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- Fors, Lisa, 1976-
(author)
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Ecology and evolution in a host-parasitoid system : Host search, immune responses and parasitoid virulence
- 2015
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
- Fors, Lisa, 1976-
(author)
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Interactions and Coevolution in Tritrophic systems
- 2012
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Reports (other academic/artistic)abstract
- Ecological systems are usually complex, with a number of interacting species. These species interactions are commonly divided into two major groups: mutualistic and antagonistic. If the interactions are mutualistic, they are beneficial for all species involved, as in specialized relationships between certain plants and their pollinators. Antagonistic interactions, on the other hand, can be either competitive or trophic. Trophically interacting species are for example plants and their associated herbivores, predators and their prey or parasites and their hosts. In many of these interactions, some species are depending on others in order to survive. If one species changes, other species associated to it may have to adapt to the changes. This may lead to a process of reciprocal evolution between the interacting species, called coevolution. In this paper I start with a brief background on coevolution and local adaptation, and then describe some interactions in tritrophic systems. The tritrophic systems I focus on consist of plants, herbivore insects and parasitoids. I discuss some processes and mechanisms in these systems, such as host search, plant defense and the immune response in insects. In the end of the paper, a short description of my PhD-project is included.
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