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Subject: search.filters.subject.310405 Evolutionary ecology

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    Social dynamics in natural populations of Dictyostelium discoideum : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Evolution at Massey University, Auckland, New Zealand
    (Massey University, 2024-12-05) Broersma-Stam, Cathleen
    Evolutionary theory predicts that selection should favour individuals who act in their self-interest, resulting in widespread selfish behaviour. Nonetheless, cooperative behaviours that provide benefits to others are common in nature. Over the past 50 years, evolutionary biologists have established a framework to explain how cooperation can be maintained despite the threat of selfish individuals who fail to cooperate but benefit from the cooperation of others. This framework has mostly been built around social behaviours in animal societies such as social insects. However, the more recent discoveries of social behaviours in microbes, analogous to those observed in animals, allow us to examine the generality and importance of proposed mechanisms that limit selfishness in non-animal societies. The social amoeba Dictyostelium discoideum has become an established model system in social evolution studies. Upon starvation, genetically unrelated cells can co-aggregate to form a ‘chimeric’ fruiting body in which some cells altruistically die to form a supportive stalk while others become viable spores. Theory and empirical work have shown that altruistic stalk formation can select for cheaters: genotypes that preferentially allocate cells to the spores and exploit stalk formation by their social partner. This finding has led to a considerable number of studies that demonstrated proof-of-principle for mechanisms that both promote and limit cheating in this organism. In contrast, few studies have examined whether cheating is widespread in nature, nor assessed the importance of the previously identified mechanisms that may limit this behaviour. In this thesis, I aimed to bridge the gap between the laboratory and a more natural situation. Using a diverse collection of natural strains of D. discoideum, I investigated the frequency and intensity of cheating among natural strains, the mechanisms that limit this behaviour, and the potential evolutionary consequences of interactions between cheaters and cooperators. Overall, this thesis will contribute to the growing body of work that examines how cooperative behaviours can be maintained in non-animal societies.
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    Intragenomic epistasis negatively impacts within-species coevolutionary arms races : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Biological Sciences at Massey University, Albany, New Zealand
    (Massey University, 2024) McFadyen, Sean Lewis
    Cooperation is susceptible to exploitation by selfish individuals. These individuals, referred to as cheaters, gain the benefits of cooperation without paying the costs. Cheating can select for individuals who can resist or prevent cheating, and resistance can in turn select for individuals that overcome the resistance. Thus, cheating and resistance potentially coevolve and lead to an arms race of adaptations and counter adaptations. Within a species, the existence of such an arms race is complicated by sexual reproduction among individuals that harbor alleles encoding the different strategies. Sexual reproduction will generate recombinants that harbor both cheating and resistance alleles. The impact of this recombination should depend on the extent of epistasis: that is, how the combined effects of these mutations differ from their effects individually. The goal of this thesis is to address how sexual reproduction impacts a within-species coevolutionary arms race, in this case, between cheating and resistance. The model organism Dictyostelium discoideum provides the perfect model to answer these questions. It has a unique life cycle, consisting of a unicellular (amoeba) stage, cooperative multicellular development (resulting in the formation of a fruiting body), and facultative sexual reproduction (resulting in the formation of a resting structure, termed a macrocyst). During the formation of the multicellular fruiting body, some cells are sacrificed to build a rigid stalk of dead cells that supports the rest. Cheaters exploit this altruistic sacrifice, and resistors prevent the cheaters from cheating. Resistance may in turn select for more efficient cheating, and this reciprocal selection can potentially spark a within-species arms race. During the sexual reproduction phase, recombination can then mix and match alleles encoding conflicting strategies into a single genetic background, allowing for epistatic effects to occur. Here I use the model organism Dictyostelium discoideum to understand how coevolution of cheating and resistance is impacted by sexual reproduction. To do so, I carried out a long-term evolution experiment to select for cheating and resistance. To understand the impact of recombination, I evolved replicate populations with or without periodic recombination. To address experimental difficulties, I also carried out an experiment to determine the optimal germination method for macrocysts produced during the Dictyostelium sexual cycle. Finally, I used computer simulations of the co-evolutionary process in Dictyostelium discoideum to explore how recombination and epistasis impact co-evolution, which allowed me to vary parameters of interest over a broader range of values than was possible in the laboratory. My findings suggest that recombination and resulting epistatic effects between conflicting strategies may prevent or slow within species co-evolutionary arms races.
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    New horizons for female birdsong : evolution, culture and analysis tools : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Auckland, New Zealand
    (Massey University, 2020) Webb, Wesley
    As a result of male-centric, northern-hemisphere-biased sexual selection theory, elaborate female traits in songbirds have been largely overlooked as unusual or non-functional by-products of male evolution. However, recent research has revealed that female song is present in most surveyed songbirds and was in fact the ancestral condition to the clade. Additionally, a high proportion of songbird species have colourful females, and both song and showy colours have demonstrated female-specific functions in a growing number of species. We have much to learn about the evolution and functions of elaborate female traits in general, and female song in particular. This thesis extends the horizons of female birdsong research in three ways: (1) by revealing the broad-scale evolutionary relationship of female song and plumage elaboration across the songbirds, (2) by developing new accessible tools for the measurement and analysis of song complexity, and (3) by showing—through a detailed field study on a large natural metapopulation—how vocal culture operates differentially in males and females. First, to understand the drivers of elaborate female traits, I tested the evolutionary relationship between female song presence and plumage colouration across the songbirds. I found strong support for a positive evolutionary correlation between traits, with female song more prevalent amongst species with elaborated female plumage. These results suggest that contrary to the idea of trade-off between showy traits, female plumage colouration and female song likely evolved together under similar selection pressures and that their respective functions are reinforcing. Second, I introduce new bioacoustics software, Koe, designed to meet the need for detailed classification and analysis of song complexity. The program enables visualisation, segmentation, rapid classification and analysis of song structure. I demonstrate Koe with a case study of New Zealand bellbird Anthornis melanura song, showcasing the capabilities for large-scale bioacoustics research and its application to female song. Third, I conducted one of the first detailed field-based analyses of female song culture, studying an archipelago metapopulation of New Zealand bellbirds. Comparing between male and female sectors of each population, I found equal syllable diversity, largely separate repertoires, and contrasting patterns of sharing between sites—revealing female dialects and pronounced sex differences in cultural evolution. By combining broad-scale evolutionary approaches, novel song analysis tools, and a detailed field study, this thesis demonstrates that female song can be as much an elaborate signal as male song. I describe how future work can build on these findings to expand understanding of elaborate female traits.