Effects of environmental change on emerging parasitic diseases

Ecological disturbances exert an influence on the emergence and proliferation of malaria and zoonotic parasitic diseases, including, Leishmaniasis, cryptosporidiosis, giardiasis, trypanosomiasis, schistosomiasis, filariasis, onchocerciasis, and loiasis. Each environmental change, whether occurring as a natural phenomenon or through human intervention, changes the ecological balance and context within which disease hosts or vectors and parasites breed, develop, and transmit disease. Each species occupies a particular ecological niche and vector species sub-populations are distinct behaviourally and genetically as they adapt to man-made environments. Most zoonotic parasites display three distinct life cycles: sylvatic, zoonotic, and anthroponotic. In adapting to changed environmental conditions, including reduced non-human population and increased human population, some vectors display conversion from a primarily zoophyllic to primarily anthrophyllic orientation. Deforestation and ensuing changes in landuse, human settlement, commercial development, road construction, water control systems (dams, canals, irrigation systems, reservoirs), and climate, singly, and in combination have been accompanied by global increases in morbidity and mortality from emergent parasitic disease. The replacement of forests with crop farming, ranching, and raising small animals can create supportive habitats for parasites and their host vectors. When the land use of deforested areas changes, the pattern of human settlement is altered and habitat fragmentation may provide opportunities for exchange and transmission of parasites to the heretofore uninfected humans. Construction of water control projects can lead to shifts in such vector populations as snails and mosquitoes and their parasites. Construction of roads in previously inaccessible forested areas can lead to erosion, and stagnant ponds by blocking the flow of streams when the water rises during the rainy season. The combined effects of environmentally detrimental changes in local land use and alterations in global climate disrupt the natural ecosystem and can increase the risk of transmission of parasitic diseases to the human population.     

Gimme shelter – the relative sensitivity of parasitic nematodes with direct and indirect life cycles to climate change

Climate change is expected to alter the dynamics of host–parasite systems globally. One key element in developing predictive models for these impacts is the life cycle of the parasite. It is, for example, commonly assumed that parasites with an indirect life cycle would be more sensitive to changing environmental conditions than parasites with a direct life cycle due to the greater chance that at least one of their obligate host species will go extinct. Here, we challenge this notion by contrasting parasitic nematodes with a direct life cycle against those with an indirect life cycle. Specifically, we suggest that behavioral thermoregulation by the intermediate host may buffer the larvae of indirectly transmitted parasites against temperature extremes, and hence climate warming. We term this the ‘shelter effect’. Formalizing each life cycle in a comprehensive model reveals a fitness advantage for the direct life cycle over the indirect life cycle at low temperatures, but the shelter effect reverses this advantage at high temperatures. When examined for seasonal environments, the models suggest that climate warming may in some regions create a temporal niche in mid‐summer that excludes parasites with a direct life cycle, but allows parasites with an indirect life cycle to persist. These patterns are amplified if parasite larvae are able to manipulate their intermediate host to increase ingestion probability by definite hosts. Furthermore, our results suggest that exploiting the benefits of host sheltering may have aided the evolution of indirect life cycles. Our modeling framework utilizes the Metabolic Theory of Ecology to synthesize the complexities of host behavioral thermoregulation and its impacts on various temperature‐dependent parasite life history components in a single measure of fitness, R₀. It allows quantitative predictions of climate change impacts, and is easily generalized to many host–parasite systems.     

Life history and parasites of the invasive mosquitofish (Gambusia holbrooki) along a latitudinal gradient

The eastern mosquitofish (Gambusia holbrooki) is among the most invasive fish worldwide and yet, while very abundant in most Mediterranean countries, it is unable to tolerate the colder winters of northern and central Europe. Understanding the effects of latitude on its life-history traits is essential to predict the potential for its invasion of central Europe in current scenarios of climate change. We studied the variation of life-history traits and parasite load in the eastern mosquitofish along a latitudinal gradient from southern France to southern Spain, sampling mosquitofish populations in eight Mediterranean river mouths ranging 5° in latitude. Southern mosquitofish populations displayed higher catch rates, allocated more energy to reproduction (gonadosomatic index and gonadal weight after accounting for fish size) and had a lower condition (total weight and eviscerated weight after accounting for fish size) than in northern populations. Despite variability among populations, size-at-maturity (L₅₀) significantly varied with latitude and northern individuals matured at smaller size (lower L₅₀). Parasite prevalence ranged from 0.0 to 26.7% but parasite richness was very low; all the parasites identified were larvae of pleurocercoid cestodes belonging to the order Pseudophyllidea. The abundance of mosquitofish parasites decreased with latitude and the presence and number of parasites infecting the mosquitofish had a significant negative effect on fish condition. The significant effects of latitude on the catch rates, life history and parasites of mosquitofish highlight the importance of latitudinal studies of invasive species to understand the interactive mechanisms of climate change and biological invasions.     

