Browsing by Subject "Interactions"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Interactions between domestic, invasive and threatened carnivores and their implications in conservation and pathogen transmission
    (2013-07) SepĂșlveda, Maximiliano Alvaro
    When two individuals occur at the same place and time, a contact interaction occurs. In conservation, interactions between domestic animals and/or invasive species and wildlife pose a significant threat to endangered populations due to direct conflict, conflict over resources and, possibly most concerning, risk of infectious disease. However, in most cases, these interactions are not well characterized, particularly related to the drivers of why species interact, making managing these risks challenging. This is particularly true for disease risk. For infectious pathogens, such contact provides the most critical event for their persistence: disease transmission. In carnivores, this question of transmission and persistence is even more acute. In general, carnivores have low population densities and direct interactions with other carnivores tend to be rare or avoided. How, then, do diseases persist in these populations? This dissertation investigated the factors that drive interactions between species using a multi-species carnivore model composed of domestic dogs, invasive American mink and endangered Southern river otters in the Temperate Forest of Chile. Of particular interest as a model disease in this system was Canine Distemper Virus (CDV), a multi-host pathogen of carnivores and a disease of high conservation concern for endangered carnivores around the world. Previous work in wildlife indicates that multi-host systems are critical to the persistence of CDV in wild carnivores, making understanding interactions in a multi-carnivore system particularly important. Using this multi carnivore system, three studies were undertaken to better characterize drivers of carnivore interactions across species: Study 1 investigated how human management and use of domestic dogs influences dog-wildlife interactions using rural household surveys. Study 2 characterized domestic dog use of the landscape and risk factors for movement into protected areas and wildlife habitat. Finally, study 3 determined disease transmission risk among the three carnivore populations by characterizing interactions through household interviews and camera trapping using CDV as a model disease system. Results from Study 1 determined that dog-wild carnivore interactions are highly associated with dog's role as a guardian of livestock and are often encouraged by owners. This is in contrast to interactions with prey species that were associated with inadequate diet and were considered undesirable. Humans also shaped rural dog's demography dramatically, controlling their population through culling and highly skewed male: female ratios. In fact, so few animals were produced through reproduction, that most animals were imported from urban areas, providing an interesting opportunity to externally influence the population, control disease, and manage risk. Results from Study 2, indicate that land use by dogs is mostly concentrated within 200 meters of households and exhibits a notable diurnal pattern with dogs moving mostly during the day. Characterization of movement away from the house of origin (forays) found that dogs primarily use pastures to move with fewer visitations in continuous forest habitats including those in protected areas. Rivers appeared to present a barrier for dog movement; however, there were instances of them being crossed allowing access of dogs to protected lands. When moving in forest, dogs mostly used trails and roads. Finally, Study 3 determined that American mink interactions could potentially play a key role in CDV transmission and possibly persistence in this carnivore assemblage. Minks interacted frequently with otters at river otter latrines at intervals theoretically adequate for viable indirect transmission of CDV. As expected, dogs were rare in otter habitats; but dogs were seen interacting with American mink (killings or harassment) near households. Thus, mink in this system were acting as a potential `bridge host' between dog and otter populations. In addition, a high percentage of dogs and mink had serological evidence of exposure to CDV making the potential disease transfer risk to otters real. Altogether, this dissertation provides important information about the drivers of carnivore interactions related to disease risk in a multi-carnivore system. These interactions are not random, but rather they are driven by behavior both on the part of humans and their use and management of dogs, as well as by species-specific movement and territorial behaviors. Understanding rural dog's use and management by farmers and how dogs move on the landscape will also provide useful information to improve the integrated management of dog-wildlife interactions around protected lands. This will be important for the management not only of direct and indirect conflict, but also of disease risk in an apparent CDV reservoir in this natural ecosystem. Particularly interesting, the recent invasion of the American mink further complicates interaction risk as their movements on the landscape alter the carnivore community composition and, therefore, interactions among populations. This new population of mink may even provide sufficient population density in this ecosystem to allow persistence of CDV and other diseases that would otherwise outstrip its host population and collapse. This question of how introduced species alter population interactions in the context of disease transmission risk is poorly understood and bears future research. Altogether, the work presented in this dissertation shows the importance of incorporating human drivers in the management of conservation areas. In this system, understanding human management and use of dogs, dog movements on the landscape, and how human-introduced invasive species are changing multi-host pathogen dynamics are all critical factors in protecting threatened carnivores in the Valdivian Temperate Forest.
