Exploring manipulative strategies of a trophically-transmitted parasite across its ontogeny
Time-course of antipredator behavioral changes induced by the helminth Pomphorhynchus laevis in its intermediate host Gammarus pulex: the switch in manipulation according to parasite developmental stage differs between behaviors
Recommendation: posted 13 November 2023, validated 14 November 2023
Lefevre, T. (2023) Exploring manipulative strategies of a trophically-transmitted parasite across its ontogeny . Peer Community in Zoology, 100215. 10.24072/pci.zool.100215
The intricate relationships between parasites and their hosts often involve a choreography of behavioral changes, with parasites manipulating their hosts in a way that enhances - or seemingly enhances – their transmission (Hughes et al., 2012; Moore, 2002; Poulin, 2010). Host manipulation is increasingly acknowledged as a pervasive adaptive transmission strategy employed by parasites, and as such is one of the most remarkable manifestations of the extended phenotype (Dawkins, 1982).
In this laboratory study, Rigaud et al. (2023) delved into the time course of antipredator behavioral modifications induced by the acanthocephalan Pomphorhynchus laevis in its amphipod intermediate host Gammarus pulex. This system has a good foundation of prior knowledge (Bakker et al., 2017; Fayard et al., 2020; Perrot-Minnot et al., 2023), nicely drawn upon for the present work. This parasite orchestrates a switch from predation suppression, during the noninfective phase, to predation enhancement upon maturation. Specifically, G. pulex infected with the non-infective acanthella stage of the parasite can exhibit increased refuge use and reduced activity compared to uninfected individuals (Dianne et al., 2011, 2014), leading to decreased predation by trout (Dianne et al., 2011). In contrast, upon reaching the infective cystacanth stage, the parasite can enhance the susceptibility of its host to trout predation (Dianne et al., 2011).
The present work aimed to understand the temporal sequence of these behavioral changes across the entire ontogeny of the parasite. The results confirmed the protective role of P. laevis during the acanthella stage, wherein infected amphipods exhibited heightened refuge use. This protective manipulation, however, became significant only later in the parasite's ontogeny, suggesting a delayed investment strategy, possibly influenced by the extended developmental time of P. laevis. The protective component wanes upon reaching the cystacanth stage, transitioning into an exposure strategy, aligning with theoretical predictions and previous empirical work (Dianne et al., 2011; Parker et al., 2009). The switch was behavior-specific. Unlike the protective behavior, a decline in the amphipod activity rate manifested early in the acanthella stage and persisted throughout development, suggesting potential benefits of reduced activity for the parasite across multiple stages. Furthermore, the findings challenge previous assumptions regarding the condition-dependency of manipulation, revealing that the parasite-induced behavioral changes predominantly occurred in the presence of cues signaling potential predators. Finally, while amphipods infected with acanthella stages displayed survival rates comparable to their uninfected counterparts, increased mortality was observed in those infected with cystacanth stages.
Understanding the temporal sequence of host behavioral changes is crucial for deciphering whether it is adaptive to the parasite or not. This study stands out for its meticulous examination of multiple behaviors over the entire ontogeny of the parasite highlighting the complexity and condition-dependent nature of manipulation. The protective-then-expose strategy emerges as a dynamic process, finely tuned to the developmental stages of the parasite and the ecological challenges faced by the host. The delayed emergence of protective behaviors suggests a strategic investment by the parasite, with implications for the host's survival and the parasite's transmission success. The differential impact of infection on refuge use and activity rate further emphasizes the need for a multidimensional approach in studying parasitic manipulation (Fayard et al., 2020). This complexity demands further exploration, particularly in deciphering how trophically-transmitted parasites shape the behavioral landscape of their intermediate hosts and its temporal dynamic (Herbison, 2017; Perrot-Minnot & Cézilly, 2013). As we discover the many subtleties of these parasitic manipulations, new avenues of research are unfolding, promising a deeper understanding of the ecology and evolution of host-parasite interactions.
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Dawkins, R. (1982). The extended phenotype: The long reach of the gene (Reprinted). Oxford University Press.
Dianne, L., Perrot-Minnot, M.-J., Bauer, A., Gaillard, M., Léger, E., & Rigaud, T. (2011). Protection first then facilitation: A manipulative parasite modulates the vulnerability to predation of its intermediate host according to its own developmental stage. Evolution, 65(9), 2692–2698. https://doi.org/10.1111/j.1558-5646.2011.01330.x
Dianne, L., Perrot-Minnot, M.-J., Bauer, A., Guvenatam, A., & Rigaud, T. (2014). Parasite-induced alteration of plastic response to predation threat: Increased refuge use but lower food intake in Gammarus pulex infected with the acanothocephalan Pomphorhynchus laevis. International Journal for Parasitology, 44(3–4), 211–216. https://doi.org/10.1016/j.ijpara.2013.11.001
Fayard, M., Dechaume‐Moncharmont, F., Wattier, R., & Perrot‐Minnot, M. (2020). Magnitude and direction of parasite‐induced phenotypic alterations: A meta‐analysis in acanthocephalans. Biological Reviews, 95(5), 1233–1251. https://doi.org/10.1111/brv.12606
Herbison, R. E. H. (2017). Lessons in Mind Control: Trends in Research on the Molecular Mechanisms behind Parasite-Host Behavioral Manipulation. Frontiers in Ecology and Evolution, 5, 102. https://doi.org/10.3389/fevo.2017.00102
Hughes, D. P., Brodeur, J., & Thomas, F. (2012). Host manipulation by parasites. Oxford university press.
