Local adaptation by birds to human-altered habitats: the great tit and the house sparrow as model species

Abstract

Human-altered environments have expanded rapidly in the past decades and made a huge impact on living organisms. Inhabiting in such a habitat can modify different traits in animals, allowing for a better adaptation to these human-altered environments. In the first part of this thesis I investigated patterns of recent (contemporary) adaptation to urban habitats, focusing on the role of behavioural, genetic and epigenetic variation in great tits. In the second part of the thesis I investigated patterns of adaptation to human-made habitats in a larger time-scale, focusing on the origin and expansion of the house sparrow, which has been for ages a human commensalism. I additionally checked the effect of methylation variation on the rapid expansion and high phenotypic variation of house sparrow in the Palearctic region. Regarding the great tit I found that urban-dwelling birds are more explorative in novel environments and bolder in front of new objects than forest individuals. I found several epigenetic modifications and genetic polymorphisms possibly related to novelty seeking behaviour in the great tits. Our results suggested that epigenetics adjustment can be different in the urban-dwelling great tits in comparison to the forest birds. Furthermore, we investigated the possible polymorphisms in the Melanocortin-1 gene in the great tit to relate it with the size of the black belly stripe, which had previously been found to differ between urban and forest individuals. However, results showed that there is no polymorphism in this gene in relation to the size of the black belly stripe. In relation to the house sparrow, we found that the commensalism of this species with humans has a single origin and probably initiated in the Middle East. Then, it expanded rapidly in the Palearctic region with the aid of agriculture and human civilizations expansion. In addition, we discovered that the genome-wide methylation pattern of house sparrows has a general stability within five subspecies in the Middle East but we found high level of variation at the individual level within populations which likely happened randomly rather than due to selection. Our results indicate that variation in DNA methylation does not strictly follow subspecies designations. We have detected correlation between methylation level and some morphological traits such as standardized bill length and we suggest that part of the high morphological variation in the native populations of the house sparrow is influenced by differentially methylated regions in specific loci throughout the genome. We also detected seven differentially methylated loci diverged by subspecies and also three loci differentiated by commensal or non-commensal status.