Host Density and Competency Determine the Effects of Host Diversity on Trematode Parasite Infection

<div><p>Variation in host species composition can dramatically alter parasite transmission in natural communities. Whether diverse host communities dilute or amplify parasite transmission is thought to depend critically on species traits, particularly on how hosts affect each other’s densities, and their relative competency as hosts. Here we studied a community of potential hosts and/or decoys (i.e. non-competent hosts) for two trematode parasite species, <i>Echinostoma trivolvis</i> and <i>Ribeiroia ondatrae</i>, which commonly infect wildlife across North America. We manipulated the density of a focal host (green frog tadpoles, <i>Rana clamitans</i>), in concert with manipulating the diversity of alternative species, to simulate communities where alternative species either (1) replace the focal host species so that the total number of individuals remains constant (substitution) or (2) add to total host density (addition). For <i>E. trivolvis</i>, we found that total parasite transmission remained roughly equal (or perhaps decreased slightly) when alternative species replaced focal host individuals, but parasite transmission was higher when alternative species were added to a community without replacing focal host individuals. Given the alternative species were roughly equal in competency, these results are consistent with current theory. Remarkably, both total tadpole and <i>per-capita</i> tadpole infection intensity by <i>E. trivolvis</i> increased with increasing intraspecific host density. For <i>R. ondatrae</i>, alternative species did not function as effective decoys or hosts for parasite infective stages, and the diversity and density treatments did not produce clear changes in parasite transmission, although high tank to tank variation in <i>R. ondatrae</i> infection could have obscured patterns.</p></div

Counts of <i>E. trivolvis</i> metacerariae versus tadpole mass (log scaled), for the six tadpole density and host diversity treatments.

<p>Dots are observed infection intensities in individual tadpoles, thick lines are the predicted (from NB GLMM model) infection intensity for an animal of a given mass in that treatment, and thin lines represent 95% Bayesian credible intervals. Larger animals were more likely to be infected, but the rate of increased infection with size depended on treatment. Note that per-capita ETa infection increased with <i>Rana</i> density (R16 vs. R24 vs. R48), but was not affected by the addition of alternative hosts (RHP vs. R16, RH & RP vs. R24).</p

<i>E. trivolvis</i> infection by host species, and in total, for each treatment. Means plus one standard error are reported.

<p>Shades of purple represent the individual host taxa, while the wider gray bars represent the total of multi-species communities. Total infection increased with <i>Rana</i> density (R16 vs. R24 vs. R48). There was more total infection in diverse communities when host densities were additive (R16 vs. RHP or R24 vs. RH/RP), but equal infection in diverse communities when host densities were substitutive (RHP/RH/RP vs. R48).</p

<i>R. ondatrae</i> infection in each of the six tadpole density and host/decoy treatments.

<p>Each point represents the total number of metacercariae among all the animals in a single tank. The high tank to tank variability within each treatment made detecting any potential treatment differences difficult.</p

<i>Bd</i> Prevalence and infection intensity among three lowland species of frogs.

<p><b>CI 95%  = </b> Confidence intervals based on 95% confidence.</p><p><b>a = </b>Infection prevalence = % of infected individuals.</p><p><b>b = </b>Average number of zoospore equivalents on infected individuals according to JEL423 standards.</p

Map of Panamá showing the sites where <i>Bd</i> has been detected in previous studies and this study.

<p>The year next to each black circle shows the date when <i>Bd</i> was <b>first</b> detected on each site. <b>a</b> = Fortuna <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Berger2" target="_blank">[8]</a>; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Lips4" target="_blank">[50]</a>. <b>b</b>, <b>c</b>, <b>d</b>, <b>e</b>, <b>f</b>, <b>g</b> and <b>h</b> = Parque Nacional Santa Fe, Altos de Piedra, Santiago marsh, Road pools, Río Grande watershed, Río Colorado watershed at bridge, Río Colorado watershed respectively <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Brem1" target="_blank">[19]</a>. <b>i</b> = El Copé <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Lips1" target="_blank">[6]</a>. <b>j</b>, <b>k</b>, <b>l</b> and <b>m</b> = La Rica, Palmarazo, Cuatro Callitas and Cerro Trinidad respectively <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Kilburn1" target="_blank">[20]</a>. <b>n</b> = El Valle <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Gagliardo1" target="_blank">[51]</a>. <b>o</b> and <b>p</b>  =  Parque Nacional Altos de Campana and Parque Nacional Soberanía <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Woodhams1" target="_blank">[13]</a>. <b>q</b> = Tortí <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0095484#pone.0095484-Kng1" target="_blank">[18]</a>.</p

Athlétic-tribune sportive : hebdomadaire illustré / [directeurs Roger Roujean, Pierre Pradeu]

26 octobre 19331933/10/26 (A15,N708)-1933/10/26.Appartient à l’ensemble documentaire : Aquit

Mean <i>Bd</i> prevalence and infection intensity (zoospore genome equivalents) of three species of frogs across five sites in Panamá. NA

<p> =  No data available. Bars correspond to 95% confidence intervals. <b>A</b>, <b>C</b> and <b>E</b> show pathogen prevalence (% of infected individuals). <b>A)</b><i>A. callidryas</i> across five sites <b>C)</b><i>D. ebraccatus</i> across five sites. <b>E)</b><i>C. fitzingeri</i> across three sites. <b>B</b>, <b>D</b> and <b>F</b> show Intensity of <i>Bd</i> infection based on the number of zoospore genome equivalents according to the reference strain JEL423. <b>B)</b><i>A. callidryas</i> across five sites. <b>D)</b><i>D. ebraccatus</i> across five sites. <b>F)</b><i>C. fitzingeri</i> across three sites. Note that the scale of the Y axis begins as arithmetic and changes to logarithmic in order to present the data from the three sites on the same figure.</p

Effects of Bd exposure (white bars = No exposure to Bd; grey bars = Exposure to Bd) and bacterial treatment (normal, antibiotics, and augmented with <i>J</i>. <i>lividum</i>) on OTU richness (a), phylogenetic diversity (b), and relative abundance of the probiotic <i>J</i>. <i>lividum</i> (c) on bullfrog skin one week following exposure to Bd (day 7).

<p>Error bars represent standard error. * represent significant differences among treatments.</p

Conceptual model representing potential responses and interpretations of microbial community structure and function in the presence of a pathogen.

<p>Conceptual model representing potential responses and interpretations of microbial community structure and function in the presence of a pathogen.</p