Moore, J. (2002). Parasites and the behavior of animals. Oxford University Press.
Parker, G. A., Ball, M. A., Chubb, J. C., Hammerschmidt, K., & Milinski, M. (2009). When should a trophically transmitted parasite manipulate its host? Evolution, 63(2), 448–458. https://doi.org/10.1111/j.1558-5646.2008.00565.x
Perrot-Minnot, M.-J., & Cézilly, F. (2013). Investigating candidate neuromodulatory systems underlying parasitic manipulation: Concepts, limitations and prospects. Journal of Experimental Biology, 216(1), 134–141. https://doi.org/10.1242/jeb.074146
Perrot-Minnot, M.-J., Cozzarolo, C.-S., Amin, O., Barčák, D., Bauer, A., Filipović Marijić, V., García-Varela, M., Servando Hernández-Orts, J., Yen Le, T. T., Nachev, M., Orosová, M., Rigaud, T., Šariri, S., Wattier, R., Reyda, F., & Sures, B. (2023). Hooking the scientific community on thorny-headed worms: Interesting and exciting facts, knowledge gaps and perspectives for research directions on Acanthocephala. Parasite, 30, 23. https://doi.org/10.1051/parasite/2023026
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Rigaud, T., Balourdet, A., & Bauer, A. (2023). Time-course of antipredator behavioral changes induced by the helminth Pomphorhynchus laevis in its intermediate host Gammarus pulex: The switch in manipulation according to parasite developmental stage differs between behaviors. bioRxiv, ver. 6 peer-reviewed and recommended by Peer Community in Zoology. https://doi.org/10.1101/2023.04.25.538244
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article. The authors declared that they comply with the PCI rule of having no financial conflicts of interest in relation to the content of the article.
Evaluation round #2
DOI or URL of the preprint: https://doi.org/10.1101/2023.04.25.538244
Version of the preprint: 5
Author's Reply, 09 Nov 2023
Decision by Thierry Lefevre, posted 07 Nov 2023, validated 07 Nov 2023
Dear Thierry and co-authors,
The two reviewers and I are satisfied with the revisions you have made. Your efforts in addressing the concerns raised by the reviewers and conducting additional analyses are greatly appreciated. Before I proceed to write the recommendation, could you please address the minor additional remarks raised by Adèle, as well as the following points:
- Abstract: Please consider replacing "with or without predation threat" with "with or without predation cues" since the risk of predation was non-existent (the predator was absent but the water was scented with the predator).
- Line 152: Consider changing "caught in February in the Vouge River" to "caught in February 2012 in the Vouge River."
- Lines 166-169: The provided sentence outlines the start and end of the experiment but does not specify the frequency at which measurements for both behaviors were recorded. While this will be evident in the results section (on the x-axis in Figures 2 and 3), it would be helpful to mention the recording frequency for these two traits here or in the paragraphs describing the procedure for measuring these traits.
- Line 159 mentions "Twenty control gammarids." In lines 170-188 (description of the procedure for refuge use measurements), does this mean that ten of these control individuals were tested with scented water and ten with unscented control water? Consider adding this information.
- Line 200: Consider removing the second part of the sentence, "...and the test was not made at day 83 for technical reasons." This is already mentioned earlier that "The experiment was stopped after 83 days post-exposure." Additionally, it's essential to clarify and standardize the terminology used to describe the three categories of gammarids: (i) infected individuals vs. (ii) unexposed-control individuals vs. (iii) exposed-uninfected individuals throughout the manuscript (also refer to the comment from referee 1). In this particular sentence (line 200), there is a double confusion: the term "gammarids unexposed to parasite eggs" is not the same as the one used in line 159: "Twenty control gammarids." Furthermore, it contradicts the beginning of this paragraph, which states: "The activity of infected and uninfected gammarids was recorded the day after the refuge use measurement." At this stage in the manuscript, the "uninfected gammarids" logically refer to the "20 unexposed control gammarids" as it is not yet mentionned that some exposed individuals remained uninfected. Yet the end of this paragraph states (lines 200) that "The 20 gammarids unexposed to parasite eggs were not measured for this trait". To avoid this confusion consider replacing "uninfected gammarids" in this sentence with "exposed-uninfected individuals" to make the distinction with the unexposed-controls.
- Line 228: The sentence "The effects of water type (scented vs. control), infection status (control vs. infected), and their interaction were investigated along time" is a bit confusing given that unexposed-control and exposed-uninfected specimens were pooled together. Should this sentence, therefore, read "uninfected" instead of "control"?
