ERC - Stokke - Understanding the evolution and maintenance of host range in a generalist parasite - the paradox of sympatric host races, 2014

Generalist parasites may expand to new host species, or change the geographic range over which they exploit their hosts, as exemplified by emerging diseases and novel parasites in humans, domesticated plants and animals. Parasite range modifications may bring different host races into contact, facilitating gene flow among them. Sympatric host races of generalist parasites that maintain distinct adaptations to their different hosts represent a great puzzle in evolutionary biology. How can such host races evolve and be maintained in the face of homogenizing gene flow?

The aim of the proposed project is to understand the factors that influence evolution and maintenance of host range in a generalist parasite, the common cuckoo Cuculus canorus. In this parasite, individual females specialize on one or a few host species and have evolved specific egg morphs that mimic perfectly those of their hosts. I have compiled a unique database of nearly 40,000 parasitized host clutches found across Europe spanning ca. 200 years, and I will collect phenotypic and genetic data for ca. 2,500 cuckoo eggs stored in European museums. I will analyze spatial and temporal distributions of host races and parasite traits across Europe and determine levels of genetic differentiation and gene flow among host races at both neutral and functional loci. This will allow me to identify factors that determine host range, genetic differentiation and levels of adaptation, and shed light on how host-specific races of parasites evolve and are maintained. Understanding host specificity and host range in a widely distributed generalist parasite will not only have an impact on evolutionary theory, but also with possible ramifications for conservation and veterinary and medical health issues.