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

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.

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

10.22541/au.163277469.97557253/v1 ◽

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.

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Biodiversity inhibits parasites: Broad evidence for the dilution effect

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1506279112 ◽

2015 ◽

Vol 112 (28) ◽

pp. 8667-8671 ◽

Cited By ~ 258

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.

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Negative density-dependent parasitism in a group-living carnivore

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.2655 ◽

2020 ◽

Vol 287 (1941) ◽

pp. 20202655

Author(s):

Gregory F. Albery ◽

Chris Newman ◽

Julius Bright Ross ◽

David W. MacDonald ◽

Shweta Bansal ◽

...

Keyword(s):

Local Population ◽

Group Living ◽

Host Density ◽

Meles Meles ◽

Population Variation ◽

Network Analyses ◽

Long Term Study ◽

Negative Density Dependence ◽

Dilution Effects

Animals living at high population densities commonly experience greater exposure to disease, leading to increased parasite burdens. However, social animals can benefit immunologically and hygienically from cooperation, and individuals may alter their socio-spatial behaviour in response to infection, both of which could counteract density-related increases in exposure. Consequently, the costs and benefits of sociality for disease are often uncertain. Here, we use a long-term study of a wild European badger population ( Meles meles ) to investigate how within-population variation in host density determines infection with multiple parasites. Four out of five parasite taxa exhibited consistent spatial hotspots of infection, which peaked among badgers living in areas of low local population density. Combined movement, survival, spatial and social network analyses revealed that parasite avoidance was the likely cause of this negative density dependence, with possible roles for localized mortality, encounter-dilution effects, and micronutrient-enhanced immunity. These findings demonstrate that animals can organize their societies in space to minimize parasite infection, with important implications for badger behavioural ecology and for the control of badger-associated diseases.

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Evolution in interacting species alters predator life-history traits, behaviour and morphology in experimental microbial communities

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2020.0652 ◽

2020 ◽

Vol 287 (1928) ◽

pp. 20200652

Author(s):

Johannes Cairns ◽

Felix Moerman ◽

Emanuel A. Fronhofer ◽

Florian Altermatt ◽

Teppo Hiltunen

Keyword(s):

Life History ◽

Prey Species ◽

Rapid Evolution ◽

Prey Type ◽

Automated Image Analysis ◽

Foraging Efficiency ◽

Predator Prey ◽

Evolving Systems ◽

Interacting Species ◽

Evolutionary Response

Predator–prey interactions heavily influence the dynamics of many ecosystems. An increasing body of evidence suggests that rapid evolution and coevolution can alter these interactions, with important ecological implications, by acting on traits determining fitness, including reproduction, anti-predatory defence and foraging efficiency. However, most studies to date have focused only on evolution in the prey species, and the predator traits in (co)evolving systems remain poorly understood. Here, we investigated changes in predator traits after approximately 600 generations in a predator–prey (ciliate–bacteria) evolutionary experiment. Predators independently evolved on seven different prey species, allowing generalization of the predator's evolutionary response. We used highly resolved automated image analysis to quantify changes in predator life history, morphology and behaviour. Consistent with previous studies, we found that prey evolution impaired growth of the predator, although the effect depended on the prey species. By contrast, predator evolution did not cause a clear increase in predator growth when feeding on ancestral prey. However, predator evolution affected morphology and behaviour, increasing size, speed and directionality of movement, which have all been linked to higher prey search efficiency. These results show that in (co)evolving systems, predator adaptation can occur in traits relevant to foraging efficiency without translating into an increased ability of the predator to grow on the ancestral prey type.

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Weak-lensing clusters from HSC survey first-year data: Mitigating the dilution effect of foreground and cluster-member galaxies

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa068 ◽

2020 ◽

Vol 72 (5) ◽

Cited By ~ 1

Author(s):

Takashi Hamana ◽

Masato Shirasaki ◽

Yen-Ting Lin

Keyword(s):

