Many parasites have external transmission stages that persist in the environment prior to infecting a new host. Understanding how long these stages can persist, and how abiotic conditions such as temperature affect parasite persistence, is important for predicting infection dynamics and parasite responses to future environmental change. In this study, we explored environmental persistence and thermal tolerance of a debilitating protozoan parasite that infects monarch butterflies. Parasite transmission occurs when dormant spores, shed by adult butterflies onto host plants and other surfaces, are later consumed by caterpillars. We exposed parasite spores to a gradient of ecologically-relevant temperatures for 2, 35, or 93 weeks. We tested spore viability by feeding controlled spore doses to susceptible monarch larvae, and examined relationships between temperature, time, and resulting infection metrics. We also examined whether distinct parasite genotypes derived from replicate migratory and resident monarch populations differed in their thermal tolerance. Finally, we examined evidence for a trade-off between short-term within-host replication and long-term persistence ability. Parasite viability decreased in response to warmer temperatures over moderate-to-long time scales. Individual parasite genotypes showed high heterogeneity in viability, but differences did not cluster by migratory vs. resident monarch populations. We found no support for a negative relationship between environmental persistence and within-host replication, as might be expected if parasites invest in short-term reproduction at the cost of longer-term survival. Findings here indicate that dormant spores can survive for many months under cooler conditions, and that heat dramatically shortens the window of transmission for this widespread and virulent butterfly parasite.
Sánchez CA, Ragonese IG, de Roode JC, Altizer S. Thermal tolerance and environmental persistence of a protozoan parasite in monarch butterflies. Journal of Invertebrate Pathology. 2021 Feb 11:107544. https://doi.org/10.1016/j.jip.2021.107544
Check out the new book chapter by OSE student Mike Newberry and recent OSE graduate Dr. Michelle Evans!
Evans, M., Newberry, Philip M., and Courtney C. Murdock. “Carry-over Effects of the Larval Environment” inPopulation Biology of Vector-Borne Diseases. Editors: Drake JM, Bonsall M, Strand M. Oxford University Press; 2020 Dec 30. 155-174.
Populations of cold‐adapted species at the trailing edges of geographic ranges are particularly vulnerable to the negative effects of climate change from the combination of exposure to warm temperatures and high sensitivity to heat. Many of these species are predicted to decline under future climate scenarios, but they could persist if they can adapt to warming climates either physiologically or behaviourally. We aim to understand local variation in contemporary habitat use and use this information to identify signs of adaptive capacity. We focus on moose (Alces alces), a charismatic species of conservation and public interest.
The northeastern United States, along the trailing edge of the moose geographic range in North America.
We compiled data on occurrences and habitat use of moose from remote cameras and GPS collars across the northeastern United States. We use these data to build habitat suitability models at local and regional spatial scales and then to predict future habitat suitability under climate change. We also use fine‐scale GPS data to model relationships between habitat use and temperature on a daily temporal scale and to predict future habitat use.
We find that habitat suitability for moose will decline under a range of climate change scenarios. However, moose across the region differ in their use of climatic and habitat space, indicating that they could exhibit adaptive capacity. We also find evidence for behavioural responses to weather, where moose increase their use of forested wetland habitats in warmer places and/or times.
Our results suggest that there will be significant shifts in moose distribution due to climate change. However, if there is spatial variation in thermal tolerance, trailing‐edge populations could adapt to climate change. We highlight that prioritizing certain habitats for conservation (i.e., thermal refuges) could be crucial for this adaptation.
