scholarly journals Biodiversity inhibits parasites: Broad evidence for the dilution effect

2015 ◽  
Vol 112 (28) ◽  
pp. 8667-8671 ◽  
Author(s):  
David J. Civitello ◽  
Jeremy Cohen ◽  
Hiba Fatima ◽  
Neal T. Halstead ◽  
Josue Liriano ◽  
...  
Keyword(s):  
Disease Risk ◽  
Meta Analysis ◽  
Host Density ◽  
Dilution Effect ◽  
Wildlife Diseases ◽  
Parasite Abundance ◽  
Effect Hypothesis ◽  
Zoonotic Parasites ◽  
Dilution Effects ◽  
Plant Herbivore

Infectious diseases of humans, wildlife, and domesticated species are increasing worldwide, driving the need to understand the mechanisms that shape outbreaks. Simultaneously, human activities are drastically reducing biodiversity. These concurrent patterns have prompted repeated suggestions that biodiversity and disease are linked. For example, the dilution effect hypothesis posits that these patterns are causally related; diverse host communities inhibit the spread of parasites via several mechanisms, such as by regulating populations of susceptible hosts or interfering with parasite transmission. However, the generality of the dilution effect hypothesis remains controversial, especially for zoonotic diseases of humans. Here we provide broad evidence that host diversity inhibits parasite abundance using a meta-analysis of 202 effect sizes on 61 parasite species. The magnitude of these effects was independent of host density, study design, and type and specialization of parasites, indicating that dilution was robust across all ecological contexts examined. However, the magnitude of dilution was more closely related to the frequency, rather than density, of focal host species. Importantly, observational studies overwhelmingly documented dilution effects, and there was also significant evidence for dilution effects of zoonotic parasites of humans. Thus, dilution effects occur commonly in nature, and they may modulate human disease risk. A second analysis identified similar effects of diversity in plant–herbivore systems. Thus, although there can be exceptions, our results indicate that biodiversity generally decreases parasitism and herbivory. Consequently, anthropogenic declines in biodiversity could increase human and wildlife diseases and decrease crop and forest production.

scholarly journals The dilution effect in a freshwater mutualism: impacts of introduced host species on native symbionts

2021 ◽  
Author(s):  
Robert Creed ◽  
Gretchen L. Bailey ◽  
James Skelton ◽  
Bryan L. Brown
Keyword(s):  
Host Species ◽  
Host Density ◽  
Dilution Effect ◽  
Negative Effects ◽  
Parasite Abundance ◽  
Host Diversity ◽  
Negative Effect ◽  
Dilution Effects ◽  
Native Crayfish ◽  
Native Host

The dilution effect was originally proposed to describe the negative effect of increased host diversity on parasite abundance; with greater host diversity, parasite levels per host are predicted to be lower due to a higher probability of dispersing parasites encountering non-competent hosts. Dilution effects could also occur in many mutualisms if dispersing symbionts encounter hosts that vary in their competency. The introduction of non-native hosts can change community competency of a local group of host species. Crayfish introductions are occurring world-wide and these introductions are likely disrupting native crayfish-symbiont systems. Branchiobdellidan symbionts declined on native Cambarus crayfish occurring in the presence and absence of non-native Faxonius crayfish in the New River, USA. We performed an experiment investigating the effect of host density (1 vs 2 native hosts) and host diversity (1 native host and 1 introduced host) on branchiobdellidan abundance. The introduced F. cristavarius is a non-competent host for these worms. Six C. ingens were stocked on a C. chasmodactylus in each treatment and worm numbers were followed over 34 days. Worm numbers decreased over time on C. chasmodactylus alone and in the treatment in which a C. chasmodactylus was paired with an F. cristavarius. Worm numbers remained highest in the 2 C. chasmodactylus treatment . There was no significant effect of host diversity on worm reproduction. Crayfish invasions may have negative effects on mutualistic symbionts depending on the competence of introduced hosts. Loss of native symbionts is one of the potential hidden, negative effects of invasions on native freshwater diversity.

scholarly journals Rapid evolution rescues hosts from competition and disease but—despite a dilution effect—increases the density of infected hosts

2017 ◽  
Vol 284 (1868) ◽  
pp. 20171970 ◽  
Author(s):  
Alexander T. Strauss ◽  
Jessica L. Hite ◽  
Marta S. Shocket ◽  
Carla E. Cáceres ◽  
Meghan A. Duffy ◽  
...  
Keyword(s):  
Phenotypic Variation ◽  
Competitive Ability ◽  
Potential Problem ◽  
Rapid Evolution ◽  
Host Density ◽  
Dilution Effect ◽  
Shared Resources ◽  
Evolutionary Response ◽  
Negative Impacts ◽  
Dilution Effects

