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Ecological immunology

The ecology and evolution of host-parasite interactions
Infectious diseases are a common problem for most organisms. Genes involved in resistance to parasites and pathogens can therefore be expected to be under strong natural selection.

Natural selection on immune genes

In this project we investigate the evolutionary consequences of pathogen-mediated selection at the molecular genetic level. We are currently focusing on how natural selection acts on various receptors involved in innate immunity, such as toll-like receptors. We are interested in questions like: Do genes encoding receptors of innate immunity evolve relatively fast or slow? What is the genetic diversity of innate receptors? How does it vary in time and space? What factors maintain diversity? Our main study system is wild rodents and a variety of pathogens, in particular the tick-transmitted bacterium Borrelia afzelii and the intestinal parasite Heligmosomoides.

A picture of a bankvole in snow

Selected publications:

Tschirren B, Andersson M, Scherman K, Westerdahl H and Råberg L. 2013. Polymorphisms at the innate immune receptor TLR2 are associated with Borrelia infection in a wild rodent population. Proceedings of the Royal Society, London B 280:20130364.

Tschirren B, Andersson M, Scherman K, Westerdahl H and Råberg L. 2012. Contrasting patterns of diversity and population differentiation at the innate immunity gene toll-like receptor 2 (TLR2) in two sympatric rodent species. Evolution 66: 720-731.

Tschirren B, Råberg L and Westerdahl H. 2011. Signatures of selection acting on the innate immunity gene TLR2 during the evolutionary history of rodents. Journal of evolutionary biology 24:1232-1240.

Resistance vs tolerance to pathogens

Defences against pathogenic microbes and other parasites can be divided into two conceptually different components: resistance (the ability to control parasite loads) and tolerance (the ability to minimize the fitness consequences of a given parasite load). It is important to distinguish between these two types of defence because they have radically different consequences for the epidemiology of infectious diseases, and the coevolution between hosts and parasites. The genes and mechanisms mediating resistance are well known, but our understanding of tolerance is still rudimentary. We study the genetics of tolerance, in particular whether tolerance and resistance are genetically correlated or independent traits. Our main study system is laboratory mice and various intestinal pathogens.

Selected publications:

Råberg L and Stjernman M. 2012. The evolutionary ecology of infectious disease virulence. In: Ecoimmunology (eds: G Demas and R Nelson). Oxford University Press.

Råberg L, Graham A, Read AF. 2009. Decomposing health: resistance and tolerance to parasites in animals. Philosophical Transactions of the Royal Society B 264:37-49.

Råberg L, Sim D and Read AF. 2007. Disentangling genetic variation for resistance and tolerance to infectious diseases in animals. Science 318:812-814.

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People involved



  • The Swedish Research Council (VR) 
  • The Crafoord Foundation