Teitelbaum CS, Sirén AP, Coffel E, Foster JR, Frair JL, Hinton JW, Horton RM, Kramer DW, Lesk C, Raymond C, Wattles DW. Habitat use as indicator of adaptive capacity to climate change. Diversity and Distributions. 2021. https://doi.org/10.1111/ddi.13223
Pacific salmon spawning and rearing habitats result from dynamic interactions among geomorphic processes, natural disturbances, and hydro‐climatological factors acting across a range of spatial and temporal scales. We used a 21‐year record of redd locations in a wilderness river network in central Idaho, USA, to examine which covariates best predict the spawning occurrence of Chinook Salmon Oncorhynchus tshawytscha and how shifts under a changing climate might affect habitat availability. We quantified geomorphic characteristics (substrate size, channel slope, and valley confinement), climatic factors (stream temperature and summer discharge), wildfire, and conspecific abundance (as inferred by the number of redds) throughout the network. We then built and compared logistic regression models that estimated redd occurrence probability as a function of these covariates in 1‐km reaches throughout the network under current and projected climate change scenarios. Redd occurrence was strongly affected by nearly all of the covariates examined. The best models indicated that climate‐driven changes in redd occurrence probabilities will be relatively small but spatially heterogeneous, with warmer temperatures increasing occurrence probabilities in cold, high‐elevation reaches and decreasing probabilities in warm, low‐elevation reaches. Furthermore, positive effects of wildfire on redd occurrence may be more important than climate‐driven effects on stream temperature and summer discharge, although climate‐related changes in temperature and scour regime during the egg incubation period may influence survival to emergence. Our results identify where favorable spawning habitats are likely to exist under climate change, how future habitat distributions may differ from contemporary conditions, and where habitat conservation might be prioritized. Furthermore, the positive occurrence–abundance relationship we observed indicates that the study site is underseeded, and effective management actions are needed for increasing the recruitment of spawning adults to take advantage of available habitat.
Jacobs GR, Thurow RF, Buffington JM, Isaak D, Wenger SJ. Climate, Fire Regime, Geomorphology, and Conspecifics Influence the Spatial Distribution of Chinook Salmon Redds. Transactions of the American Fisheries Society. 2020.
Resident species can facilitate invading species (biotic assistance) or inhibit their expansion (biotic resistance). Species interactions are often context‐dependent and the relative importance of biotic assistance versus resistance could vary with abiotic conditions or the life stage of the invading species, as invader stress tolerances and resource requirements change with ontogeny. In northeast Florida salt marshes, the abundant dead litter (wrack) of the native marsh cordgrass, Spartina alterniflora, could influence the expansion success of the black mangrove, Avicennia germinans, a tropical species that is expanding its range northward.
We used two field experiments to examine how S. alterniflora wrack affects A. germinans success during (a) propagule establishment and (b) subsequent seedling survival. We also conducted laboratory feeding assays to identify propagule consumers and assess how wrack presence influences herbivory on mangrove propagules.
Spartina alterniflora wrack facilitated A. germinans establishment by promoting propagule recruitment, retention and rooting; the tidal regime influenced the magnitude of these effects. However, over time S. alterniflora wrack inhibited A. germinans seedling success by smothering seedlings and attracting herbivore consumers. Feeding assays identified rodents—which seek refuge in wrack—as consumers of A. germinans propagules.
Synthesis. Our results suggest that the deleterious effects of S. alterniflora wrack on A. germinans seedling survival counterbalance the initial beneficial effects of wrack on A. germinans seed establishment. Such seed‐seedling conflicts can arise when species stress tolerances and resource requirements change throughout development and vary with abiotic conditions. In concert with the tidal conditions, the relative importance of positive and negative interactions with wrack at each life stage can influence the rate of local and regional mangrove expansion. Because interaction strengths can change in direction and magnitude with ontogeny, it is essential to examine resident–invader interactions at multiple life stages and across environmental gradients to uncover the mechanisms of biotic assistance and resistance during invasion.
Smith RS, Blaze JA, Byers JE. Dead litter of resident species first facilitates and then inhibits sequential life stages of range‐expanding species. Journal of Ecology. https://doi.org/10.1111/1365-2745.13586
Mobile animals transport nutrients and propagules across habitats, and are crucial for the functioning of food webs and for ecosystem services. Human activities such as urbanization can alter animal movement behavior, including site fidelity and resource use. Because many urban areas are adjacent to natural sites, mobile animals might connect natural and urban habitats. More generally, understanding animal movement patterns in urban areas can help predict how urban expansion will affect the roles of highly mobile animals in ecological processes.
