Alexandre Bauer

University of Burgundy, Dijon, Bourgogne, France

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Publications (13)34.01 Total impact

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    ABSTRACT: Larvae of many trophically-transmitted parasites alter the behaviour of their intermediate host in ways that increase their probability of transmission to the next host in their life cycle. Before reaching a stage that is infective to the next host, parasite larvae may develop through several larval stages in the intermediate host that are not infective to the definitive host. Early predation at these stages results in parasite death, and it has recently been shown that non-infective larvae of some helminths decrease such risk by enhancing the anti-predator defences of the host, including decreased activity and increased sheltering. However, these behavioural changes may divert infected hosts from an optimal balance between survival and foraging (either seeking food or a mate). In this study, this hypothesis was tested using the intermediate host of the acanthocephalan parasite Pomphorhynchus laevis, the freshwater amphipod Gammarus pulex. We compared activity, refuge use, food foraging and food intake of hosts experimentally infected with the non-infective stage (acanthella), with that of uninfected gammarids. Behavioural assays were conducted in four situations varying in predation risk and in food accessibility. Acanthella-infected amphipods showed an increase in refuge use and a general reduction in activity and food intake. There was no effect of parasite intensity on these traits. Uninfected individuals showed plastic responses to water-borne cues from fish by adjusting refuge use, activity and food intake. They also foraged more when the food was placed outside the refuge. At the intra-individual level, refuge use and food intake were positively correlated in infected gammarids only. Overall, our findings suggest that uninfected gammarids exhibit risk-sensitive behaviour including increased food intake under predation risk, whereas gammarids infected with the non-infective larvae of P. laevis exhibit a lower motivation to feed, irrespective of predation risk and food accessibility.
    International journal for parasitology 11/2013; · 3.39 Impact Factor
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    ABSTRACT: Many trophically-transmitted parasites with complex life cycles manipulate their intermediate host behaviour in ways facilitating their transmission to final host by predation. This facilitation generally results from lowering host anti-predatory defences when the parasite is infective to the final host. Since non-infective parasite stages cannot successfully establish in the next host, a recent theoretical model showed that they should enhance their own survival (and thus increase their future transmission probabilities) by decreasing mortality risks of their host. Therefore, a parasite able to protect their host from predation when non-infective before switching to predation-increasing behavioural manipulation when infective should be selected. We tested this hypothesis in the acanthocephalan parasite Pomphorhynchus laevis in its intermediate host Gammarus pulex. Gammarids parasitized by non-infective stage of P. laevis (acanthella) hid significantly more under refuges than uninfected ones, before or after detecting predator cues. In addition, acanthella-infected gammarids were less predated upon by trout, a suitable final host, than uninfected gammarids. To our knowledge, this is the first study showing that such behavioural changes do indeed increase host survival, a necessary criterion to assign an adaptive value to this protective strategy. As predicted, a switch towards decreased anti-predatory behaviour of the host and enhanced vulnerability to predation was found when P. laevis reached the stage infective to its final host. The parasites appear to be able to exploit plasticity in host anti-predatory responses, and shift the host optimal response towards their own optimal balance. Consequences of such a protective strategy on host fitness are discussed.
    Jacques Monod Conference: "Coevolutionary arms race between parasite virulence and host immune defence: challenges from state of the art research"; 09/2011
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    ABSTRACT: Many trophically transmitted parasites with complex life cycles manipulate their intermediate host behavior in ways facilitating their transmission to final host by predation. This facilitation generally results from lowering host's antipredatory defenses when the parasite is infective to the final host. However, a recent theoretical model predicts that an optimal parasitic strategy would be to protect the intermediate host from predation when noninfective, before switching to facilitation when the infective stage is reached. We tested this hypothesis in the fish acanthocephalan parasite Pomphorhynchus laevis using the amphipod Gammarus pulex as intermediate host. Gammarids parasitized by noninfective stage of P. laevis (acanthella) hid significantly more under refuges than uninfected ones. In addition, acanthella-infected gammarids were less predated upon by trout than uninfected ones. As predicted, a switch toward decreased antipredatory behavior of G. pulex and enhanced vulnerability to predation was found when P. laevis reached the stage infective to its final host. The parasites appear to be able to exploit plasticity in host antipredatory responses, and shift the host optimal response toward their own optimal balance.
