Paper III & IV). The two populations were found to differ in their blood cell composition, and overall phagocytic capability, driven by the increased phagocytic propensity of each cell type (Paper III). However, genome wide analysis of divergence between these populations found no excess genetic differentiation in genes annotated to phagocytic capacity, suggesting that our observed population differences might arise from genes affecting the activation or transdifferentiation of cells, which currently lack functional annotation. Interestingly, genes involved in glutamine metabolism, which have been linked to immune cell differentiation in mammals, did show divergence between the populations. In addition, the populations also differed in prophenoloxidase activity, a common method for quantifying immune related melanization in insects, along with the abundance of the cell-type (oenocytoids) related to this important immune function (Paper IV). Integrative analysis using both transcriptomic and genomic data revealed that the genes involved in this phenotype showed no significant differentiation between the populations. However, a gene involved with proper trafficking of melanogenic enzymes in vertebrates was found to be highly expressed and highly diverged between the two populations, providing an interesting candidate for future studies. This thesis demonstrates the advantages of integrating several genomic tools with lab experiments to quantify natural variation in the immune system of butterflies.

 

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm, 2019. p. 31
Keywords
eco-immunology, functional genomics, transcriptomics, innate immunity, selection dynamics, melanization, phagocytosis, population genetics, Pieris napi
National Category
Evolutionary Biology Genetics Zoology
Research subject
Population Genetics
Identifiers
urn:nbn:se:su:diva-175465 (URN)978-91-7797-825-1 (ISBN)978-91-7797-826-8 (ISBN)
Public defence
2019-12-13, Vivi Täckholmsalen (Q-salen), NPQ-huset, Svante Arrhenius väg 20, Stockholm, 10:00 (English)
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Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2019-11-20 Created: 2019-10-28 Last updated: 2019-11-11Bibliographically approved

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Keehnen, NaomiFors, LisaJärver, PeterSpetz, Anna-LenaNylin, SörenTheopold, UlrichWheat, Christopher
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