Intensive Farming: Evolutionary Implications for Parasites and Pathogens

An increasing number of scientists have recently raised concerns about the threat posed by human intervention on the evolution of parasites and disease agents. New parasites (including pathogens) keep emerging and parasites which previously were considered to be 'under control' are re-emerging, sometimes in highly virulent forms. This re-emergence may be parasite evolution, driven by human activity, including ecological changes related to modern agricultural practices. Intensive farming creates conditions for parasite growth and transmission drastically different from what parasites experience in wild host populations and may therefore alter selection on various traits, such as life-history traits and virulence. Although recent epidemic outbreaks highlight the risks associated with intensive farming practices, most work has focused on reducing the short-term economic losses imposed by parasites, such as application of chemotherapy. Most of the research on parasite evolution has been conducted using laboratory model systems, often unrelated to economically important systems. Here, we review the possible evolutionary consequences of intensive farming by relating current knowledge of the evolution of parasite life-history and virulence with specific conditions experienced by parasites on farms. We show that intensive farming practices are likely to select for fast-growing, early-transmitted, and hence probably more virulent parasites. As an illustration, we consider the case of the fish farming industry, a branch of intensive farming which has dramatically expanded recently and present evidence that supports the idea that intensive farming conditions increase parasite virulence. We suggest that more studies should focus on the impact of intensive farming on parasite evolution in order to build currently lacking, but necessary bridges between academia and decision-makers.     

Seasonal dietary shifts enhance parasite transmission to lake salmonids during ice cover

Changes in abiotic and biotic factors between seasons in subarctic lake systems are often profound, potentially affecting the community structure and population dynamics of parasites over the annual cycle. However, few winter studies exist and interactions between fish hosts and their parasites are typically confined to snapshot studies restricted to the summer season whereas host‐parasite dynamics during the ice‐covered period rarely have been explored. The present study addresses seasonal patterns in the infections of intestinal parasites and their association with the diet of sympatric living Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) in Lake Takvatn, a subarctic lake in northern Norway. In total, 354 Arctic charr and 203 brown trout were sampled from the littoral habitat between June 2017 and May 2018. Six trophically transmitted intestinal parasite taxa were identified and quantified, and their seasonal variations were contrasted with dietary information from both stomachs and intestines of the fish. The winter period proved to be an important transmission window for parasites, with increased prevalence and intensity of amphipod‐transmitted parasites in Arctic charr and parasites transmitted through fish prey in brown trout. In Arctic charr, seasonal patterns in parasite infections resulted mainly from temporal changes in diet toward amphipods, whereas host body size and the utilization of fish prey were the main drivers in brown trout. The overall dynamics in the community structure of parasites chiefly mirrored the seasonal dietary shifts of their fish hosts.     

Transmission of parasites in the coastal waters of the Arctic seas and possible effect of climate change

The review deals with the biodiversity, life cycles, distribution and temperature adaptations of parasites circulating in the coastal waters of northern polar seas. Special attention is given to helminths of marine birds, which are the most common parasites in the coastal waters. Among them, the focus is on trematodes. Factors responsible for the impoverished species composition of parasites in the Arctic are analyzed. It is shown that species without free-living larvae in the life cycle have an advantage in this environment. The abundance of cestodes and acanthocephalans in Arctic seabirds is linked with the high proportion of crustaceans in their diet. The phenomenon of nonspecific parasitism (occurrence of parasites in atypical host species) is analyzed from an evolutionary viewpoint. Characteristic features in the spatial distribution of infection of marine coastal invertebrates with parasite larvae are considered, and factors that determine it are specified. The prevalence of infection in intermediate hosts is closely connected with the abundance of final hosts, which makes it possible to estimate the abundance of final hosts in a given region and reveal trends in its changes. Trematodes have a high potential for temperature acclimation. This facilitates their transmission in the northern seas but, on the other hand, makes it unlikely that the transmission process would be intensified upon an increase in summer temperatures resulting from climate warming. However, intensification of transmission may well occur due to the prolongation of the warm season (“transmission window”), which has been predicted and is already observed. It is suggested that warming in the Arctic promotes both the entry of certain “southern” species into the Arctic and the trans-Arctic interpenetration of the North Atlantic and North Pacific parasitic faunas. A case is made for the necessity to broaden the scope of parasitological research in the Arctic and Subarctic, including parasitological monitoring at the reference sites of the sea coast.     

