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- W2949496670 abstract "Independent populations that evolve similar traits when inhabiting similar environments provide a powerful way to study adaptation. This process is known as convergent evolution and has been found across species, from the evolution of armour plating in sticklebacks in freshwater environments, to the evolution of wings in bats, birds and insects. Although adaptation is an old concept and it has been studied intensely over the recent past, we still remain largely ignorant about the genetics underlying this process, and therefore some of the most fundamental aspects of adaptation remain untested. In particular, we know very little about how natural selection drives trait evolution in independent populations, and whether such populations utilise the same genetic variation to evolve similar traits. We also lack an understanding of how trait evolution contributes to population divergence and whether it can directly lead to formation of new species. Here, I contribute to our understanding of the genetics of adaptation and divergence by studying an Australian wildflower, Senecio lautus, where two growth habits have evolved repeatedly and independently in adjacent and contrasting environments along the Australian coast. A prostrate growth habit is present in the rocky and windy headlands, whereas an erect growth habit is present in the adjacent sand dunes. A previous study found that sets of genes connected by similar functions and pathways were repeatedly differentiated in many of these adjacent Dune and Headland populations. One of these sets of genes was the auxin pathway. Auxin is a hormone that is transported from cell to cell to alter the direction of growth of the plant, from a stimulus such as light or gravity. I hypothesise that differences in the auxin pathway are responsible for the divergent growth habits between adjacent Dune and Headland populations. Arabidopsis mutants have shown that mutations in genes within the auxin pathway often result in a decreased ability to respond to an auxin controlled stimulus, such as gravity. Thus, to investigate divergence in the auxin pathway, I examined differences in the response to gravity (gravitropism). This was achieved through a gravitropism assay which assesses the ability of a seedling to alter its direction of growth after a 90° rotation. My results suggest that the auxin pathway was repeatedly utilised in the evolution of growth habit in many S. lautus populations adapting to their environment. I found that families with parents with a prostrate growth habit survived for longer when planted into the windy headland environment. This is coupled with a strong correlation between growth habit and gravitropism across S. lautus populations. For example, Dune populations are often erect and gravitropic (respond strongly to gravity stimuli) and Headland populations are often prostrate and agravitropic (respond poorly to gravity stimuli). To investigate whether gravitropism was driven by natural selection, I exposed an advanced recombinant population, derived from a cross between a pair of Dune and Headland populations, to three generations of natural selection in the dune and headland environment. I found evidence that natural selection was targeting gravitropic plants in the dune environment, whereby the fittest families in the dune environment produce offspring that are more gravitropic. Additionally, I found gravitropism variation is coupled with intrinsic reproductive isolation, suggesting gravitropism (or a tightly correlated trait) is not only important for adaptation but also for divergence between Dune and Headland populations. To further explore the genes involved in the evolution of gravitropism, an F11 recombinant population derived from Dune and Headland individuals was phenotyped and grouped into gravitropic and agravitropic individuals. These groups were sequenced and the genetic differences between them appear to lie in genes with functions related to the auxin pathway, the abscisic acid pathway, transport, localisation and salt tolerance. Some of the alleles with the greatest genetic differences between gravitropic and agravitropic individuals can predict fertilisation success. These results support my hypothesis that the auxin pathway is under selection and contributing to the divergence of adjacent Dune and Headland populations. Overall, my results indicate that independent populations adapting to similar environments can utilise the variation contained in a genetic pathway to evolve similar traits. I provide evidence that the auxin pathway is repeatedly utilised by S. lautus populations in the evolution of growth habit and gravitropism when adapting to dune and headland environments. Additionally, the evolution of gravitropism appears to contribute to population divergence by reductions in fertilisation success. Thus, my research has furthered our understanding of the genetics underlying the process of how natural selection drives adaptation and how this can directly lead to the formation of new species. Widening our knowledge on the genetic basis of adaptation and divergence in new systems will increase our ability to make generalisations across taxa for how evolution and speciation occur at the genetic level." @default.
- W2949496670 created "2019-06-27" @default.
- W2949496670 creator A5067935696 @default.
- W2949496670 date "2019-05-14" @default.
- W2949496670 modified "2023-09-27" @default.
- W2949496670 title "The genetic basis of adaptive evolution and divergence in an Australian wildflower" @default.
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