Dilution Effect ◽

Weak Lensing ◽

First Year ◽

Cluster Member ◽

The Public ◽

Photometric Redshift ◽

Source Sample ◽

Strategic Program ◽

Dilution Effects ◽

Cross Match

Abstract We present a weak-lensing cluster search using Hyper Suprime-Cam Subaru Strategic Program (HSC survey) first-year data. We pay special attention to the dilution effect of cluster-member and foreground galaxies on weak-lensing signals from clusters of galaxies; we adopt the globally normalized weak-lensing estimator which is least affected by cluster-member galaxies, and we select source galaxies by using photometric redshift information to mitigate the effect of foreground galaxies. We produce six samples of source galaxies with different low-z galaxy cuts, construct weak-lensing mass maps for each source sample, and search for high peaks in the mass maps that cover an effective survey area of ∼120 deg2. We combine six catalogs of high peaks into a sample of cluster candidates which contains 124 high peaks with signal-to-noise ratios greater than five. We cross-match the peak sample with the public optical cluster catalog constructed from the same HSC survey data to identify cluster counterparts of the peaks. We find that 107 out of 124 peaks have matched clusters within 5′ of peak positions. Among them, we define a subsample of 64 secure clusters that we use to examine dilution effects on our weak-lensing cluster search. We find that source samples with low-z galaxy cuts mitigate the dilution effect on weak-lensing signals of high-z clusters ($z \gtrsim 0.3$), and thus combining multiple peak catalogs from different source samples improves the efficiency of weak-lensing cluster searches.

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Dynamic Dilution Effects in Polymeric Networks

e-Polymers ◽

10.1515/epoly.2006.6.1.555 ◽

2006 ◽

Vol 6 (1) ◽

Cited By ~ 2

Author(s):

Anne Ladegaard Larsen ◽

Peter Sommer-Larsen ◽

Ole Hassager

Keyword(s):

Low Frequency ◽

Dilution Effect ◽

Relaxation Processes ◽

Single Chain ◽

Relaxation Spectra ◽

Polymeric Networks ◽

Dilution Effects

AbstractThe relaxation processes occurring in slightly and well-entangled polydimetylsiloxane (PDMS) networks are investigated. Swelling experiments are performed in order to determine the sol fractions. The low-frequency linear rheology of the two types of networks reveal two significant relaxation processes, namely the reptation of linear species within the network and the arm withdrawal process of star arms in the sol fraction and of dangling single-chain ends attached to the network. The relaxation spectra are influenced by the stoichiometry to a large extent due to dynamic dilution effects caused by the change in the amount of dangling arms and solubles with stoichiometry. The star arm relaxation is suppressed by washing out the sol fraction which is seen as a clear example of the dynamic dilution effect arising from the small amount of non-reactive PDMS.

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Inventory of organisms interfering with transmission of a marine trematode

Journal of the Marine Biological Association of the United Kingdom ◽

10.1017/s0025315414000034 ◽

2014 ◽

Vol 94 (4) ◽

pp. 697-702 ◽

Cited By ~ 23

Author(s):

Jennifer E. Welsh ◽

Jaap van der Meer ◽

Corina P.D. Brussaard ◽

David W. Thieltges

Keyword(s):

Crassostrea Gigas ◽

Wadden Sea ◽

Dilution Effect ◽

Crangon Crangon ◽

Trematode Parasite ◽

Free Living ◽

Marine Systems ◽

Time Period ◽

Idotea Balthica ◽

Dilution Effects

It has increasingly been recognized that organisms can interfere with parasitic free-living stages, preventing them from infecting their specified host and thus reducing infection levels. This common phenomenon in freshwater and terrestrial systems has been termed the ‘dilution effect’ and, so far, is poorly studied in marine systems. Ten common intertidal organisms found in the Dutch Wadden Sea (North Sea) were tested to establish their effects on the free-living cercarial stages of the trematode parasite Himasthla elongata. Most species tested resulted in a significant reduction in cercariae over a 3 hr time period. The amphipod Gammarus marinus removed 100% of the cercariae, while other effective diluters were Crangon crangon (93%), Sargassum muticum (87%), Semibalanus balanoides (71%), Crassostrea gigas (67%), Hemigrapsus takanoi (>54%), Crassostrea gigas shells (44%) and Idotea balthica (24%). In contrast, mixed shells (Cerastoderma edule, Mytilus edulis, Ensis americanus and Littorina littorea) and Fucus versiculosus had no significant effect. These results suggest that dilution effects are widespread in the trematode of H. elongata, with potentially strong effects on its population dynamics.