Yield stability: an agronomic perspective on the origin of Near Eastern agriculture

Here we argue that, based on evolutionary, ecological and agronomic considerations, climate change could not have been a suitable background nor a probable cause of plant domestication in the Near East. This thesis is developed based on the year-to-year yield dynamics in traditional rainfed grain farming in semi-arid environments, on the genetic basis that underlies temporal yield dynamics in natural wild cereal populations as well as in traditional farming systems, and upon the recognition that prior to elaborate high capacity and long-range trade networks, yield stability was more important than yield maximization. We also briefly discuss the likely social and cultural responses to subtle and real climatic changes vs. responses to rapid directional environmental trends. Taking into account the agronomic, ecological and genetic aspects discussed, it is suggested that the Near Eastern founder crop assemblage was chosen to function within the normal east Mediterranean precipitation regime, in which good rainy years create the ‘normal surplus’ that sustains farming communities during drought years, and the different crop types provide the system with its compensating ability. A slow (but real) climatic change is unlikely to induce major (revolutionary) cultural changes. Nor would a prominent environmental change provide the proper background for the origins of agriculture because it would abolish the buffering capacity of the system. Therefore, farming cannot function as a sustainable ‘buffering mechanism’ to counterbalance climatic instability causing natural resource depletion.     

Infection dynamics of Cichlidogyrus tilapiae and C. sclerosus (Monogenea, Ancyrocephalinae) in Nile tilapia (Oreochromis niloticus L.) from Uganda

The infection dynamics of the gill monogeneans Cichlidogyrus tilapiae and C. sclerosus on Oreochromis niloticus with respect to habitat type (reservoir, stream, ponds and cages), host sex, size and seasons was determined between January and November 2008. During the study period, 45.2% of the 650 fish examined were infected with Cichlidogyrus spp. The infected hosts harboured an average of 8.6 ± 3.4 parasites/fish. Across habitat types, the proportion of infected fish was not statistically different. In contrast, the number of parasites recorded on infected fish from different habitat types differed significantly. The highest parasite number was recorded in reservoir-dwelling fish and lowest in stream-dwelling hosts. Concerning sex, more female O. niloticus were infected and harboured a high number of parasites than male and sexually undifferentiated fish. A weak negative relationship was found between rainfall and monthly parasite infections. However, a higher number of parasites and proportion of infected hosts were found during dry than in wet seasons, except in ponds. Results of this study show that differential exposure due to changes in fish behaviour associated with habitat modification and sex may account for the infection difference across the sampled sites. Meanwhile, rainfall and the associated hydrological events are important factors regulating monogenean infections in tropical aquatic environments. The continuous presence of Cichlidogyrus spp. in fish provides evidence of possible parasite outbreaks, indicating the application of biosecurity measures as crucial for the success of intensive fish farming.     

Parasitic anomalies observed in snow trout due to anthropogenic stress in water bodies

There is interrelationship of the environmental conditions and fish health. Decrease or increase of pollution in aquatic ecosystem have direct impact on presence or absence of parasites. Fish living under optimum environmental, well-nourished conditions are more resistant to diseases than fish weakened by malnutrition caused by parasite infestation or due to deterioration of environmental conditions because ofpollution. Fish encounters common parasites in wild and in culture systems. Parasites attach to the host through suckers and hooks and make their way inside the host through different means, which include skin, through mouth along with food, by means of gills. The hosts were collected during Jan 2019 to Jan 2020 from river Veshaw. During this study it was observed that presence of parasites causes some changes in fish which can serve as indicators of deterioration in aquatic habitat. Clinical signs were noticed in fish hosts collected from sites which received waste due to anthropogenic activities. Parasitic anomalies in the host collected from polluted site was observed to include body deformaties, gastric distention, lesions in gut, increased mucus production, damage in gill filaments etc.     