Here, we examined movements by a seasonally nomadic wading bird, the American white ibis (Eudocimus albus), in South Florida, USA. White ibis are colonial wading birds that forage on aquatic prey; in recent years, some ibis have shifted their behavior to forage in urban parks, where they are fed by people. We used a spatial network approach to investigate how individual movement patterns influence connectivity between urban and non-urban sites. We built a network of habitat connectivity using GPS tracking data from ibis during their non-breeding season and compared this network to simulated networks that assumed individuals moved indiscriminately with respect to habitat type.
We found that the observed network was less connected than the simulated networks, that urban-urban and natural-natural connections were strong, and that individuals using urban sites had the least-variable habitat use. Importantly, the few ibis that used both urban and natural habitats contributed the most to connectivity.
Habitat specialization in urban-acclimated wildlife could reduce the exchange of propagules and nutrients between urban and natural areas, which has consequences both for beneficial effects of connectivity such as gene flow and for detrimental effects such as the spread of contaminants or pathogens.
Claire S. Teitelbaum, Jeffrey Hepinstall-Cymerman, Anjelika Kidd-Weaver, Sonia M. Hernandez, Sonia Altizer, Richard J. Hall. Urban specialization reduces habitat connectivity by a highly mobile wading bird. Movement Ecology8, 49 (2020). https://doi.org/10.1186/s40462-020-00233-7
Check out OSE graduate student Laura Kojima on the November 2020 episode of Ologies by Allie Ward. Listen here. Way to be an amazing science communicator, Laura! To see more of Laura, check out her social media on Twitter and Instagram.
Our very own Kaylee Arnold won best talk for her presentation, “The gut microbial diversity of a Chagas disease vector varies across coinfection status throughout central Panama” in the Medical, Urban, & Veterinary Entomology section of the Entomological Society of America at their annual meeting. Read below for her abstract. Congratulations, Kaylee!
Chagas disease is caused by the parasite Trypanosoma cruzi that is carried in the guts of hematophagous triatomine vectors. Triatomines are often coinfected with the parasite T. rangeli, which is non-pathogenic to mammals but can reduce fitness of their triatomine hosts. This study examined the gut microbial diversity of T. cruzi infected, coinfected, and uninfected triatomines (n = 288) throughout central Panama. We hypothesized that single and coinfected triatomines would have greater gut microbial diversity than uninfected individuals due to pathogen-microbe interactions within the gut, which can facilitate the proliferation of less dominant bacterial taxa.
Coinfections were found in 13% of individuals (40/288) and there was significantly greater alpha diversity in coinfected individuals when compared to both single and uninfected samples (Dunn’s test of multiple comparisons, p < 0.001). Furthermore, single T. cruzi infections were found in 34% of sampled individuals (91/288) and also displayed significantly greater alpha diversity when compared to uninfected individuals (Kruskal-Wallis H test, p < 0.001). Across all samples, Sphingomonas was the most dominant taxa, and decreased in relative abundance compared to uninfected individuals. Finally, the beta diversity across infected samples was significantly different compared to uninfected samples (PERMANOVA p = 0.001 using Bray-Curtis dissimilarity). These results highlight patterns of microbial diversity which may be impacted by vector infection status and will be important to consider when developing vector control strategies.
Congratulations, Lexi! Here is the abstract of her thesis, entitled Invertebrate herbivory of understory trees in the Georgia Piedmont in response to soil warming:
As the global mean surface temperature increases, changes in biogeochemical cycling have the potential to have cascading effects on plant and invertebrate interactions. Previous warming studies have primarily been conducted in recently glaciated, more fertile soils, and the response of plant and invertebrate interactions to warming is unclear in lower latitude, less fertile soils of the Georgia Piedmont. In this study, I examined leaf and soil chemistry (%N, C:N) and herbivore damage (% leaf area consumed) from understory tree seedlings of the Georgia Piedmont. Carbon and nitrogen foliar content and invertebrate herbivory did not respond to warming in any year, but there were interactive effects of temperature and species. Overall, warming did not have an indirect effect on plant-herbivore interactions, which is likely due to Piedmont soils containing less available nitrogen. However, species-level variation in response to warming has implications for forest composition changes.