Browsing by Subject "Speciation"

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  • Kulmuni, Jonna; Nouhaud, Pierre; Pluckrose, Lucy; Satokangas, Ina; Dhaygude, Kishor; Butlin, Roger K. (2020)
    Speciation underlies the generation of novel biodiversity. Yet, there is much to learn about how natural selection shapes genomes during speciation. Selection is assumed to act against gene flow at barrier loci, promoting reproductive isolation. However, evidence for gene flow and selection is often indirect and we know very little about the temporal stability of barrier loci. Here we utilize haplodiploidy to identify candidate male barrier loci in hybrids between two wood ant species. As ant males are haploid, they are expected to reveal recessive barrier loci, which can be masked in diploid females if heterozygous. We then test for barrier stability in a sample collected 10 years later and use survival analysis to provide a direct measure of natural selection acting on candidate male barrier loci. We find multiple candidate male barrier loci scattered throughout the genome. Surprisingly, a proportion of them are not stable after 10 years, natural selection apparently switching from acting against to favouring introgression in the later sample. Instability of the barrier effect and natural selection for introgressed alleles could be due to environment-dependent selection, emphasizing the need to consider temporal variation in the strength of natural selection and the stability of the barrier effect at putative barrier loci in future speciation work.
  • Miraldo, Andreia; Wirta, Helena; Hanski, Ilkka (2011)
    Madagascar has a rich fauna of dung beetles (Scarabaeinae and Aphodiinae) with almost 300 species described to date. Like most other taxa in Madagascar, dung beetles exhibit an exceptionally high level of endemism (96% of the species). Here,we review the current knowledge of the origin and diversification of Malagasy dung beetles. Based on molecular phylogenies, the extant dung beetles originate from eight colonizations, of which four have given rise to extensive radiations. These radiations have occurred in wet forests, while the few extant species in the less successfu lradiations occur in open and semi-open habitats. We discuss the likely mechanisms of speciation and the ecological characteristics of the extant communities, emphasizing the role of adaptation along environmental gradients and allopatric speciation in generating the exceptionally high beta diversity in Malagasy dung beetles. Phylogeographic analyses of selected species reveal complex patterns with evidence for genetic introgression between old taxa. The introduction of cattle to Madagascar 1500 years ago created a new abundant resource, onto which a few species have shifted and thereby been able to greatly expand their geographical ranges.
  • Matara-aho, Minja (Helsingin yliopisto, 2020)
    Uranium and thorium are naturally occurring radionuclides with trace concentrations found in seawater. The growing use of nuclear energy has increased the risk of non-negligible releases of radioactivity into the environment. Most of the radioactivity is derived from uranium, which is why it is essential to understand more about the speciation of uranium in seawater and evaluate its possible impact on living organisms. The significance of thorium speciation studies rises from the use of plutonium, a more toxic actinide used in nuclear activities. Thorium is chemically similar to plutonium but less toxic and with simpler solution chemistry, so it can be used as an analogue for plutonium speciation studies. In this thesis, the role of earth alkaline cations in the structure of uranyl carbonate complex was investigated. The Ca2UO2(CO3)3 complex was previously identified as the main uranyl species in seawater but the role of calcium cations in the structure was not yet established. We prepared artificial seawater free of Mg2+ and Ca2+ using Sr2+ as a spectroscopic probe, spiked it with uranium ([U]=5·10-5 M) and measured with EXAFS spectroscopy. Together with FTIR spectroscopy and DFT calculations, the formation of Sr2UO2(CO3)3 complex was identified. Bioaccumulation of uranium was studied in sea urchins in a marine-like environment exposing the sea urchins to uranium for at least 200 hours. The U concentration in the seawater was followed throughout the experiment and at the end of the experiment the sea urchins were sacrificed and measured with ICP-OES. Accumulation of uranium was found mostly in the entrails of the sea urchins and in the excrement. The measured U from the seawater settled to about 10 % of the added uranium suggesting that there might be an equilibrium between seawater, sea urchins and sand. Th stability in seawater was studied by using Xylenol Orange as a colored complexing agent and UV-vis spectroscopy to follow the change in thorium concentration in time. Results show that thorium is rather stable in seawater if it is examined with Teflon covered instruments to prevent the thorium adsorption onto surfaces.