Impacts of co-occurring environmental changes on Alaskan stream fishes

1. Freshwater fishes are now facing unprecedented environmental changes across their northern ranges, especially due to rapid warming occurring at higher latitudes. However, empirical research that examines co-occurring environmental effects on northern fish communities remains limited.
2. We used fish community data from 1587 Alaskan stream sites to examine the potential combined and interacting effects of climate change, current weather, habitat, land use, and fire on two community-level metrics (species richness, relative abundance), and on the distributions of three Alaskan fish species.
3. Our models were 71–76% accurate in predicting the distribution of Alaskan stream fishes using a combination of climate and habitat variables. In contrast to other freshwater ecosystems that are most threatened by land use pressures, we did not detect any evidence for the potential stress of anthropogenic land use or fire on stream fishes.
4. Warming temperatures increased overall community richness and abundance but produced differing responses at the species level. Juvenile salmon presence was positively associated with several climate variables including warmer spring and autumn temperatures and wetter summers. In comparison, warmer seasonal temperatures contributed to declines for northern-adapted species such as Arctic grayling and Dolly Varden.
5. This study highlights the overarching role of current and changing climate in regulating northern stream fish biodiversity. Although many fish species may benefit from climate change across their northern ranges, localised declines are likely to occur and may prove detrimental for communities with limited fishing portfolios. Climate change adaptation and mitigation strategies customised for rapidly changing northern ecosystems will play an essential role in preserving ecologically unique northern species.

     

History and heroes: the thermal niche of fishes and long-term lake ice dynamics

These perspectives on climate change come largely from two views, i.e. that of a fish and fisheries ecologist with an autecological interest and that of a limnologist interested in long-term dynamics and change. Ideas about the thermal niche evolved from the late F. E. J. Fry's (University of Toronto) paradigm of fish response to environmental factors and the late G. Evelyn Hutchinson's (Yale University) formalization of the niche concept. In contrast, ideas about climatic change and variability have been shaped by long-term observation records from lakes around the northern hemisphere. The history of each set of ideas, i.e. the thermal niche of fishes and learning from nature's long-term dynamics, is briefly reviewed in the context of climatic change.     

Effects of a hurricane on fish parasites

Hurricanes, also called tropical cyclones, can dramatically affect life along their paths, including a temporary losing or reducing in number of parasites of fishes. Hurricane Katrina in the northern Gulf of Mexico in August 2005 provides many examples involving humans and both terrestrial and aquatic animals and plants. Fishes do not provide much of an indicator of hurricane activity because most species quickly repopulate the area. Fish parasites, however, serve as a good indicator of the overall biodiversity and environmental health. The reasons for the noted absence or reduction of parasites in fishes are many, and specific parasites provide indications of different processes. The powerful winds can produce perturbations of the sediments harboring intermediate hosts. The surge of high salinity water can kill or otherwise affect low salinity intermediate hosts or free-living stages. Both can introduce toxicants into the habitat and also interfere with the timing and processes involved with host-parasite interrelationships. All these have had a major influence on fish parasite populations of fishes in coastal Mississippi, especially for those parasites incorporating intermediate hosts in their life cycles. The length of time for a parasite to become re-established can vary considerably, depending on its life cycle as well as the associated biota, habitat, and environmental conditions, and each parasite provides a special indicator of environmental health.     

Rainfall induces time-lagged changes in the proportion of tropical aquatic hosts infected with metazoan parasites

Rainfall serves as a powerful driving force, shifting temporal abundance and prevalence patterns in parasites and free-living aquatic organisms in tropical environments. However, there is a lack of sound evidence showing the temporal scales at which rainfall influences infection parameters of parasites in the tropics either directly by affecting the parasite life cycle or indirectly by modifying host population abundance. In the present study, we demonstrate that changes in rainfall patterns lead to changes in the proportion of infected hosts with several parasite species, causing immediate or lagged favourable conditions for an increase in levels of infection. However, the temporal scale of the influence of rainfall varied depending on the ecological characteristics of aquatic ecosystems. Despite the environmental heterogeneity and stochastic events (storms and hurricanes) which affect the study sites, the proportion of infected hosts shows frequency cycles on a yearly scale, suggesting that environmental changes are within the range of variability that naturally occur at the study sites. We propose that the incorporation of stochastic events into long-term predictive models is crucial for understanding the potential effects of global climate change on infection parameters of tropical parasites.     

