The spatial scale of immune gene variation within and among bottlenecked populations

The general aim of this thesis is to explore different spatial scales at which pathogen-mediated selection drives the evolution of immune genes across and within populations of Berthelot’s pipit (Anthus berthelotii), a historically bottlenecked passerine endemic to the oceanic islands of the Canary, Selvagens and Madeira archipelagos. I first investigated the evolution of key innate immune genes among the populations that the pipits inhabit. I found that while demographic history has played the major role in shaping patterns of among population variation at toll-like receptor loci, balancing selection (possibly pathogen-mediated) appears to have helped maintain functional variation at some specific loci. Second, I assessed the contribution of environmental factors to pathogen distribution and their subsequent effects on the major histocompatibility complex (MHC) class I genes of the acquired immune system within the population on Tenerife. I found a high prevalence of malaria in this population, the presence of which was correlated with climatic and anthropogenic variables: temperature, distance to poultry farms and distance to artificial water sources. Within the MHC I found evidence of trans-species polymorphism and gene conversion, and signatures of positive selection. Using landscape genetic analysis methods I found no evidence for overall within population patterns of structure at either neutral markers or the MHC. However, one MHC allele was associated to malaria infection risk and its distribution was (more strongly) associated with distance to poultry farms. These results suggest that demographic processes are the most important evolutionary force shaping variation at functional loci in isolated, bottlenecked populations. Nevertheless, selection can also shape patterns of variation at immunity loci, both at the coarser and the finer landscape scale, apparently in response to pathogens. This study therefore highlights the importance of considering different spatial scales when studying the evolutionary processes that shape functional genetic variation within populations.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Gonzalez Quevedo, Catalina

Language dc:language

en