    Evolution 09/2011; 65(9):2692-8. · 4.86 Impact Factor
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    ABSTRACT: Many trophically-transmitted parasites with complex life cycle manipulate their intermediate host behaviour in ways facilitating their transmission to final host by predation, often by lowering host’s anti-predatory defences when infective to the final host. However, a recent theoretical model predicts that an optimal parasitic strategy would be to protect the intermediate host from predation when non infective, before switching to facilitation when the infective stage is reached. We tested this hypothesis in the fish acanthocephalan parasite Pomphorhynchus laevis using the amphipod Gammarus pulex as intermediate host. Gammarids parasitized by non-infective stage of P. laevis hid significantly more under refuges and were less preyed upon than uninfected ones. As predicted, a switch towards decreased anti-predatory behaviour of G. pulex and enhanced vulnerability to predation was found when P. laevis reached the stage infective to its final host. To our knowledge, this is the first study showing that such behavioural changes do indeed increase survival to predation risk, a necessary criterion to assign an adaptive value to this protective strategy. This study complements a previous one investigating intraspecific conflict between coinfecting infective and non-infective stages of P. laevis. We tested the hypothesis of a ‘sabotage’ of behavioural manipulation by the youngest non-infective parasite, and found that behavioural manipulation was slightly weakened but not cancelled in gammarids infected with mixed larval stages. Therefore, coinfecting infective and non-infective larvae both suffered competition, potentially resulting in delayed transmission and increased risk of mortality respectively. Both studies raised interesting questions about mechanisms underlying manipulation, and consequences of such strategies on host fitness.
    13th ESEB Congress (European Society for Evolutionary Biology); 08/2011
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    ABSTRACT: Parmi les parasites à transmission horizontale, certains sont dits à transmission trophique : leur transmission passe par la prédation de l’hôte intermédiaire (dans lequel ils vivent à l’état larvaire), par l’hôte définitif (dans lequel ils deviennent adultes et se reproduisent). Au sein de leur hôte intermédiaire, les parasites passent par au moins deux stades larvaires ; le premier n’est pas infectieux pour l’hôte définitif, son immaturité anatomique et physiologique l’empêchant d’infecter son hôte définitif avec succès. Le second, lui, est infectieux pour son hôte définitif. A ce stade, chez de nombreux parasites à transmission trophique, le parasite est capable de manipuler le comportement de son hôte intermédiaire. Généralement, il diminue les défenses anti-prédateur de son hôte, facilitant ainsi sa prédation par l’hôte suivant (donc sa propre transmission). Les stades larvaires non infectieux ne pouvant pas s’établir dans leur hôte définitif, un récent modèle mathématique prédit qu’une stratégie optimale pour les parasites manipulateurs serait de d’abord protéger leur hôte intermédiaire de tout risque de prédation lorsqu’ils sont non infectieux (notamment en renforçant les défenses anti-prédateur), avant de manipuler son comportement et favoriser sa prédation lorsque le stade infectieux est atteint. Nous avons testé cette hypothèse chez le parasite acanthocéphale Pomphorhynchus laevis, infectant le crustacé Gammarus pulex à l’état larvaire. Les gammares infectés par le stade non infectieux du parasite étaient significativement moins prédatés par des truites (hôtes définitifs potentiels de P. laevis) que les gammares sains. Un switch vers une prédation accrue a été trouvé lorsque P. laevis a atteint le stade infectieux pour l’hôte définitif. Ces parasites semblent ainsi en mesure d’exploiter la plasticité des réponses anti-prédateur de leur hôte crustacé, et de changer la réponse optimale de l’hôte vers leur propre intérêt.
    17ème Forum des Jeunes Chercheurs; 06/2011
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    ABSTRACT: Many trophically transmitted parasites with complex life cycles manipulate their intermediate host behavior in ways facilitating their transmission to final host by predation. This facilitation generally results from lowering host's antipredatory defenses when the parasite is infective to the final host. However, a recent theoretical model predicts that an optimal parasitic strategy would be to protect the intermediate host from predation when noninfective, before switching to facilitation when the infective stage is reached. We tested this hypothesis in the fish acanthocephalan parasite Pomphorhynchus laevis using the amphipod Gammarus pulex as intermediate host. Gammarids parasitized by noninfective stage of P. laevis (acanthella) hid significantly more under refuges than uninfected ones. In addition, acanthella-infected gammarids were less predated upon by trout than uninfected ones. As predicted, a switch toward decreased antipredatory behavior of G. pulex and enhanced vulnerability to predation was found when P. laevis reached the stage infective to its final host. The parasites appear to be able to exploit plasticity in host antipredatory responses, and shift the host optimal response toward their own optimal balance.
    Evolution 01/2011; doi: 10.1111/j.1558-5646.2011.01330.x. · 4.86 Impact Factor
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    ABSTRACT: Competitive interactions between coinfecting parasites are expected to be strong when they affect transmission success. When transmission is enhanced by altering host behaviour, intraspecific conflict can lead to 'coinfection exclusion' by the first-in parasite or to a 'sabotage' of behavioural manipulation by the youngest noninfective parasite. We tested these hypotheses in the acanthocephalan parasite Pomphorhynchus laevis, reversing phototaxis in its intermediate host Gammarus pulex. No evidence was found for coinfection exclusion in gammarids sequentially exposed to infection. Behavioural manipulation was slightly weakened but not cancelled in gammarids infected with mixed larval stages. Therefore, coinfecting infective and noninfective larvae both suffered competition, potentially resulting in delayed transmission and increased risk of mortality, respectively. Consequently, noninfective larva is not just a 'passive passenger' in the manipulated host, which raises interesting questions about the selective pressures at play and the mechanisms underlying manipulation.