Functional reorganization of marine fish nurseries under climate warming

While climate change is rapidly impacting marine species and ecosystems worldwide, the effects of climate warming on coastal fish nurseries have received little attention despite nurseries’ fundamental roles in recruitment and population replenishment. Here, we used a 26‐year time series (1987–2012) of fish monitoring in the Bay of Somme, a nursery in the Eastern English Channel (EEC), to examine the impacts of environmental and human drivers on the spatial and temporal dynamics of fish functional structure during a warming phase of the Atlantic Multidecadal Oscillation (AMO). We found that the nursery was initially dominated by fishes with r‐selected life‐history traits such as low trophic level, low age and size at maturity, and small offspring, which are highly sensitive to warming. The AMO, likely superimposed on climate change, induced rapid warming in the late 1990s (over 1°C from 1998 to 2003), leading to functional reorganization of fish communities, with a roughly 80% decline in overall fish abundance and increased dominance by K‐selected fishes. Additionally, historical overfishing likely rendered the bay more vulnerable to climatic changes due to increased dominance by fishing‐tolerant, yet climatically sensitive species. The drop in fish abundance not only altered fish functional structure within the Bay of Somme, but the EEC was likely impacted, as the EEC has been unable to recover from a regime shift in the late 1990s potentially, in part, due to failed replenishment from the bay. Given the collapse of r‐selected fishes, we discuss how the combination of climate cycles and global warming could threaten marine fish nurseries worldwide, as nurseries are often dominated by r‐selected species.     

Projected climate and land use change alter western blacklegged tick phenology,seasonal host‐seeking suitability and human encounter risk in California

Global environmental change is having profound effects on the ecology of infectious disease systems, which are widely anticipated to become more pronounced under future climate and land use change. Arthropod vectors of disease are particularly sensitive to changes in abiotic conditions such as temperature and moisture availability. Recent research has focused on shifting environmental suitability for, and geographic distribution of, vector species under projected climate change scenarios. However, shifts in seasonal activity patterns, or phenology, may also have dramatic consequences for human exposure risk, local vector abundance and pathogen transmission dynamics. Moreover, changes in land use are likely to alter human–vector contact rates in ways that models of changing climate suitability are unlikely to capture. Here we used climate and land use projections for California coupled with seasonal species distribution models to explore the response of the western blacklegged tick (Ixodes pacificus), the primary Lyme disease vector in western North America, to projected climate and land use change. Specifically, we investigated how environmental suitability for tick host‐seeking changes seasonally, how the magnitude and direction of changing seasonal suitability differs regionally across California, and how land use change shifts human tick‐encounter risk across the state. We found vector responses to changing climate and land use vary regionally within California under different future scenarios. Under a hotter, drier scenario and more extreme land use change, the duration and extent of seasonal host‐seeking activity increases in northern California, but declines in the south. In contrast, under a hotter, wetter scenario seasonal host‐seeking declines in northern California, but increases in the south. Notably, regardless of future scenario, projected increases in developed land adjacent to current human population centers substantially increase potential human–vector encounter risk across the state. These results highlight regional variability and potential nonlinearity in the response of disease vectors to environmental change.     

Life in the fast lane: Temperature,density and host species impact survival and growth of the fish ectoparasite Argulus foliaceus

With expanding human populations, the food sector has faced constant pressure to sustainably expand and meet global production demands. In aquaculture this frequently manifests in an animal welfare crisis, with fish increasingly farmed under high production, high stress conditions. These intense environments can result in fish stocks having a high susceptibility to infection, with parasites and associated disease one of the main factors limiting industry growth. Prediction of infection dynamics is key to preventative treatment and mitigation. Considering the climatic and technology driven changes facing aquaculture, an understanding of how parasites react across a spectrum of conditions is required. Here we assessed the impact of temperature, infection density and host species on the life history traits of Argulus foliaceus, a common palearctic fish louse, representative of a parasite group problematic in freshwater aquaculture and fisheries worldwide. Temperature significantly affected development, growth and survival; parasites hatched and developed faster at higher temperatures, but also experienced shorter lifespans when maintained off the host. At high temperatures, these parasites will likely experience a short generation time as their life history traits are completed more rapidly. A. foliaceus additionally grew faster on natural hosts and at lower infection densities. Ultimately such results contribute to prediction of population dynamics, aiding development of effective control to improve animal welfare and reduce industry loss.     