Virulent parasites can depress the densities of their hosts. Taxa that reduce disease via dilution effects might alleviate this burden. However, ‘diluter’ taxa can also depress host densities through competition for shared resources. The combination of disease and interspecific competition could even drive hosts extinct. Then again, genetically variable host populations can evolve in response to both competitors and parasites. Can rapid evolution rescue host density from the harm caused by these ecological enemies? How might such evolution influence dilution effects or the size of epidemics? In a mesocosm experiment with planktonic hosts, we illustrate the joint harm of competition and disease: hosts with constrained evolutionary ability (limited phenotypic variation) suffered greatly from both. However, populations starting with broader phenotypic variation evolved stronger competitive ability during epidemics. In turn, enhanced competitive ability—driven especially by parasites—rescued host densities from the negative impacts of competition, disease, and especially their combination. Interspecific competitors reduced disease (supporting dilution effects) even when hosts rapidly evolved. However, this evolutionary response also elicited a potential problem. Populations that evolved enhanced competitive ability and maintained robust total densities also supported higher densities of infections. Thus, rapid evolution rescued host densities but also unleashed larger epidemics.

The diversity–disease relationship: evidence for and criticisms of the dilution effect

Parasitology ◽  
2016 ◽  
Vol 143 (9) ◽  
pp. 1075-1086 ◽  
Author(s):  
Z. Y. X. HUANG ◽  
F. VAN LANGEVELDE ◽  
A. ESTRADA-PEÑA ◽  
G. SUZÁN ◽  
W. F. DE BOER
Keyword(s):  
Species Diversity ◽  
Host Species ◽  
Disease Risk ◽  
Current Knowledge ◽  
Risk Measures ◽  
Extinction Risk ◽  
Meta Analysis ◽  
Negative Relationship ◽  
Dilution Effect ◽  
Landscape Fragmentation

SUMMARYThe dilution effect, that high host species diversity can reduce disease risk, has attracted much attention in the context of global biodiversity decline and increasing disease emergence. Recent studies have criticized the generality of the dilution effect and argued that it only occurs under certain circumstances. Nevertheless, evidence for the existence of a dilution effect was reported in about 80% of the studies that addressed the diversity–disease relationship, and a recent meta-analysis found that the dilution effect is widespread. We here review supporting and critical studies, point out the causes underlying the current disputes. The dilution is expected to be strong when the competent host species tend to remain when species diversity declines, characterized as a negative relationship between species’ reservoir competence and local extinction risk. We here conclude that most studies support a negative competence–extinction relationship. We then synthesize the current knowledge on how the diversity–disease relationship can be modified by particular species in community, by the scales of analyses, and by the disease risk measures. We also highlight the complex role of habitat fragmentation in the diversity–disease relationship from epidemiological, evolutionary and ecological perspectives, and construct a synthetic framework integrating these three perspectives. We suggest that future studies should test the diversity–disease relationship across different scales and consider the multiple effects of landscape fragmentation.

scholarly journals A field test of the dilution effect hypothesis in four avian multi-host pathogens

2021 ◽  
Vol 17 (6) ◽  
pp. e1009637
Author(s):  
Martina Ferraguti ◽  
Josué Martínez-de la Puente ◽  
Miguel Ángel Jiménez–Clavero ◽  
Francisco Llorente ◽  
David Roiz ◽  
...  
Keyword(s):  
Species Richness ◽  
Species Diversity ◽  
Passer Domesticus ◽  
Host Density ◽  
Dilution Effect ◽  
Pathogen Transmission ◽  
Opposite Pattern ◽  
Vector Borne ◽  
Effect Hypothesis ◽  
Community Variables

The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens–three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)–and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.

Mutual dilution of infection by an introduced parasite in native and invasive stream fishes across Hawaii

Parasitology ◽  
2016 ◽  
Vol 143 (12) ◽  
pp. 1605-1614 ◽  
Author(s):  
RODERICK B. GAGNE ◽  
DAVID C. HEINS ◽  
PETER B. MCINTYRE ◽  
JAMES F. GILLIAM ◽  
MICHAEL J. BLUM
Keyword(s):  
Water Quality ◽  
Native Species ◽  
Host Density ◽  
Dilution Effect ◽  
Urban Land Use ◽  
Parasite Abundance ◽  
Species Of Conservation Concern ◽  
Awaous Stamineus ◽  
Conservation Concern ◽  
Camallanus Cotti

SUMMARYThe presence of introduced hosts can increase or decrease infections of co-introduced parasites in native species of conservation concern. In this study, we compared parasite abundance, intensity, and prevalence between nativeAwaous stamineusand introduced poeciliid fishes by a co-introduced nematode parasite (Camallanus cotti) in 42 watersheds across the Hawaiian Islands. We found that parasite abundance, intensity and prevalence were greater in native than introduced hosts. Parasite abundance, intensity and prevalence withinA. stamineusvaried between years, which largely reflected a transient spike in infection in three remote watersheds on Molokai. At each site we measured host factors (length, density of native host, density of introduced host) and environmental factors (per cent agricultural and urban land use, water chemistry, watershed area and precipitation) hypothesized to influenceC. cottiabundance, intensity and prevalence. Factors associated with parasitism differed between native and introduced hosts. Notably, parasitism of native hosts was higher in streams with lower water quality, whereas parasitism of introduced hosts was lower in streams with lower water quality. We also found that parasite burdens were lower in both native and introduced hosts when coincident. Evidence of a mutual dilution effect indicates that introduced hosts can ameliorate parasitism of native fishes by co-introduced parasites, which raises questions about the value of remediation actions, such as the removal of introduced hosts, in stemming the rise of infectious disease in species of conservation concern.

