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

The main database is completed and contains 60,000 cases of cuckoo parasitism from whole of Europe. Analyses have been carried out in 2013-2015. Furthermore, the team has completed analyses of molecular data. The research team is now at the final stages writing 9 manuscripts that will be submitted to international peer-reviewed journals in 2015 and 2016. Overview of manuscripts in preparation (working titles): 1. Host specificity among individual cuckoo females 2. Host suitability - which characteristics are important for host selection by the cuckoo 3. Host density predicts cuckoo parasitism in suitable hosts 4. Spatial variation in host use by the cuckoo in Europe 5. Changes in breeding phenology of cuckoos and their hosts in Central Europe over 150 years 6. A single (ancient) matrilineal genetic origin of blue eggs in the common cuckoo 7. Genetic differentiation among cuckoo tribes in Europe 8. Non-destructive methods obtaining DNA from bird eggs stored at museums 9. Migration of juvenile cuckoos as disclosed by use of satellite transmitters In addition, we expect several other manuscripts to be published as spin-offs from the project. The project has continued to receive interest from mass media, resulting in several interviews and press releases.

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 b ring 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 e volve and be maintained in the face of homogenising 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 parasit e, 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 analyse 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 m aintained. 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