Life cycle assessment of corn grain and corn stover in the United States

Background, aim, and scope  The goal of this study is to estimate the county-level environmental performance for continuous corn cultivation of corn grain and corn stover grown under the current tillage practices for various corn-growing locations in the US Corn Belt. The environmental performance of corn grain varies with its farming location because of climate, soil properties, cropping management, etc. Corn stover, all of the above ground parts of the corn plant except the grain, would be used as a feedstock for cellulosic ethanol. Materials and methods  Two cropping systems are under investigation: corn produced for grain only without collecting corn stover (referred to as CRN) and corn produced for grain and stover harvest (referred to as CSR). The functional unit in this study is defined as dry biomass, and the reference flow is 1 kg of dry biomass. The system boundary includes processes from cradle to farm gate. The default allocation procedure between corn grain and stover in the CSR system is the system expansion approach. County-level soil organic carbon dynamics, nitrate losses due to leaching, and nitrogen oxide and nitrous oxide emissions are simulated by the DAYCENT model. Life cycle environmental impact categories considered in this study are total fossil energy use, climate change (referred to as greenhouse gas emissions), acidification, and eutrophication. Sensitivities on farming practices and allocation are included. Results  Simulations from the DAYCENT model predict that removing corn stover from soil could decrease nitrogen-related emissions from soil (i.e., N₂O, NO _x , and NO₃ ⁻ leaching). DAYCENT also predicts a reduction in the annual accumulation rates of soil organic carbon (SOC) with corn stover removal. Corn stover has a better environmental performance than corn grain according to all life cycle environmental impacts considered. This is due to lower consumption of agrochemicals and fuel used in the field operations and lower nitrogen-related emissions from the soil. Discussion  The primary source of total fossil energy associated with biomass production is nitrogen fertilizer, accounting for over 30% of the total fossil energy. Nitrogen-related emissions from soil (i.e., N₂O, NO _x , and NO₃ ⁻ leaching) are the primary contributors to all other life cycle environmental impacts considered in this study. Conclusions  The environmental performance of corn grain and corn stover varies with the farming location due to crop management, soil properties, and climate conditions. Several general trends were identified from this study. Corn stover has a lower impact than corn grain in terms of total fossil energy, greenhouse gas emissions, acidification, and eutrophication. Harvesting corn stover reduces nitrogen-related emissions from the soil (i.e., N₂O, NO _x , NO₃ ⁻). The accumulation rate of soil organic carbon is reduced when corn stover is removed, and in some cases, the soil organic carbon level decreases. Harvesting only the cob portion of the stover would reduce the negative impact of stover removal on soil organic carbon sequestration rate while still bringing the benefit of lower nitrogen-related emissions from the soil. No-tillage practices offer higher accumulation rates of soil organic carbon, lower fuel consumption, and lower nitrogen emissions from the soil than the current or conventional tillage practices. Planting winter cover crops could be a way to reduce nitrogen losses from soil and to increase soil organic carbon levels. Recommendations and perspectives  County-level modeling is more accurate in estimating the local environmental burdens associated with biomass production than national- or regional-level modeling. When possible, site-specific experimental information on soil carbon and nitrogen dynamics should be obtained to reflect the system more accurately. The allocation approach between corn grain and stover significantly affects the environmental performance of each. The preferred allocation method is the system expansion approach where incremental fuel usage, additional nutrients in the subsequent growing season, and changes in soil carbon and nitrogen dynamics due to removing corn stover are assigned to only the collected corn stover.     

