Browsing by Author "Wetherington, Miles T."

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    Climate variation alters the synchrony of host-parasitoid interactions
    (2017) Wetherington, Miles T.; Jennings, David E.; Shrewsbury, Paula M.; Duan, Jian J.
    Observed changes in mean temperature and increased frequency of extreme climate events have already impacted the distributions and phenologies of various organisms, including insects. Although some research has examined how parasitoids will respond to colder temperatures or experimental warming, we know relatively little about how increased variation in temperature and humidity could affect interactions between parasitoids and their hosts. Using a study system consisting of emerald ash borer (EAB), Agrilus planipennis, and its egg parasitoid Oobius agrili, we conducted environmentally controlled laboratory experiments to investigate how increased seasonal climate variation affected the synchrony of host-parasitoid interactions. We hypothesized that increased climate variation would lead to decreases in host and parasitoid survival, host fecundity, and percent parasitism (independent of host density), while also influencing percent diapause in parasitoids. EAB was reared in environmental chambers under four climate variation treatments (standard deviations in temperature of 1.24, 3.00, 3.60, and 4.79 degrees C), while O.agrili experiments were conducted in the same environmental chambers using a 4x3 design (four climate variation treatmentsx3 EAB egg densities). We found that EAB fecundity was negatively associated with temperature variation and that temperature variation altered the temporal egg laying distribution of EAB. Additionally, even moderate increases in temperature variation affected parasitoid emergence times, while decreasing percent parasitism and survival. Furthermore, percent diapause in parasitoids was positively associated with humidity variation. Our findings indicate that relatively small changes in the frequency and severity of extreme climate events have the potential to phenologically isolate emerging parasitoids from host eggs, which in the absence of alternative hosts could lead to localized extinctions. More broadly, these results indicate how climate change could affect various life history parameters in insects, and have implications for consumer-resource stability and biological control.
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    Ecological succession and the competition-colonization trade-off in microbial communities
    (2022) Wetherington, Miles T.; Nagy, Krisztina; Dér, László; Ábrahám, Ágnes; Noorlag, Janneke; Galajda, Peter; Keymer, Juan E.
    Background: During range expansion in spatially distributed habitats, organisms differ from one another in terms of their patterns of localization versus propagation. To exploit locations or explore the landscape? This is the competition-colonization trade-off, a dichotomy at the core of ecological succession. In bacterial communities, this trade-off is a fundamental mechanism towards understanding spatio-temporal fluxes in microbiome composition. Results: Using microfluidics devices as structured bacterial habitats, we show that, in a synthetic two-species community of motile strains, Escherichia coli is a fugitive species, whereas Pseudomonas aeruginosa is a slower colonizer but superior competitor. We provide evidence highlighting the role of succession and the relevance of this trade-off in the community assembly of bacteria in spatially distributed patchy landscapes. Furthermore, aggregation-dependent priority effects enhance coexistence which is not possible in well-mixed environments. Conclusions: Our findings underscore the interplay between micron-scale landscape structure and dispersal in shaping biodiversity patterns in microbial ecosystems. Understanding this interplay is key to unleash the technological revolution of microbiome applications.
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    Expansion, Exploitation and Extinction : Niche Construction in Ephemeral Landscapes
    (2020) Wetherington, Miles T.; Keymer, Juan MI.
