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Ecology and evolution in a host-parasitoid system: Host search, immune responses and parasitoid virulence
Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In host-parasitoid systems, there is a continuous coevolutionary arms race where each species imposes a strong selection pressure on the other. The host needs to develop defence strategies in order to escape parasitism and the parasitoid must evolve counter-defence strategies in order to overcome the host’s immune defence and successfully reproduce. This makes host-parasitoid systems excellent model systems for understanding evolutionary processes underlying host race formation and speciation. In order to gain a better understanding of the complexity of host-parasitoid interactions several aspects must be considered, such as search behaviour and host selection in the parasitoid, the development of immune responses in the host and counter-defence strategies in the parasitoid. In this thesis, I investigate interactions and coevolution in a natural host-parasitoid system, consisting of five species of Galerucella leaf beetles and three species of Asecodes parasitoids, by combining behavioural ecology with chemical ecology and immunology. In the studies performed, I found that pheromone production and responses in the beetles are connected to the phylogenetic relatedness between the Galerucella species (Paper I). I found no evidence that Asecodes exploits the adult pheromone to locate host larvae, but observed an ability in the parasitoids to distinguish a better host from a less suitable one based on larval odors (Paper II). The studies also revealed large differences in immune competence between the Galerucella species, which were linked to differences in hemocyte composition in the beetle larvae (Paper III, IV). Further, the results suggest that parasitism success in polyphagous Asecodes is strongly affected by former host species of the parasitoid (Paper IV). In conclusion, the results of this thesis suggest an on-going evolution in both parasitoid virulence and host immune responses in the Asecodes-Galerucella system.

Place, publisher, year, edition, pages
Stockholm: Department of Ecology, Environment and Plant Sciences, Stockholm University , 2015. , 44 p.
Keyword [en]
Host-parasitoid interactions, Plant-herbivore interactions, Host search, Volatiles, Pheromones, Geographic variation, Cellular defence, Melanisation, Encapsulation, Asecodes, Galerucella
National Category
Ecology Immunology
Research subject
Plant Ecology
Identifiers
URN: urn:nbn:se:su:diva-115243ISBN: 978-91-7649-103-4 (print)OAI: oai:DiVA.org:su-115243DiVA: diva2:796763
Public defence
2015-05-08, föreläsningssalen, Institutionen för ekologi, miljö och botanik, Lilla Frescativägen 5, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

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

Available from: 2015-04-16 Created: 2015-03-18 Last updated: 2015-04-17Bibliographically approved
List of papers
1. Chemical communication and host search in Galerucella leaf beetles
Open this publication in new window or tab >>Chemical communication and host search in Galerucella leaf beetles
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2015 (English)In: Chemoecology, ISSN 0937-7409, E-ISSN 1423-0445, Vol. 25, no 1, 33-45 p.Article in journal (Refereed) Published
Abstract [en]

Herbivore insects use a variety of search cues during host finding and mate recognition, including visual, gustatory, and olfactory stimuli, leaving multiple traits for evolution to act upon. However, information about differences or similarities in search pattern amongst closely related insect herbivore species is still scarce. Here, we study the production of and the response to pheromone in Galerucella (Coleoptera: Chrysomelidae) to investigate the beetles' search behaviour. Males of G. pusilla and G. calmariensis, two closely related species, are known to produce the aggregation pheromone dimethylfuran-lactone when feeding on their host plant, whereas no pheromones have been identified in other Galerucella species. We show that dimethylfuran-lactone is produced also by males of G. tenella, a species phylogenetically close to G. pusilla and G. calmariensis, whereas the more distantly related species G. lineola and G. sagittariae were not found to produce the same compound. To investigate the beetles' behavioural response to dimethylfuran-lactone, the pheromone was synthesized using a partly novel method and tested in olfactometers, showing that G. pusilla, G. calmariensis, and G. tenella were all attracted to the pheromone, whereas G. lineola and G. sagittariae did not respond. This suggests that the production of and the response to pheromone could be linked to the phylogenetic relatedness between the species.

Keyword
Pheromone, Volatiles, Plant-herbivore interactions, Olfactometer
National Category
Biological Sciences Earth and Related Environmental Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-114227 (URN)10.1007/s00049-014-0174-1 (DOI)000348147000004 ()
Note

AuthorCount:7;

Available from: 2015-03-19 Created: 2015-02-25 Last updated: 2017-12-04Bibliographically approved
2. Host search and host preference in Asecodes parviclava
Open this publication in new window or tab >>Host search and host preference in Asecodes parviclava
(English)Manuscript (preprint) (Other academic)
National Category
Ecology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-115185 (URN)
Available from: 2015-03-17 Created: 2015-03-17 Last updated: 2016-01-29Bibliographically approved
3. Differences in Cellular Immune Competence Explain Parasitoid Resistance for Two Coleopteran Species
Open this publication in new window or tab >>Differences in Cellular Immune Competence Explain Parasitoid Resistance for Two Coleopteran Species
2014 (English)In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 9, e108795Article in journal (Refereed) Published
Abstract [en]

The immune defence of an organism is evolving continuously, causing counteradaptations in interacting species, which in turn affect other ecological and evolutionary processes. Until recently comparative studies of species interactions and immunity, combining information from both ecological and immunological fields, have been rare. The cellular immune defense in insects, mainly mediated by circulating hemocytes, has been studied primarily in Lepidoptera and Diptera, whereas corresponding information about coleopteran species is still scarce. In the study presented here, we used two closely related chrysomelids, Galerucella pusilla and G. calmariensis (Coleoptera), both attacked by the same parasitoid, Asecodes parviclava (Hymenoptera). In order to investigate the structure of the immune system in Galerucella and to detect possible differences between the two species, we combined ecological studies with controlled parasitism experiments, followed by an investigation of the cell composition in the larval hemolymph. We found a striking difference in parasitism rate between the species, as well as in the level of successful immune response (i.e. encapsulation and melanisation of parasitoid eggs), with G. pusilla showing a much more potent immune defense than G. calmariensis. These differences were linked to differences in the larval cell composition, where hemocyte subsets in both naive and parasitised individuals differed significantly between the species. In particular, the hemocytes shown to be active in the encapsulation process; phagocytes, lamellocytes and granulocytes, differ between the species, indicating that the cell composition reflects the ability to defend against the parasitoid.

National Category
Biological Sciences
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-108717 (URN)10.1371/journal.pone.0108795 (DOI)000342685600102 ()
Note

AuthorCount:4;

Available from: 2014-11-05 Created: 2014-11-03 Last updated: 2017-12-05Bibliographically approved
4. Geographic variation in parasitoid virulence and parasitoid host race formation
Open this publication in new window or tab >>Geographic variation in parasitoid virulence and parasitoid host race formation
(English)Manuscript (preprint) (Other academic)
National Category
Ecology Immunology
Research subject
Plant Ecology
Identifiers
urn:nbn:se:su:diva-115186 (URN)
Available from: 2015-03-17 Created: 2015-03-17 Last updated: 2016-01-29Bibliographically approved

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