Browsing by Author "Wagener, Carla"

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    The cost and complexity of assessing impact
    (Pensoft, 2020-10-15) Measey, John; Wagener, Carla; Mohanty, Nitya Prakash; Baxter-Gilbert, James; Pienaar, Elizabeth F.
    ENGLISH ABSTRACT: The environmental and socio-economic impacts of invasive species have long been recognised to be unequal, with some species being benign while others are disastrous. Until recently there was no recognised standard impact scoring framework with which to compare impacts of species from very different taxa. The advent of the Environmental Impact Classification for Alien Taxa (EICAT) and Socio‐Economic Impact Classification of Alien Taxa (SEICAT) schemes allows for the possibility of assessing impact through a standard approach. However, both these schemes are still in their infancy and the associated costs of the research that informs them is unknown. We aimed to determine the study costs and complexity associated with assessing invasive species’ socio-economic and environmental impacts. We used amphibians as a model group to investigate papers from which EICAT and SEICAT scores could be drawn up to 2019. Our analysis shows that studies that resulted in higher impact scores were more costly. Furthermore, the costs of studies were best predicted by their complexity and the time taken to complete them. If impact scores from EICAT and SEICAT are allowed to inform policy, then we need to carefully consider whether species with low scores represent true impact, or require more research investment and time. Policy makers needing accurate assessments will need to finance larger, more complex, and rigorous studies. Assessing impacts in low and middle income countries may need investment using international research collaborations and capacity building with scientists from high income areas.
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    Spill your guts: the invasive amphibian gut microbiome
    (Stellenbosch : Stellenbosch University, 2021-03) Wagener, Carla; Measey, John; Du Plessis, Morne; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: Invasive vertebrate species threaten global biodiversity, and significantly impact economic, agricultural and ecosystem services. Alarmingly, the number of introductions of species into non-native areas are increasing. Invasive species are introduced along with non-native microorganisms living in or on their hosts. In plant and insect invasions it has been shown that symbiotic relationships with microbial communities (collectively known as the microbiome) can enhance invasive species performance and facilitate establishment of non-native species in new environments. However, no studies have determined which factors impact the invasive vertebrate microbiome and how different microbial communities might facilitate vertebrate invasions. Therefore, in the aim of this thesis was to study how introduction of a vertebrate species into novel environments alters it’s gut microbial communities and it’s predicted functional capabilities, as well as whether the gut microbiome and it’s functional profiles can respond adaptively to environmental change and how these responses (or lack thereof) affect host physiology and, ultimately, fitness. To address the first aim outlined above, I made use of next-generation DNA sequencing (NGS) techniques to characterise the gut bacterial communities of guttural toad (Sclerophrys gutturalis) invasive populations in Mauritius, Réunion and Cape Town with varying residence times and compared these to their native source population in Durban. This allowed me to test whether residence time impacts the gut microbial compositional, phylogenetic and functional divergence across guttural toad populations. Additionally, I characterised the gut microbiome of an expanding invasive population (Cape Town) to determine how residence time impacts gut microbial divergence across the core and periphery. To address my second aim, I conducted reciprocal faecal microbial transplant experiments on native and invasive guttural toads in Durban (native area) and Cape Town (invasive area). Thereafter I exposed toads to one of two diets: natural or a dietary challenge and subsequently collected faecal microbial material in order to determine compositional, phylogenetic and functional microbial responses of toads to a novel dietary challenge. Additionally, I measured physiological performance and organ mass of toads. I found that gut microbial communities are compositionally distinct across all invasive populations. However, only the youngest population had a phylogenetic and functionally distinct microbiome. Therefore, I found that residence time does not impact the gut microbiomes of invasive guttural toads and instead I suggest that invasion pathways (i.e. the life history of toads at introduction) might be a more important factor determining gut microbiome divergence. I found that the invasive Cape Town microbiome has adaptively diverged to become compositionally, phylogenetically and functionally flexible in response to a novel dietary challenge compared to the native Durban microbiome. Functional pathways known to increase digestive efficiency, additionally increased in abundance in the invasive microbiome. I also found that this microbial flexibility facilitates flexibility in energy investments in hosts. Although physiological performance did not vary across diets, performance was significantly higher in toads with invasive gut microbiomes. Thus, I show for the first time that the gut microbiome facilitates ecological adaptation in an invasive amphibian population.