    Journal of Evolutionary Biology 12/2010; 23:2648-2655. · 3.48 Impact Factor
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    ABSTRACT: Pomphorhynchus laevis, a fish acanthocephalan parasite, manipulates the behaviour of its gammarid intermediate host to increase its trophic transmission to the definitive host. However, the intensity of behavioural manipulation is variable between individual gammarids and between parasite populations. To elucidate causes of this variability, we compared the level of phototaxis alteration induced by different parasite sibships from one population, using experimental infections of Gammarus pulex by P. laevis. We used a naive gammarid population, and we carried out our experiments in two steps, during spring and winter. Moreover, we also investigated co-variation between phototaxis (at different stages of infection, 'young' and 'old cystacanth stage') and two other fitness-related traits, infectivity and development time. Three main parameters could explain the parasite intra-population variation in behavioural manipulation. The genetic variation, suggested by the differences between parasite families, was lower than the variation owing to an (unidentified) environmental factor. Moreover, a correlation was found between development rate and the intensity of behavioural change, the fastest growing parasites being unable to induce rapid phototaxis reversal. This suggests that parasites cannot optimize at the same time these two important parameters of their fitness, and this could explain a part of the variation observed in the wild.
    Journal of Evolutionary Biology 10/2010; 23(10):2143-50. · 3.48 Impact Factor
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    ABSTRACT: In parasites having a two-host life cycle, the intermediate host (IH) is used as a “vehicle” that allow parasite transmission towards definitive host (DH). As a consequence, conflicts for transmission can arise when several parasites share the same IH, given that they do not always share the same life cycles and/or the same DHs. These evolutionary conflicts between heterospecific parasites are well documented. Although less obvious at first sight, a conflict for transmission can also arise when co-interacting parasites belong to the same species. For instance, in the case of a parasite species able to manipulate its host phenotype, an intraspecific conflict for transmission can occur when parasite larvae differ in their maturity level. Indeed, by manipulating their IH behaviour, a mature larva (i.e. infectious for DH) enhances its transmission probabilities towards DH. At the opposite, an immature larva (i.e. non-infectious for DH) benefit from growing in the IH to reach maturity; thus, it does not manipulate the IH behaviour. When mature and non mature larvae co-infect the same IH, a conflict over behavioural manipulation is expected, based on opposite selection pressures for quick transmission (through host death by predation) versus growth (through host survival) of larvae. Such a conflict can either lead to a “sabotage” of behavioural manipulation from the immature larva, or to the exclusion of the second parasite by the first-infecting one. We tested these hypotheses in the acanthocephalan fish parasite Pomphorhynchus laevis using the amphipod Gammarus pulex as IH. The intensity of behavioural manipulation was slightly decreased in gammarids infected with both immature and mature larvae. Besides, our results reveal that both immature and mature larvae suffer great costs when co-existing in the same gammarid, respectively in terms of survival and transmission to the next host. Thus, the sabotage hypothesis has not been verified in our experiment. Conversely, no evidence was found for co-infection exclusion by the first-infecting larva in gammarids sequentially exposed to infection in the lab. Our results raise interesting questions about the selective pressures playing a part in the selection of optimization strategies for transmission, and the mechanisms underlying manipulation.
    Ecologie 2010; 09/2010
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    ABSTRACT: Many trophically transmitted parasites manipulate their intermediate host phenotype, resulting in higher transmission to the final host. However, it is not known if manipulation is a fixed adaptation of the parasite or a dynamic process upon which selection still acts. In particular, local adaptation has never been tested in manipulating parasites. In this study, using experimental infections between six populations of the acanthocephalan parasite Pomphorhynchus laevis and its amphipod host Gammarus pulex, we investigated whether a manipulative parasite may be locally adapted to its host. We compared adaptation patterns for infectivity and manipulative ability. We first found a negative effect of all parasite infections on host survival. Both parasite and host origins influenced infection success. We found a tendency for higher infectivity in sympatric versus allopatric combinations, but detailed analyses revealed significant differences for two populations only. Conversely, no pattern of local adaptation was found for behavioral manipulation, but manipulation ability varied among parasite origins. This suggests that parasites may adapt their investment in behavioral manipulation according to some of their host's characteristics. In addition, all naturally infected host populations were less sensitive to parasite manipulation compared to a naive host population, suggesting that hosts may evolve a general resistance to manipulation.
