Browsing by Author "Hopkins, Skylar R."

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    Continued preference for suboptimal habitat reduces bat survival with white-nose syndrome
    Hopkins, Skylar R.; Hoyt, Joseph R.; White, J. Paul; Kaarakka, Heather M.; Redell, Jennifer A.; DePue, John E.; Scullon, William H.; Kilpatrick, A. Marm; Langwig, Kate E. (Springer Nature, 2021)
    Habitat alteration can influence suitability, creating ecological traps where habitat preference and fitness are mismatched. Despite their importance, ecological traps are notoriously difficult to identify and their impact on host–pathogen dynamics remains largely unexplored. Here we assess individual bat survival and habitat preferences in the midwestern United States before, during, and after the invasion of the fungal pathogen that causes white-nose syndrome. Despite strong selection pressures, most hosts continued to select habitats where disease severity was highest and survival was lowest, causing continued population declines. However, some individuals used refugia where survival was higher. Over time, a higher proportion of the total population used refugia than before pathogen arrival. Our results demonstrate that host preferences for habitats with high disease-induced mortality can create ecological traps that threaten populations, even in the presence of accessible refugia.
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    A global parasite conservation plan
    Carlson, Colin J.; Hopkins, Skylar R.; Bell, Kayce C.; Dona, Jorge; Godfrey, Stephanie S.; Kwak, Mackenzie L.; Lafferty, Kevin D.; Moir, Melinda L.; Speer, Kelly A.; Strona, Giovanni; Torchin, Mark; Wood, Chelsea L. (2020-10)
    Found throughout the tree of life and in every ecosystem, parasites are some of the most diverse, ecologically important animals on Earth-but in almost all cases, the least protected by wildlife or ecosystem conservation efforts. For decades, ecologists have been calling for research to understand parasites' important ecological role, and increasingly, to protect as many species from extinction as possible. However, most conservationists still work within priority systems for funding and effort that exclude or ignore parasites, or treat parasites as an obstacle to be overcome. Our working group identified 12 goals for the next decade that could advance parasite biodiversity conservation through an ambitious mix of research, advocacy, and management.
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    Host community composition and defensive symbionts determine trematode parasite abundance in host communities
    Hopkins, Skylar R.; Ocampo, Jancarla M.; Wojdak, Jeremy M.; Belden, Lisa K. (ESA, 2016-03-29)
    Host species vary in their propensity to become infected by and transmit parasites, and this variation in host competency can influence parasite transmission within host communities. Host competency is often attributed to morphological, physiological, and behavioral defenses of hosts, but hosts commonly have an additional, lesser studied form of protection: defensive symbionts. For instance, snails are facultatively defended by ectosymbiotic oligochaete worms (Chaetogaster limnaei) that consume free-living trematode parasites, bacteria protect amphibians from the fungus that causes chytridiomycosis, and ants protect plants from herbivores. In addition to reducing infection on their hosts, defensive symbionts may influence parasite transmission to other hosts by redirecting parasites toward other hosts and/or removing parasites from the system. We explored these possibilities by examining the relative roles of community composition and the presence of defensive symbionts (C. limnaei) in determining trematode infection intensity among second intermediate host communities composed of snails (Helisoma trivolvis) and tadpoles (Rana catesbeiana). Parasites were dramatically more successful at infecting snails than tadpoles, which led to more total parasites in host communities where snails were present. In addition, defensive symbionts substantially reduced snail infection intensity and thus reduced the total number of parasites in communities containing symbiont-defended snail hosts. Neither host community composition nor the presence of defensive symbionts on snails influenced individual tadpole infection in our experiments. Therefore, in our experiments, second intermediate host community structure did not influence individual host tadpole infection risk, but did influence total parasite transmission.