The burden of cardiovascular disease risk factors in the Middle East: A systematic review and meta-analysis focusing on primary prevention

2020 ◽  
Vol 18 ◽  
Author(s):  
Akshaya Srikanth Bhagavathula ◽  
Abdullah Shehab ◽  
Anhar Ullah ◽  
Jamal Rahmani
Keyword(s):  
Risk Factors ◽  
Systematic Review ◽  
Cardiovascular Disease ◽  
Family History ◽  
Primary Prevention ◽  
Middle East ◽  
Disease Risk ◽  
Meta Analysis ◽  
Middle Eastern ◽  
History Of

Background: The increasing incidence of cardiovascular disease (CVD) threatens the Middle Eastern population. Several epidemiological studies have assessed CVD and its risk factors in terms of the primary prevention of CVD in the Middle East. Therefore, summarizing the information from these studies is essential. Aim: We conducted a systematic review to assess the prevalence of CVD and its major risk factors among Middle Eastern adults based on the literature published between January 1, 2012 and December 31, 2018 and carried out a meta-analysis. Methods: We searched electronic databases such as PubMed/Medline, ScienceDirect, Embase and Google Scholar to identify literature published from January 1, 2012 to December 31, 2018. All the original articles that investigated the prevalence of CVD and reported at least one of the following factors were included: hypertension, diabetes, dyslipidaemia, smoking and family history of CVD. To summarize CVD prevalence, we performed a random-effects meta-analysis. Results: A total of 41 potentially relevant articles were included, and 32 were included in the meta-analysis (n=191,979). The overall prevalence of CVD was 10.1% (95% confidence interval (CI): 7.1-14.3%, p<0.001) in the Middle East. A high prevalence of CVD risk factors, such as dyslipidaemia (43.3%; 95% CI: 21.5-68%), hypertension (26.2%; 95% CI: 19.6-34%) and diabetes (16%; 95% CI: 9.9-24.8%), was observed. The prevalence rates of other risk factors, such as smoking (12.4%; 95% CI: 7.7-19.4%) and family history of CVD (18.7%; 95% CI: 15.4-22.5%), were also high. Conclusion: The prevalence of CVD is high (10.1%) in the Middle East. The burden of dyslipidaemia (43.3%) in this region is twice as high as that of hypertension (26.2%) and diabetes mellitus (16%). Multifaceted interventions are urgently needed for the primary prevention of CVD in this region.

scholarly journals Disentangling transcriptional responses in plant defense against arthropod herbivores

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Alejandro Garcia ◽  
M. Estrella Santamaria ◽  
Isabel Diaz ◽  
Manuel Martinez
Keyword(s):  
Regulatory Networks ◽  
Pieris Rapae ◽  
Meta Analysis ◽  
Plant Response ◽  
Plant Responses ◽  
Transcriptional Responses ◽  
Crop Species ◽  
Physiological Processes ◽  
Meta Analyses ◽  
Plant Herbivore

AbstractThe success in the response of a plant to a pest depends on the regulatory networks that connect plant perception and plant response. Meta-analyses of transcriptomic responses are valuable tools to discover novel mechanisms in the plant/herbivore interplay. Considering the quantity and quality of available transcriptomic analyses, Arabidopsis thaliana was selected to test the ability of comprehensive meta-analyses to disentangle plant responses. The analysis of the transcriptomic data showed a general induction of biological processes commonly associated with the response to herbivory, like jasmonate signaling or glucosinolate biosynthesis. However, an uneven induction of many genes belonging to these biological categories was found, which was likely associated with the particularities of each specific Arabidopsis-herbivore interaction. A thorough analysis of the responses to the lepidopteran Pieris rapae and the spider mite Tetranychus urticae highlighted specificities in the perception and signaling pathways associated with the expression of receptors and transcription factors. This information was translated to a variable alteration of secondary metabolic pathways. In conclusion, transcriptomic meta-analysis has been revealed as a potent way to sort out relevant physiological processes in the plant response to herbivores. Translation of these transcriptomic-based analyses to crop species will permit a more appropriate design of biotechnological programs.

Sign in / Sign up

Export Citation Format

Share Document