School of BioSciences - Theses
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ItemThe evolution of life-history, dispersal, and plasticity: expanding the Daphnia model( 2021)It is often noted that, in the face of accelerating environmental change, species must adapt or disperse in order to avoid extinction. Increasingly, however, it is recognised that we might need to refrain from seeing these concepts as independent. The integration of dispersal as a plastic, evolving trait within the framework of life-history is critical to our understanding of evolution in changing environments. Through dispersal an individual’s environment can change, but so too does the environment change an individual’s dispersal decisions. While the role of dispersal has gained appreciation, the drivers and genetic underpinnings of dynamic dispersal have only begun to be explored. Currently, there are few models which explore the spatial facet of life-history evolution. This thesis details the key first steps in the development of a spatially explicit model for life-history evolution using the Australian water flea, Daphnia carinata. This process began with the collection of Daphnia clones from sites across south-eastern Australia to establish a laboratory population for experimentation, phenotyped for life-history traits. The effect of natural selection on traits is heavily influenced by the genetic and environmental relationships of correlated traits and this is reflected in locally adapted life-history strategies. I therefore use a lens of habitat permanency to explore the life-history strategies of Daphnia from temporary and permanent habitats to test for evidence of local adaptation. Using classic life-table experimentation and analysis I find that D. carinata clearly demonstrate life-history strategies that covary with features of habitat permanence. I analyse the environmental robustness of these life-history strategies by using a multivariate reaction norm approach and phenotypic trajectory analysis of plastic responses to two different stressors: food restriction and predation threat. The plasticity employed by organisms to navigate the variation in their local habitat may play a critical role in further evolution of adaptive responses to novel or extreme environments. When plasticity is in the direction of selection this may have consequences for the rate and trajectory of evolution, but identifying if plasticity is adaptive is not straightforward. With a multi-environment, multivariate approach I assess whether plasticity in this population shows evidence of a stressor specific response, and whether the populations demonstrate genetic variation in multivariate plasticity. I find that this population does not demonstrate a general response to the two stressors and that nature of plasticity also varies between habitat groups. Finally, I establish methods for measuring passive and active dispersal in Daphnia. I calculate clonal repeatability as a measure of broad-sense heritability to determine the suitability of a suite of dispersal measures to the relationship of dispersal with other life-history traits. Daphnia display high levels of intraclonal variation in measures of active dispersal, indicative of the diverse environmental drivers of this complex trait. I find that the effect of the environment on aspects of dispersal, from decision to disperse to distance travelled, often leads to low repeatability estimates. However, this suggests that the tools I have developed in measuring adaptive plasticity will be useful in studying the spatial aspect of life-history in this system.