    Evolution 08/2010; 64(8):2417-30. · 4.86 Impact Factor
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    ABSTRACT: Parasite survival in hosts mainly depends on the capacity to circumvent the host immune response. Acanthocephalan infections in gammarids are linked with decreased activity of the prophenoloxidase (ProPO) system, suggesting an active immunosuppression process. Nevertheless, experimental evidence for this hypothesis is lacking: whether these parasites affect several immune pathways is unknown and the consequences of such immune change have not been investigated. In particular, the consequences for other pathogens are not known; neither are the links with other parasite-induced manipulations of the host. Firstly, using experimental infections of Pomphorhynchus laevis we confirmed that the lower immune activity in parasitised Gammarus pulex is induced by the parasite infection. Second, using natural infections of three different parasites, P. laevis, Pomphorhynchus tereticollis and Polymorphus minutus, we showed that acanthocephalan infection was associated with reduction of the activity of the ProPO system and the haemocyte concentration (two major parameters of crustacean immunity) suggesting that immune depression is a phenomenon affecting several immunological activities. This was confirmed by the fact that acanthocephalan infection (whatever the parasite species) was linked to a lower efficiency to eliminate a bacterial infection. The result suggests a cost of parasite immune depression. Finally, acanthocephalans are also known to induce behavioural alterations in the intermediate host which favour their transmission to definitive hosts. We did not find any correlation between behavioural and immunological alterations in both experimentally and naturally-infected gammarids. Overall, this study suggests that whilst immune depression might be beneficial to acanthocephalan survival within the intermediate gammarid host, it might also be costly if it increases host mortality to additional infections before transmission of the parasite.
    International journal for parasitology 01/2009; · 3.39 Impact Factor
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    ABSTRACT: Numerous parasites with complex life cycles are able to manipulate the behaviour of their intermediate host in a way that increases their trophic transmission to the definitive host. Pomphorhynchus laevis, an acanthocephalan parasite, is known to reverse the phototactic behaviour of its amphipod intermediate host, Gammarus pulex, leading to an increased predation by fish hosts. However, levels of behavioural manipulation exhibited by naturally-infected gammarids are extremely variable, with some individuals being strongly manipulated whilst others are almost not affected by infection. To investigate parasite age and parasite intensity as potential sources of this variation, we carried out controlled experimental infections on gammarids using parasites from two different populations. We first determined that parasite intensity increased with exposure dose, but found no relationship between infection and host mortality. Repeated measures confirmed that the parasite alters host behaviour only when it reaches the cystacanth stage which is infective for the definitive host. They also revealed, we believe for the first time, that the older the cystacanth, the more it manipulates its host. The age of the parasite is therefore a major source of variation in parasite manipulation. The number of parasites within a host was also a source of variation. Manipulation was higher in hosts infected by two parasites than in singly infected ones, but above this intensity, manipulation did not increase. Since the development time of the parasite was also different according to parasite intensity (it was longer in doubly infected hosts than in singly infected ones, but did not increase more in multi-infected hosts), individual parasite fitness could depend on the compromise between development time and manipulation efficiency. Finally, the two parasite populations tested induced slightly different degrees of behavioural manipulation.
    International Journal for Parasitology 09/2008; 38(10):1161-70. · 3.64 Impact Factor
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    ABSTRACT: Acanthocephala are parasites with complex life cycles involving arthropod intermediate hosts and vertebrate final hosts. They use predation as a means of transmission, and some species have developed the ability to modify behaviour of their intermediate hosts to enhance the probability of ingestion by the definitive host. Knowledge of how a single parasite species is adapted to modify the behaviour of different intermediate host species is important for the understanding of parasitic transmission in host communities. In Burgundy, the freshwater amphipod crustaceans Gammarus pulex (native species) and Gammarus roeseli (eastern European invader) are both intermediate hosts for the acanthocephalan Polymorphus minutus. The influence of this bird parasite on the geotaxis of G. roeseli was evaluated and it was found that when infected, individuals of this host species have a negative geotaxis compared to uninfected individuals. There were two components to the behavioural changes: swimming to the top of the water column, and clinging to surface material. These changes were comparable to those observed in the local host species G. pulex, but lower in magnitude. This result contrasts with a previous study on the influence of the fish parasite Pomphorhynchus laevis, which is able to alter the native species' behaviour, but not that of the invasive host. Parasite adaptations to local vs invasive intermediate host species are discussed in terms of their dispersal range (i.e. dispersal of their definitive hosts): the wider the dispersal, the greater should be the spectrum of intermediate hosts.
    Journal of Zoology 08/2005; 267(01):39 - 43. · 2.04 Impact Factor