Host species,and not environment,predicts variation in blood parasite prevalence,distribution, and diversity along a humidity gradient in northern South America

Environmental factors strongly influence the ecology and evolution of vector‐borne infectious diseases. However, our understanding of the influence of climatic variation on host–parasite interactions in tropical systems is rudimentary. We studied five species of birds and their haemosporidian parasites (Plasmodium and Haemoproteus) at 16 sampling sites to understand how environmental heterogeneity influences patterns of parasite prevalence, distribution, and diversity across a marked gradient in water availability in northern South America. We used molecular methods to screen for parasite infections and to identify parasite lineages. To characterize spatial heterogeneity in water availability, we used weather‐station and remotely sensed climate data. We estimated parasite prevalence while accounting for spatial autocorrelation, and used a model selection approach to determine the effect of variables related to water availability and host species on prevalence. The prevalence, distribution, and lineage diversity of haemosporidian parasites varied among localities and host species, but we found no support for the hypothesis that the prevalence and diversity of parasites increase with increasing water availability. Host species and host × climate interactions had stronger effects on infection prevalence, and parasite lineages were strongly associated with particular host species. Because climatic variables had little effect on the overall prevalence and lineage diversity of haemosporidian parasites across study sites, our results suggest that independent host–parasite dynamics may influence patterns in parasitism in environmentally heterogeneous landscapes.     

Climate change and variability impacts on grazing herds: Insights from a system dynamics approach for semi‐arid Australian rangelands

Grazing livestock are an important source of food and income for millions of people worldwide. Changes in mean climate and increasing climate variability are affecting grasslands' carrying capacity, thus threatening the livelihood of millions of people as well as the health of grassland ecosystems. Compared with cropping systems, relatively little is known about the impact of such climatic changes on grasslands and livestock productivity and the adaptation responses available to farmers. In this study, we analysed the relationship between changes in mean precipitation, precipitation variability, farming practices and grazing cattle using a system dynamics approach for a semi‐arid Australian rangeland system. We found that forage production and animal stocking rates were significantly affected by drought intensities and durations as well as by long‐term climate trends. After a drought event, herd size recovery times ranged from years to decades in the absence of proactive restocking through animal purchases. Decreases in the annual precipitation means or increases in the interannual (year‐to‐year) and intra‐annual (month‐to‐month) precipitation variability, all reduced herd sizes. The contribution of farming practices versus climate effect on herd dynamics varied depending on the herd characteristics considered. Climate contributed the most to the variance in stocking rates, followed by forage productivity levels and feeding supplementation practices (with or without urea and molasses). While intensification strategies and favourable climates increased long‐term herd sizes, they also resulted in larger reductions in animal numbers during droughts and raised total enteric methane emissions. In the face of future climate trends, the grazing sector will need to increase its adaptability. Understanding which farming strategies can be beneficial, where, and when, as well as the enabling mechanisms required to implement them, will be critical for effectively improving rangelands and the livelihoods of pastoralists worldwide.     

Metazoan parasites of African annual killifish (Nothobranchiidae): abundance,diversity, and their environmental correlates

Estimates of biodiversity and its global patterns are affected by parasite richness and specificity. Despite this, parasite communities are largely neglected in biodiversity estimates, especially in the tropics. We studied the parasites of annual killifish of the genus Nothobranchius that inhabit annually desiccating pools across the African savannah and survive the dry period as developmentally arrested embryos. Their discontinuous, non‐overlapping generations make them a unique organism in which to study natural parasite fauna. We investigated the relationship between global (climate and altitude) and local (pool size, vegetation, host density and diversity, and diversity of potential intermediate hosts) environmental factors and the community structure of killifish parasites. We examined metazoan parasites from 21 populations of four host species (Nothobranchius orthonotus, N. furzeri, N. kadleci, and N. pienaari) across a gradient of aridity in Mozambique. Seventeen parasite taxa were recorded, with trematode larval stages (metacercariae) being the most abundant taxa. The parasites recorded were both allogenic (life cycle includes non‐aquatic host; predominantly trematodes) and autogenic (cycling only in aquatic hosts; nematodes). The parasite abundance was highest in climatic regions with intermediate aridity, while parasite diversity was associated with local environmental characteristics and positively correlated with fish species diversity and the amount of aquatic vegetation. Our results suggest that parasite communities of sympatric Nothobranchius species are similar and dominated by the larval stages of generalist parasites. Therefore, Nothobranchius serve as important intermediate or paratenic hosts of parasites, with piscivorous birds and predatory fish being their most likely definitive hosts.