Reviewed by Adèle Mennerat, 06 Nov 2023
Reviewed by anonymous reviewer 1, 21 Oct 2023
Evaluation round #1
DOI or URL of the preprint: https://doi.org/10.1101/2023.04.25.538244
Version of the preprint: 2
Author's Reply, 04 Oct 2023
Decision by Thierry Lefevre, posted 13 Jul 2023, validated 13 Jul 2023
Dear Dr. Rigaud,
You preprint has now been read and assessed by two independent peers who both point out a lot of merit and value in the work. I also enjoyed reading the manuscript and thought these experiments provide a neat novel body of work. However, both reviewers suggest a number of changes that would make this work stronger and clearer to the scientific community. These two reviews provide valuable insights and are complementary: while the anonymous reviewer provides a list of key points regarding the material & methods, and the results sections, Adèle (who signed her review) suggests a number of concrete improvements for the introduction and discussion sections.
Specifically, the anonymous reviewer questions the validity of the results because of putative problems with the experimental setup and analyses, including the temporal pseudoreplications with repeated observations on the same individuals, the lack of clear distinction between “uninfected controls” and “exposed-uninfected” individuals, and concerns regarding the ability to effectively distinguish the parasite and accurately categorize/assign individuals during the early stages of parasite development). I agree with her/him that the distinction between "exposed-uninfected" and "unexposed controls" individuals can sometimes be misleading (e.g., line 192, see also one of Adèle's comment). I suggest that the authors give further consideration to this distinction (unexposed controls vs. exposed-uninfected) throughout the text, in the statistical analyses, and in the figures (the authors may choose to present this distinction in the main figures or produce additional supplementary figures illustrating the distinction between the 3 groups: exposed-infected vs. exposed-uninfected vs. unexposed controls). Similarly, more details about the statistical analysis would be required (an R script would be great along the already available raw data on the repository).
I also found the improvement recommendations put forward by Adèle regarding the introduction and discussion sections to be highly relevant. I would therefore encourage you to revise and resubmit your preprint to PCI Zoology together with point-by-point replies to each of the reviewers’ comments. Please indicate in each reply where changes were made in the manuscript. Once your revision is received, we will contact both reviewers for their views on whether their concerns have been adequately addressed.
Finally, below are some minor comments of my own.
Yours sincerely, Thierry Lefèvre
- Line 86. Ref Abjornsson et al. 2004 is miscited here (although interesting it has nothing to do with parasites protecting their hosts), shouldn’t it be one of Diane et al. paper instead?
- Line 108: changed instead of changes (but see one of Adèle’s comment requesting a more profound rephrasing here)
- Line 109: “known to be reduced as an antipredator defense in gammarids” (REF). Consider adding a ref after “gammarids”.
- Line 113: “P” should be italicized
- Line 117 “behavioural changes”. Consider recalling the two behavioral traits namely “refuge use and activity rate” in parenthesis
- Line 121: “are these two different anti-predatory…”. I assume that the word "these" refers to "activity rate and shelter use", but "activity rate" has not yet been mentioned in this paragraph so it's not clear what "these" refers to here.
- Line 134 The use of the word "also" here implies that the parasite was collected from the same river as the gammarids. This would indeed be relevant, as it would indicate the use in the laboratory of a sympatric combination that has coevolved in the field. However, line 130 states that the gammarids were collected from a branch of the Suzon, while line 134 states that the parasites were collected from the Vouge. Is the Vouge the name of the branch of the Suzon mentioned in line 130?
- Line 148: “every week”. Consider rephrasing to make it clear how many times this trait was measured e.g. “…measured once a week from day 21 to day 83”.
- Line 164: You meant day 83 instead of 84? This sentence is confusing (see also one of Adèle’s comment)
- Line 186: This is a bit confusing as you wrote at lines 163 that the activity rate of the 20 unexposed gammarids were not measured?
- Line 211: “175 individuals”. Shouldn’t this read 180 (see line 138).
- Line 227: “under scented water”. Could it possibly be “under control water” instead? Please double check and consider rewording this sentence, I found this sentence confusing.
- Line 237 the variable “number of parasites” is a discrete numerical (and not continuous) factor.
- Caption of figure 2: specify what the vertical black line represent on the figure (acanthella à cystacanth transition?)
- Line 265: “but here a dichotomy must be made” unclear. Figure 2 also makes the distinction between scented and control water.
- Line 269: I assume you meant -0.11 and -0.4 (instead of 0.11 and 0.4)?
- Line 272: becoming negative should read “becoming positive”, right?
- Line 290: “were not” instead of “were no”
- Line 292: discrete numerical variable
- Line 315: “general trend to decrease” instead of “increase”?
- Line 330: “involved in predation avoidance”. Please cite a ref here.
- Line 335-336: consider deleting “as seen using effect sizes” (Figure 2 also shows this).
- Line 400: “was also strengthen by infection”. Please rephrase as the results indicate the contrary i.e. infected individuals are less active.