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    The spatial ecology of microbes
    (2021) Wetherington, Miles T.; Keymer, Juan E.; Pontificia Universidad Católica de Chile. Facultad de Ciencias Biológicas
    Guided by cell biophysics experimentation and equipped with toolsets from theoretical ecology, the aim of my thesis is to explore the ways in which spatial structure influences the dynamics and distributions of microbial cells, populations and communities. In my first project, we highlighted range expansion experiments of a colicin producing-colicin sensitive E.coli community on solid agar; The process of colony formation is driven by colicin production, cell lysis and division all driving the dynamical structure and ecological composition of the colony. Making analogies to percolation theory from statistical physics, we were able to develop a spatial model to quantify regimes of strain coexistence, competitive exclusion and extinction. Next we aimed to understand the spatial conditions under which microbial common goods games could persist. A particular bacterial system motivating this study was Pseudomonas aeruginosa, which excretes a costly ‘iron-scavenging’ compound (siderophore) in order to bind and transport iron across the cell membrane. This compound represents a common-pool resource, susceptible to exploitation by nearby bacteria free from producing this metabolically costly resource. With this system in mind we asked the following question: what spatial conditions permit these common-pool resources to be monopolized by a cooperator strategy in competition with an exploiter strategy? By developing a stochastic spatial model, we quantified the phase transition from monopolized to exploited and predicted which circumstances to expect coexistence between niche constructing and exploiter strategies as a result of differences in niche monopolization and colonization rates, respectively, and when to expect a collapse of the niche and a ‘tragedy of the commons’. Following this work, I began to apply newly acquired expertise in microfluidics, microfabrication techniques, microscopy and experimental cell biophysics in order to observe and study the spatial colonization dynamics of E.coli and P.aeruginosa in structured microfabricated landscapes. We showed how these two bacterial species enact a competition-colonization tradeoff where the faster colonizing E.coli can be overwhelmed locally by the slower but superior competitor, P.aeruginosa. This work constituted the first evidence of an abstract ecological theory in a spatial bacterial community. Furthermore, these results showed the importance of spatial structure in leading to coexistence as E.coli is able to effectively localize P.aeruginosa populations when competing in a patchy landscape via priority-effects. Conversely, in well-mixed ‘mean-field’ conditions the superior competitor always wins. In order to address the priority effects observed by E.coli, we made analogies to the Kronig-Penny model of solid state physics to our patchy landscape. To help understand the role habitat structure plays in the process of ecological colonization via invading wave populations, we represented our patchy landscapes as a periodic potential. An interesting result of such interpretation is the opening for the possibility of Anderson localization phenomena to take place; whereby species modulate each other’s dynamic habitat landscape. In this scenario E. coli cells modulate the potential seen by P.aeruginosa and introduce randomness to ecological corridors. In this way E. coli can induce strong localization in the spatial distribution of the P.aeruginosa metapopulation. This work highlights the importance of invisible corridor interactions and their potential to determine patterns of patch occupancy. Building on these results we next made an explicit connection between the topological properties of spatially structured microbial landscapes and Taylor’s Law, which asserts that the fluctuations within a metapopulation is a power law function of the mean. This statistical phenomena of populations, while well-documented in both the macro- and microscopic world, has yet to be connected to processes shaping spatially structured microbial populations and communities. Pursuing this analogy from solid state physics further we generated different degrees of randomness in the patchconnecting ecological corridor widths within a microfabricated microfluidics landscape, we found that a critical level of randomness leads to a qualitative transition in the fluctuation scaling of an Escherichia coli metapopulation. That induced randomness leads to such a result is neither expected experimentally nor completely understood theoretically. Nevertheless, these results bring a landscape perspective to Taylor’s law and the desire to connect this phenomena to ecological processes. Furthermore, bridging Taylor’s Law with other ecological scaling laws is an ongoing effort in the field of macroecology and one which we think would benefit from collaborations between theoreticians and experimental cell biophysics techniques like the one implemented here. Finally, given the unique perspective of this collaborative effort between cell biophysics and theoretical ecology, we conclude this thesis with a review of the literature in the field. Primarily, we focus on the necessary theoretical ecology needed for cell biophysicists to interpret their experimental results. In particular, we review landmark experimental cell biophysics discoveries from the past 15 years ranging from single-cell, population and community/biofilm studies, as well as following-up with newer findings all of which we discuss from an ecological viewpoint.
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    Variance in Landscape Connectivity Shifts Microbial Population Scaling
    (2022) Wetherington, Miles T.; Nagy, Krisztina; Der, Laszlo; Noorlag, Janneke; Galajda, Peter; Keymer, Juan E.
    Understanding mechanisms shaping distributions and interactions of soil microbes is essential for determining their impact on large scale ecosystem services, such as carbon sequestration, climate regulation, waste decomposition, and nutrient cycling. As the functional unit of soil ecosystems, we focus our attention on the spatial structure of soil macroaggregates. Emulating this complex physico-chemical environment as a patchy habitat landscape we investigate on-chip the effect of changing the connectivity features of this landscape as Escherichia coli forms a metapopulation. We analyze the distributions of E. coli occupancy using Taylor's law, an empirical law in ecology which asserts that the fluctuations in populations is a power law function of the mean. We provide experimental evidence that bacterial metapopulations in patchy habitat landscapes on microchips follow this law. Furthermore, we find that increased variance of patch-corridor connectivity leads to a qualitative transition in the fluctuation scaling. We discuss these results in the context of the spatial ecology of microbes in soil.