Novel allele advantage in guppies

How do the vertebrate immune genes of the Major Histocompatibility Complex (MHC) maintain such extraordinary levels of genetic polymorphisms? This question dates back from the 1970s, and one of the earliest hypotheses suggested a mechanism called “novel allele advantage”. Novel alleles of hosts from distant populations are thought to be better at recognising parasites because those parasites have not yet evolved mechanisms to avoid immune detection by those alleles. This classic hypothesis has been rarely tested. In collaboration with colleagues from Cardiff University and Poland, we examined this hypothesis using a well-known model system, the tropical freshwater fish guppies and their gyrodactylid parasites. We collected guppies from Trinidad and made crosses with guppies from Tobago. The first and second generation (F1 and F2) offspring were then infected with parasites from Tobago, and we tested whether the Trinidadian MHC alleles were better in defending against the Tobagonian parasites than the alleles from the Tobagonian guppies. As predicted by the classic theory, the “novel” immigrant alleles outperformed the resident alleles, thus confirming that immunological novelty can confer a selective advantage in the battle against parasites. The paper was published in PNAS (, and a “Behind the Paper” article describing the challenges we faced during this research was published in Nature Ecology & Evolution (Nature Ecology & Evolution – Behind the Paper).


Earlham institute
Quadram Institute Bioscience
John Innes Centre
The Sainsbury Laboratory
University of East Anglia

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