  • Thumbnail Image
    Item
    Interactions of Ethylene Oxide-Propylene Oxide Block Copolymers with Lipid Bilayers
    (2019-08) Zhang, Wenjia
    Nonionic poly(propylene oxide)-b-poly(ethylene oxide) (PPO-PEO) block copolymers, known as Pluronics or poloxamers, have been widely studied for their great potential in cell membrane stabilization and permeabilization due to their amphiphilicity and biocompatibility. A hydrophilic dominant commercial poloxamer P188 shows a reasonable stabilization effect in vivo on dystrophic muscle cell membranes. Despite recent advances made in this field, the structure-function relationships and the underlying mechanism of polymer protection are not fully understood. The goals of this dissertation are to understand the fundamental mechanism of polymer-membrane association and to further design effective polymers to improve the therapeutic approach of cell membrane stabilization for Duchenne muscular dystrophy. Herein, we developed a simple yet powerful method that enables the quantification of the relatively weak interactions between the copolymers and vesicular lipid bilayers based on distinct diffusivity of free and bound polymers, using pulsed-field-gradient NMR (PFG-NMR). This is the first quantitative study that systematically investigated polymer binding to lipid membranes in the literature to our knowledge, which provides direct evidence regarding how polymer structure and membrane composition and curvature dictate their interactions. With lab-synthesized PPO-PEO diblock analogs as complements to the commercial triblock poloxamers, we found that polymers with larger molecular weight and higher hydrophobicity result in stronger polymer-membrane association. Also, the lipid bilayer composition plays a critical role. Notably, polymer binding drops 10-fold in a universal fashion as cholesterol concentration in the bilayer increases from 0 to 30 mol.%. Switching the lipid headgroup from choline to glycerol significantly enhanced polymer binding. Additionally, polymer protection efficacy on liposomes against induced lipid peroxidation was assessed and compared with their stabilization efficacy in vitro and in vivo.
  • Thumbnail Image
    Item
    Interactions of Fusarium virguliforme with Other Common Soybean Root Pathogens and the Soybean Aphid
    (2020-08) Geske, Alissa
    Many diseases reduce soybean (Glycine max) yield every year, with root diseases often having the greatest impacts on yield in the Midwestern U.S. One important root pathogen of soybean is Fusarium virguliforme (Fv), the causal agent of sudden death syndrome (SDS). Even though soybean plants displaying SDS symptoms are commonly attacked by multiple fungal pathogens and insects, it is unknown how interactions between Fv and other attackers may alter SDS disease development and soybean growth. In our first study, we examined potential interactions between Fv and other common soybean root pathogens including F. acuminatum, F. oxysporum, F. solani, and Clonostachys rosea. Interactions were assessed in vitro and in soybean plants to evaluate their effect on SDS disease development and soybean growth. Results from the in vitro studies suggest that the growth of Fv was not affected by any of these fungi, but the growth of F. acuminatum and F. oxysporum isolates was reduced in the presence of Fv. Further results suggest that coinfection of soybean with Fv and C. rosea and Fv and F. solani can reduce SDS foliar disease severity and that coinfection of soybean with Fv and F. oxysporum and Fv and F. acuminatum can increase SDS foliar severity compared to the Fv-only treatment under growth chamber conditions. Coinfections of soybean with Fv and all eight fungal test isolates individually did not increase or decrease levels of root rot or plant biomass compared to infection by Fv alone. In our second study, we examined potential interactions between Fv and the soybean aphid, Aphis glycines, in greenhouse, growth chamber, and field experiments to evaluate their effect on SDS disease development, aphid growth, and soybean growth. Overall, the results suggest that Fv and soybean aphids have minimal to no interaction with one another while co-occurring on soybean when SDS develops to low levels, as was the case in these studies. There was no clear effect of soybean aphid herbivory on SDS foliar or root disease development in these studies nor did we detect a clear effect of combined soybean aphid herbivory and Fv infection on soybean growth. To our knowledge this is the first investigation into potential interactions between Fv and other common root pathogens and Fv and the soybean aphid.