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An Herbicide-Susceptible Rigid Ryegrass (Lolium rigidum) Population Made Even More Susceptible

Weed Science ◽

10.1614/ws-d-11-00076.1 ◽

2012 ◽

Vol 60 (1) ◽

pp. 101-105 ◽

Cited By ~ 10

Author(s):

Sudheesh Manalil ◽

Roberto Busi ◽

Michael Renton ◽

Stephen B. Powles

Keyword(s):

Genetic Variation ◽

Phenotypic Variation ◽

Recurrent Selection ◽

Wild Population ◽

Rapid Evolution ◽

Differential Susceptibility ◽

Variable Cross ◽

Lolium Rigidum ◽

Rigid Ryegrass ◽

Low Rate

A wild population of a plant species, especially a cross-pollinated species, can display considerable genetic variation. Genetic variability is evident in differential susceptibility to an herbicide because the population can show continuous phenotypic variation. Recent, recurrent selection studies have revealed that phenotypic variation in response to low herbicide rates is heritable and can result in rapid evolution of herbicide resistance in genetically variable cross-pollinated rigid ryegrass. In this study, the heritable genetic variation in an herbicide-susceptible rigid ryegrass population was exploited to shift the population toward greater herbicide susceptibility by recurrent selection. To enhance herbicide susceptibility, herbicide-susceptible rigid ryegrass plants were divided into two identical clones, and one series of cloned plants was treated with a low rate of herbicide (diclofop). The nontreated clones of individuals that did not survive the herbicide treatment were selected and bulk-crossed to obtain the susceptible progeny. After two cycles of selection, the overall susceptibility to diclofop was doubled. The results indicate that minor genes for resistance are present in an herbicide-susceptible rigid ryegrass population, and their exclusion can increase susceptibility to diclofop.

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Cascading effects of a highly specialized beech-aphid-fungus interaction on forest regeneration

10.7287/peerj.preprints.340v1 ◽

2014 ◽

Author(s):

Susan Susan Cook-Patton ◽

Lauren Maynard ◽

Nathan Susan Lemoine ◽

Jessica Susan Shue ◽

John D Parker

Keyword(s):

Forest Regeneration ◽

Host Density ◽

Common Garden ◽

Fagus Grandifolia ◽

Common Garden Experiment ◽

American Beech ◽

Cascading Effects ◽

Specialist Herbivores ◽

Negative Impacts ◽

Survival Of Seedlings

Specialist herbivores are often thought to benefit the larger plant community, because they prevent their host species from becoming competitively dominant. In contrast, specialist enemies are not generally expected to have negative impacts on non-hosts. However, we describe a cascade of indirect interactions whereby a specialist sooty mold (Scorias spongiosa) colonizes the honeydew from a specialist beech aphid (Grylloprociphilus imbricator), ultimately decreasing the survival of seedlings beneath American beech trees (Fagus grandifolia). A common garden experiment indicated that this mortality resulted from moldy honeydew impairing leaf function rather than from chemical or microbial changes to the soil. In addition, aphids consistently colonized the same beech trees regardless of host density, suggesting that seedling-depauperate islands may form beneath these trees. Thus this highly specialized three-way beech-aphid-fungus interaction has the potential to impact local forest regeneration via a cascade of indirect effects.

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Contemporary and historical selection in Tasmanian devils ( Sarcophilus harrisii ) support novel, polygenic response to transmissible cancer

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2021.0577 ◽

2021 ◽

Vol 288 (1951) ◽

pp. 20210577

Author(s):

Amanda R. Stahlke ◽

Brendan Epstein ◽

Soraia Barbosa ◽

Mark J. Margres ◽

Austin H. Patton ◽

...

Keyword(s):

Candidate Genes ◽

Rapid Evolution ◽

Gene Sets ◽

Devil Facial Tumour Disease ◽

Evolutionary Response ◽

Recent Emergence ◽

Transmissible Cancer ◽

Or Gene ◽

Genomic Regions ◽

Sarcophilus Harrisii

Tasmanian devils ( Sarcophilus harrisii ) are evolving in response to a unique transmissible cancer, devil facial tumour disease (DFTD), first described in 1996. Persistence of wild populations and the recent emergence of a second independently evolved transmissible cancer suggest that transmissible cancers may be a recurrent feature in devils. Here, we compared signatures of selection across temporal scales to determine whether genes or gene pathways under contemporary selection (six to eight generations) have also been subject to historical selection (65–85 Myr). First, we used targeted sequencing, RAD-capture, in approximately 2500 devils in six populations to identify genomic regions subject to rapid evolution. We documented genome-wide contemporary evolution, including 186 candidate genes related to cell cycling and immune response. Then we used a molecular evolution approach to identify historical positive selection in devils compared to other marsupials and found evidence of selection in 1773 genes. However, we found limited overlap across time scales, with only 16 shared candidate genes, and no overlap in enriched functional gene sets. Our results are consistent with a novel, multi-locus evolutionary response of devils to DFTD. Our results can inform conservation by identifying high priority targets for genetic monitoring and guiding maintenance of adaptive potential in managed populations.

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