Locating adaptive diversity in the face of climate change

Macdonald, Stewart (2016) Locating adaptive diversity in the face of climate change. PhD thesis, James Cook University.

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Abstract

Climate change will have profound and negative effects on the planet's biodiversity. Conservationists and land managers are turning to a variety of strategies with the hope of mitigating some of these effects. One such strategy is assisted gene flow (AGF): the translocation of individuals between populations with the aim of increasing genetic diversity and introducing specific 'preadapted' genes that will boost the climate change resilience of the recipient population. Assisted gene flow is already in use, and is likely to see increasing use in the coming decades, but the methods needed to deploy it effectively are still being developed. To mitigate climate change impacts, assisted gene flow will be most effective when the source populations are: 1) adapted to their local climate, and 2) close to the recipient population in future climate space.

This thesis details techniques that can be used to identify the environmental drivers of local adaptation (focusing specifically on climatic drivers), and weight them according to the degree to which they drive local adaptation. These weighted climatic axes can then be used to create a climate space that accounts for the degree to which each climatic axis is driving local adaptation; a space in which AGF source and recipient populations can be sensibly matched. These concepts and techniques are demonstrated in the following chapters using a case study of the Rainforest Sunskink (Lampropholis coggeri) from the rainforests of north-eastern Australia.

Chapter 1 reviews the threats caused by climate change and outlines some potential mitigation strategies, with particular emphasis on assisted gene flow and novel strategies to make AGF more effective. It then outlines the structure of the thesis and sets the scene for the development of these novel strategies.

Chapter 2 outlines the ecological factors that should be considered when searching for potential source populations: population size, connectivity, and climate. Knowing that isolation (i.e., low connectivity) is conducive to local adaptation, a connectivity index is developed that is used in the analyses that appear in subsequent chapters.

Given that we are looking for local adaptation to extreme climates, and knowing that isolation is conducive to local adaptation, Chapter 3 then explores the relationship between climatic extremity and habitat connectivity, and finds that more isolated rainforest habitat does indeed experience more extreme climate, and that these shifts towards extremity are in the direction of climate change. As such, isolated habitats, free from gene swamping and subject to extreme climates, are likely to contain populations adapted to the sorts of climates we expect to be more widespread in the future. It is these populations that will make ideal source populations for assisted gene flow strategies.

Chapter 4 develops a method for determining which aspects of the environment most strongly drive local adaptation. It does this by recognizing that high connectivity leads to high levels of gene flow, which erodes local adaptation. This method is demonstrated by determining which aspects of climate are the strongest drivers of local adaptation in the case study system. The relationships between various climatic variables and physiological and morphological traits in the focal skink species are examined, and the degree to which gene flow erodes these relationships is assessed using the connectivity index developed in Chapter 2. In my study system, this highlighted two precipitation variables (annual mean precipitation and precipitation of the driest quarter) as those aspects of climate that appear to be the strongest drivers of local adaptation.

Chapter 5 combines the connectivity index from Chapter 2 and the climatic drivers of local adaptation from Chapter 4, and develops a technique to match potential source and recipient populations, weighting climatic axes to account for the degree to which they drive local adaptation. It uses a case study involving L. coggeri to demonstrate this technique, and then discusses the results of the case study and the generality of the technique.

Finally, Chapter 6 summarises the main findings and suggests some avenues for future research.

This thesis brings together considerations from both ecology and evolution to argue that isolated patches of habitat on the edge of a species' range are likely to contain populations that will be of great importance if we are to conserve species in the face of climate change. The same characteristics that make these isolated populations so valuable (small size and extreme climates), however, also put them at the highest risk of extinction from climate change. Given the rapid rate at which climate change is progressing, the identification and conservation of adaptive diversity present in isolates is of utmost importance.

Item ID: 46232
Item Type: Thesis (PhD)
Keywords: adaptations; adaption to climate change; adaptive diversity; assisted gene flow; climate change; evolution; extreme climates; genetic adaptations; genetic diversity; genetics; Lampropholis coggeri; Lampropholis; Paluma Range; rainforests; skinks; sunskinks; Wet Tropics World Heritage Area
Date Deposited: 01 Nov 2016 23:36
FoR Codes: 06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060306 Evolutionary Impacts of Climate Change @ 100%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 100%
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