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Peter HambäckProfessor


  • Coevolution in host-parasitoid systems
  • Ecological immunology
  • The ecological role of gut microbiomes
  • Wetlandscape ecology
  • Spider ecology
  • Genomic tools for diet analysis

Research projects

  • The ecology and evolution of indirect interactions in host-parasitoid systems. People involved: Xuyue Yang (SU), Ulrich Theopold (SU), Chris Wheat (SU), Tanja Slotte (SU). Financed through the Swedish Research Council Vetenskapsrådet.
  • Managing constructed and natural wetlands for arthropod diversity in agricultural landscapes. Financed through the Swedish Research Council Formas and through the Swedish Environmental Protection Agency (Naturvårdsverket). Main collaborators include David Åhlén, John Strand (Hushållningssällskapet) and Jerker Jarsjö (SU). For more information see
  • Transferability of gut microbiomes and the ecology of plant-herbivore-parasitoid interactions. People involved: Yueqing An (SU), Chris Wheat (SU), Sarahi García (SU). Financed through the Swedish Research Council Vetenskapsrådet.

PhD-students (current and previous)


Xuyue Yang, "Coevolution and molecular background of species interactions in geographic mosaics"

David Åhlén, "Managing constructed and natural wetlands for arthropod diversity in agricultural landscapes"

Yueqing An, "Transferability of gut microbiomes and the ecology of plant-herbivore-parasitoid interactions"


Thomas Verschut (main advisor), Dissertation 2017-06-02 on “Searching for food in complex environments: Integrating processes at multiple spatial scales”.

Alma Strandmark (main advisor), Dissertation 2017-06-09, on “Effects of climate induced sea-level changes on coastal ecosystems: plants and arthropods”.

Ulrika Samnegård (coadvisor, main advisor: Kristoffer Hylander), Dissertation 2016-04-01, on "Ecosystem services and disservices on home grown coffee along land-use gradients in Ethiopia: pollination and pest damage"

Lisa Fors, Dissertation 2015-05-08, on “Coevolution in a tritrophic systems: from purple loosestrife to natural enemies"

Lina Lehndal (coadvisor, main advisor: Jon Ågren), Dissertation 2015-05-08, on “Effects of herbivory on population dynamics and evolution of resistance in purple loosestrife (Lythrum salicaria L.)”

Debissa Lemessa (coadvisor, main advisor: Kristoffer Hylander), Dissertation 2014-06-05, on “Pests and pest controlling organisms across tropical agroecological land-scapes in relation to forest and tree cover”.

Petter Andersson (main advisor), Dissertation: 2011-10-27, on “The importance of search behavior for spatial distributions of herbivorous insects”

Gundula Kolb (main advisor), Dissertation: 2010-11-05, on “The impact of cormorant nesting colonies on plants and arthropods“

Kajsa Mellbrand (main advisor), Dissertation: 2009-06-05, on “The Spider and the Sea: Effects of marine subsidies on the role of spiders in terrestrial food webs“

Hannah Östergård (coadvisor, main advisor: Johan Ehrlén), Dissertation: 2008-05-30, on “Plant-seed predator interactions – ecological and evolutionary aspects”

Maria Björkman (coadvisor, main advisor: Birgitta Rämert), Dissertation: 2007-12-13, on “Effects of intercropping on the life cycle of the turnip root fly (Delia floralis)”


I urval från Stockholms universitets publikationsdatabas

  • Geographic variation and trade-offs in parasitoid virulence

    2016. Lisa Fors (et al.). Journal of Animal Ecology 85 (6), 1595-1604


    1. Host-parasitoid systems are characterized by a continuous development of new defence strategies in hosts and counter-defence mechanisms in parasitoids. This co-evolutionary arms race makes host-parasitoid systems excellent for understanding trade-offs in host use caused by evolutionary changes in host immune responses and parasitoid virulence. However, knowledge obtained from natural host-parasitoid systems on such trade-offs is still limited.

    2. In this study, the aim was to examine trade-offs in parasitoid virulence in Asecodes parviclava (Hymenoptera: Eulophidae) when attacking three closely related beetles: Galerucella pusilla, Galerucella calmariensis and Galerucella tenella (Coleoptera: Chrysomelidae). A second aim was to examine whether geographic variation in parasitoid infectivity or host immune response could explain differences in parasitism rate between northern and southern sites.

    3. More specifically, we wanted to examine whether the capacity to infect host larvae differed depending on the previous host species of the parasitoids and if such differences were connected to differences in the induction of host immune systems. This was achieved by combining controlled parasitism experiments with cytological studies of infected larvae.

    4. Our results reveal that parasitism success in A. parviclava differs both depending on previous and current host species, with a higher virulence when attacking larvae of the same species as the previous host. Virulence was in general high for parasitoids from G. pusilla and low for parasitoids from G. calmariensis. At the same time, G. pusilla larvae had the strongest immune response and G. calmariensis the weakest. These observations were linked to changes in the larval hemocyte composition, showing changes in cell types important for the encapsulation process in individuals infected by more or less virulent parasitoids.

    5. These findings suggest ongoing evolution in parasitoid virulence and host immune response, making the system a strong candidate for further studies on host race formation and speciation.

