Browsing by Subject "population structure"
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(2021)Rapid environmental changes over the last 100 years have led to substantial range shifts across taxonomic groups. Understanding what facilitates successful shifts is important for predicting ecological consequences and planning efficient conservation actions. Interestingly, the very process of range expansion can affect the success of the shift by causing genetic changes in the expanding populations. Theory predicts that without sufficient gene flow, repeated founder events and strong genetic drift can result in allele frequency gradients and loss of genetic diversity along the expansion axis. Empirical studies testing these expectations in environment-driven range shifts are still relatively scarce, and how range expansions affect genetics in highly mobile species remains unclear. In this study, I investigated the genetic consequences of a recent range expansion in a long-distance migratory passerine, the reed warbler (Acrocephalus scirpaceus). Utilizing genome-wide data from restriction site-associated DNA sequencing (RAD-seq), I studied whether the expansion was reflected in either population structure or genetic diversity of the recently established Finnish range edge population. Despite philopatry and genetic differentiation to the range core populations, principal component analysis (PCA) and a model-based Bayesian clustering approach (fineRADstructure) revealed a lack of spatial population structure along a putative colonization route. Levels of genetic diversity, based on expected heterozygosity, nucleotide diversity, and private allele count, were found to be very similar between range edge (Finland) and range core (Central Europe). The results likely indicate high levels of gene flow both within the new population and across greater spatial distances during or after the range expansion. Due to a detected sequencing batch effect, however, the exact diversity estimates must be considered preliminary. These findings suggest that species with high enough dispersal propensity may escape the predicted genetic costs of range expansions, retaining high levels of genetic variation at range margins. This study provides valuable insights for understanding range shifts in mobile taxa, and highlights the need to investigate further the traits of species that enable the preservation of evolutionary potential during range shifts.
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(2021)The European rabbit (Oryctolagus cuniculus) is a small mammal native to the Iberian Peninsula, but introduced by humans to all continents except Antarctica. The rabbit has been a remarkably successful invasive species due to its generalist nature and fast reproduction. Its spreading has mostly been destructive to the local nature, and humans have used fatal rabbit diseases such as rabbit haemorrhagic disease (RHD) to control harmful populations. The rabbit population in Helsinki is one of the most northern annually surviving rabbit populations in the world. It is believed to have originated from escaped pet rabbits in the late 1980s, and in the early 2000s, the rabbits spread rapidly around the Helsinki area. RHD spread unintentionally to Finland in 2016, and the disease caused a significant reduction in the Helsinki rabbit population. Rabbit population genetics has previously been studied in several countries, but never before in Finland. The aim of the thesis was to examine the genetic diversity and population structure of the Helsinki rabbit population before and after the RHD epidemic, and to compare the results to similar preceding rabbit population genetic studies. Rabbit populations have previously been found to recover from major population crashes without a notable loss in genetic diversity using DNA microsatellite markers. The recent RHD epidemic in Helsinki provided an opportunity to study, whether a rabbit population can recover from a population crash even in a harsher environment without losing genetic diversity. To conduct genetic analysis, fourteen DNA microsatellite loci were genotyped from individuals caught during two distinct time periods, in 2008-2009 (n=130) and in 2019-2020 (n=59). Population structure was observed in both temporal rabbit populations with small but significant FST values. The 2019-2020 population was more diverse than the 2008-2009 population in terms of allele numbers and expected heterozygosity. This result was unexpected considering the recent RHD-epidemic but could be explained by gene flow from new escaped rabbits. Compared to other wild rabbit populations around the world, the Helsinki area rabbits exhibit significantly lower genetic diversity. Bottleneck tests showed a significant signal separately in both temporal populations, but the RHD bottleneck cannot be distinguished based on the tests. The results could be biased by new gene flow, or the initial bottleneck caused by the founder effect of only a few pet rabbits. The rabbits have demonstrated their adaptation and survival skills in the cold climate of Helsinki. The population has significantly lower genetic diversity compared to other wild populations, yet recovered from a major RHD epidemic without reduction in genetic diversity under these more extreme environmental conditions. It has been proven again; the rabbit is a thriving invasive species.
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