Spatio-temporal dispersal dynamics of a natural house sparrow metapopulation
Doctoral thesis
View/ Open
Date
2023Metadata
Show full item recordCollections
- Institutt for biologi [2667]
Abstract
Dispersal plays a critical role in determining eco-evolutionary dynamics by affecting population sizes and causing gene flow, which influence spatial correlations in demography and genetic structure of local populations. In fragmented landscapes, dispersal sets a bridge between subpopulations and may alter the fitness of individuals or subpopulations through generations, which may be crucial for viability of populations and persistence of species. Therefore, understanding the role of dispersal at the population and metapopulation levels is vital for predicting ecological and evolutionary processes, particularly in the face of habitat fragmentation and climate change currently observed for many populations. Nevertheless, studying dispersal in natural populations poses a formidable challenge as it requires accurate data to distinguish dispersers from residents.
To fulfill the need for improved methodology resulting in more accurate identification of dispersers and residents, I demonstrated an integrative method that utilizes genetic assignment, ecological capture-mark-recapture (CMR), and an extensive SNP-pedigree to determine individual origins and distinguish between immigrants and residents within a house sparrow metapopulation (paper I). After investigating the possible sources of genetic assignment errors, a dispersal dataset with high accuracy was constructed to use in subsequent studies, including the additional chapters in this thesis. For instance, this information allowed for the characterization of heritable genetic variation in dispersal phenotype. Since dispersal is expected to increase the level of genetic variation and hence possibly the adaptive potential of recipient populations, it is important to understand the causes of individual variation in the dispersal phenotype. By using a genetic groups animal model that allowed us to exploit all kinds of relationships between individuals as determined by a multi-generational pedigree of the house sparrow metapopulation, I showed that some of the observed variation in dispersal has a heritable genetic component (paper II). Additionally, a habitat-related variation in the relative importance of genetic and environmental effects for individual dispersal was detected, hinting that genotype by environment interactions (GxE) should be investigated further. Finally, a genome wide association study (GWAS) identified that a genomic region was related to dispersal probability. However, the top marker in this region explained only a small proportion of the variance in dispersal probability, suggesting that dispersal is a polygenic trait in the house sparrow metapopulation.
Since dispersal is expected to affect genetic structure of inter-connected populations, I wanted to provide a piece of empirical evidence on how immigration rate (m) and effective population size (i.e., Ne) affect population genetic structure as quantified by populationspecific genetic differentiation (population-specific FST) in natural populations (paper III). In fact, I showed that m and Ne can shape the spatial genetic structure by revealing a negative non-linear relationship between between Ne*m and population-specific FST meaning that there was a faster decline in population-specific FST for larger values of m as Ne increased and vice versa. To improve our understanding of ecological and evolutionary consequences of immigration on both population and metapopulation levels, it was equally important to explore fitness consequences of dispersal. Therefore, fitness consequences of dispersal for parent and offspring generations were investigated for annual survival, annual reproductive success (ARS), and lifetime reproductive success (LRS) in paper IV. I found that not only do the immigrants produce more offspring annually and throughout their lifetime than residents, but so do their offspring in comparison with offspring produced by two resident individuals. Additionally, I also showed that immigrant parents have a higher contribution to the metapopulation since they produced more offspring that emigrated to other populations than resident parents.
This thesis contributes to our understanding of the general patterns, genetic basis, and genetic and demographic consequences of dispersal in fragmented natural populations. More specifically, the results that I present here, highlight two main points: Firstly, I showed that genetic data can be used to obtain robust assessments of dispersal. Secondly, with this data, I was able to provide substantial empirical knowledge on the causes and consequences of dispersal, which shed light on basic theories, but that more empirical examples are required for validation of generality. Overall, the findings of this thesis suggest that dispersal is a crucial life-history trait that heavily impacts the genetic structure and has the potential to show adaptive evolution in populations of vertebrates in the wild.