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  • Disentangling associational effects

    2016. Thomas A. Verschut (et al.). Functional Ecology 30 (11), 1826-1833


    Neighbouring resources have been found to either decrease or increase the likelihood that a consumer organism attacks a focal resource. These phenomena are referred to as associational resistance (AR) and associational susceptibility (AS), respectively. While associational effects have been observed in various field studies, little is known on how resource heterogeneity can cause associational effects. We used a laboratory approach in which we studied the effects of resource density and frequency in the search behaviour of Drosophila melanogaster as a model organism for olfactory-guided behaviour in insects. We first determined whether D.melanogaster could discriminate between odour sources that differ quantitatively. Secondly, we determined what the effect of resource density and frequency was on the search behaviour of D.melanogaster by combining these resources into various patch arrangements. Finally, we used the outcome of our experiments to disentangle the role of resource density and frequency in associational effects. We found that D.melanogaster has the ability to discriminate between quantitatively different resources, but that the attraction to resource density is constrained by an optimum after which attraction decreases. Furthermore, in heterogeneous environments, flies showed a strong preference towards the more apparent resource, leading to AS for the more apparent resources and AR for the less apparent resource. The strength of this interaction increased with a decreasing frequency of the more apparent resource. These results imply that D.melanogaster mainly selects patches at the level of individual resources. Consequently, when a patch contains qualitatively different resources, the more apparent resource will attract a higher number of flies than the less apparent resource irrespective of the frequency of the apparent resource within the patch. Our study shows that associational effects can be explained by determining the hierarchical level at which a consumer selects its resources. When a consumer selects resources at the individual level rather than at the patch level, our results can be used to explain the population dynamics of host plants and their associated consumers under field conditions.

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  • Differential Expression of Immune Genes between Two Closely Related Beetle Species with Different Immunocompetence following Attack by Asecodes parvidava

    2020. Xuyue Yang (et al.). Genome Biology and Evolution 12 (5), 522-534


    Endoparasitoid wasps are important natural enemies of many insect species and are major selective forces on the host immune system. Despite increased interest in insect antiparasitoid immunity, there is sparse information on the evolutionary dynamics of biological pathways and gene regulation involved in host immune defense outside Drosophila species. We de novo assembled transcriptomes from two beetle species and used time-course differential expression analysis to investigate gene expression differences in closely related species Galerucella pusilla and G. calmariensis that are, respectively, resistant and susceptible against parasitoid infection by Asecodes paividava parasitoids. Approximately 271 million and 224 million paired-ended reads were assembled and filtered to form 52,563 and 59,781 transcripts for G. pusilla and G. calmariensis, respectively. In the whole-transcriptome level, an enrichment of functional categories related to energy production, biosynthetic process, and metabolic process was exhibited in both species. The main difference between species appears to be immune response and wound healing process mounted by G. pusilla larvae. Using reciprocal BLAST against the Drosophila melanogaster proteome, 120 and 121 immune-related genes were identified in G. pusilla and G. calmariensis, respectively. More immune genes were differentially expressed in G. pusilla than in G. calmariensis, in particular genes involved in signaling, hematopoiesis, and melanization. In contrast, only one gene was differentially expressed in G. calmariensis. Our study characterizes important genes and pathways involved in different immune functions after parasitoid infection and supports the role of signaling and hematopoiesis genes as key players in host immunity in Galerucella against parasitoid wasps.

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  • Pollinators, Herbivores, and Plant Neighborhood Effects

    2020. Nora Underwood, Peter A. Hambäck, Brian D. Inouye. The Quarterly review of biology 95 (1), 37-57


    Pollinator and herbivore interactions with individual plants can be strongly influenced by the densities and frequencies of other plants in local neighborhoods. The importance of these neighborhood effects is not yet clear, due in part to a profound disconnect between studies of pollinator and herbivore neighborhood effects. Considering these effects jointly is critical for understanding the role of plant spatial heterogeneity because plant fitness is often affected by pollinators, herbivores, and their interactions. We bring together these two types of neighborhood effects, describing the pathways through which these insects mediate neighborhood effects, and comparing their implementation in mathematical models. We find that ideas from each field can improve work in the other. For example, pollinator theory should broaden consideration of how pollinator traits influence responses to plant neighborhoods, while herbivore theory should consider adaptive foraging and connect herbivore neighborhood effects to plant fitness. We discuss approaches to theory that integrate pollinator and herbivore effects, particularly considering the nested spatial and temporal scales of these insects' responses to neighborhoods. Ultimately, models will need to combine neighborhood effects from the diverse species that affect plants with direct plant interactions to determine the importance of spatial structure for plant performance and evolution.

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  • Seasonally varying marine influences on the coastal ecosystem detected through molecular gut analysis

    2019. Vasiliki Verschut (et al.). Molecular Ecology 28 (2), 307-317


    Terrestrial predators on marine shores benefit from the inflow of organisms and matter from the marine ecosystem, often causing very high predator densities and indirectly affecting the abundance of other prey species on shores. This indirect effect may be particularly strong if predators shift diets between seasons. We therefore quantified the seasonal variation in diet of two wolf spider species that dominate the shoreline predator community, using molecular gut content analyses with general primers to detect the full prey range. Across the season, spider diets changed, with predominantly terrestrial prey from May until July and predominantly marine prey (mainly chironomids) from August until October. This pattern coincided with a change in the spider age and size structure, and prey abundance data and resource selection analyses suggest that the higher consumption of chironomids during autumn is due to an ontogenetic diet shift rather than to variation in prey abundance. The analyses suggested that small dipterans with a weak flight capacity, such as Chironomidae, Sphaeroceridae, Scatopsidae and Ephydridae, were overrepresented in the gut of small juvenile spiders during autumn, whereas larger, more robust prey, such as Lepidoptera, Anthomyidae and Dolichopodidae, were overrepresented in the diet of adult spiders during spring. The effect of the inflow may be that the survival and growth of juvenile spiders is higher in areas with high chironomid abundances, leading to higher densities of adult spiders and higher predation rates on the terrestrial prey next spring.

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