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    Multi-scale Transmission Ecology: How Individual Host Characteristics, Host Population Density, and Community Structure Influence Transmission in a Multi-host Snail Symbiont System
    Hopkins, Skylar R. (Virginia Tech, 2017-05-04)
    We live in an era of global change, where emerging infectious diseases such as Ebola, Zika, bird flu, and white nose syndrome are affecting humans, wildlife, and domesticated species at an increasing rate. To understand and predict the dynamic spread of these infectious agents and other symbionts through host populations and communities, we need dynamic mathematical models that accurately portray host-symbiont transmission. But transmission is an inherently difficult process to measure or study, because it is actually a series of interacting processes influenced by abiotic and biotic factors at multiple scales, and thus empirical tests of the transmission function within epidemiological models are rare. Therefore, in this dissertation, I explore factors at the individual, population, and community-levels that influence host contact rates or symbiont transmission success in a common snail-symbiont system, providing a detailed description of the multi-faceted nature of symbiont transmission. From a review of the ecological literature, I found that most models assume that transmission is a linear function of host population density, whereas most empirical studies describe transmission as a nonlinear function of density. I then quantified the net nonlinear transmission-density relationship in a system where ectosymbiotic oligochaetes are directly transmitted among snail hosts, and I explored the ecological mechanisms underlying the nonlinear transmission-density relationship observed in the field via intraspecific transmission success and contact rate experiments in the laboratory. I found that the field results could be explained by heterogeneity in transmission success among snails with different characteristics and nonlinear contact-density relationships caused by non-instantaneous handling times. After I 'unpacked'population-level transmission dynamics into those individual-level mechanistic processes, I used this same approach to examine higher-level ecological organization by describing the mechanistic underpinnings of interspecific or community-level transmission in the same snail-symbiont system. I found that low interspecific transmission rates in the field were the product of opposing interactions between high population densities, high prevalences of infection, and very low interspecific transmission success caused by strong symbiont preferences for their current host species. Unpacking transmission in this way resulted in one of the most detailed empirical studies of transmission dynamics in a wildlife system, and yielded many surprising new insights in symbiont ecology that would not have been discovered with a purely phenomenological or holistic view of transmission. Though simple, linear, and holistic epidemiological models will always be important tools in disease ecology, 'unpacking'transmission rates and adding heterogeneity and nonlinearity to models, as I have done here, will become increasingly important as we work to maximize model prediction accuracy in this era of increased disease emergence.
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    Parasite predators exhibit a rapid numerical response to increased parasite abundance and reduce transmission to hosts
    Hopkins, Skylar R.; Wyderko, Jennie A.; Sheehy, Robert R.; Belden, Lisa K.; Wojdak, Jeremy M. (Wiley, 2013-05-09)
    Predators of parasites have recently gained attention as important parts of food webs and ecosystems. In aquatic systems, many taxa consume free-living stages of parasites, and can thus reduce parasite transmission to hosts. However, the importance of the functional and numerical responses of parasite predators to disease dynamics is not well understood. We collected host–parasite–predator cooccurrence data from the field, and then experimentally manipulated predator abundance, parasite abundance, and the presence of alternative prey to determine the consequences for parasite transmission. The parasite predator of interest was a ubiquitous symbiotic oligochaete of mollusks, Chaetogaster limnaei limnaei, which inhabits host shells and consumes larval trematode parasites. Predators exhibited a rapid numerical response, where predator populations increased or decreased by as much as 60% in just 5 days, depending on the parasite:predator ratio. Furthermore, snail infection decreased substantially with increasing parasite predator densities, where the highest predator densities reduced infection by up to 89%. Predators of parasites can play an important role in regulating parasite transmission, even when infection risk is high, and especially when predators can rapidly respond numerically to resource pulses. We suggest that these types of interactions might have cascading effects on entire disease systems, and emphasize the importance of considering disease dynamics at the community level.
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    Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission
    Wood, Chelsea L.; Sokolow, Susanne H.; Jones, Isabel J.; Chamberlin, Andrew J.; Lafferty, Kevin D.; Kuris, Armand M.; Jocque, Merlijn; Hopkins, Skylar R.; Adams, Grant; Buck, Julia C.; Lund, Andrea J.; Garcia-Vedrenne, Ana E.; Fiorenza, Evan; Rohr, Jason R.; Allan, Fiona; Webster, Bonnie; Rabone, Muriel; Webster, Joanne P.; Bandagny, Lydie; Ndione, Raphael; Senghor, Simon; Schacht, Anne-Marie; Jouanard, Nicolas; Riveau, Gilles; De Leo, Giulio A. (2019-11-12)
    Recently, the World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. We sought to identify robust indicators that would enable precision targeting of these snails. At the site of the world's largest recorded schistosomiasis epidemic-the Lower Senegal River Basin in Senegal-intensive sampling revealed positive relationships between intermediate host snails (abundance, density, and prevalence) and human urogenital schistosomiasis reinfection (prevalence and intensity in schoolchildren after drug administration). However, we also found that snail distributions were so patchy in space and time that obtaining useful data required effort that exceeds what is feasible in standard monitoring and control campaigns. Instead, we identified several environmental proxies that were more effective than snail variables for predicting human infection: the area covered by suitable snail habitat (i.e., floating, nonemergent vegetation), the percent cover by suitable snail habitat, and size of the water contact area. Unlike snail surveys, which require hundreds of person-hours per site to conduct, habitat coverage and site area can be quickly estimated with drone or satellite imagery. This, in turn, makes possible large-scale, high-resolution estimation of human urogenital schistosomiasis risk to support targeting of both mass drug administration and snail control efforts.