Are fish immune systems really affected by parasites? an immunoecological study of common carp (Cyprinus carpio)

Rohlenová Karolína, Morand Serge, Hyršl Pavel, Tolarová Soåˆa, Flajšhans Martin, Šimková, Šimková Andrea

Description

The basic function of the immune system is to protect an organism against infection in order to minimize the fitness costs of being infected. According to life-history theory, energy resources are in a trade-off between the costly demands of immunity and other physiological demands. Concerning fish, both physiology and immunity are influenced by seasonal changes (i.e. temporal variation) associated to the changes of abiotic factors (such as primarily water temperature) and interactions with pathogens and parasites. In this study, we investigated the potential associations between the physiology and immunocompetence of common carp ( Cyprinus carpio ) collected during five different periods of a given year. Our sampling included the periods with temporal variability and thus, it presented a different level in exposure to parasites. We analyzed which of two factors, seasonality or parasitism, had the strongest impact on changes in fish physiology and immunity. Results We found that seasonal changes play a key role in affecting the analyzed measurements of physiology, immunity and parasitism. The correlation analysis revealed the relationships between the measures of overall host physiology, immunity and parasite load when temporal variability effect was removed. When analyzing separately parasite groups with different life-strategies, we found that fish with a worse condition status were infected more by monogeneans, representing the most abundant parasite group. The high infection by cestodes seems to activate the phagocytes. A weak relationship was found between spleen size and abundance of trematodes when taking into account seasonal changes. Conclusions Even if no direct trade-off between the measures of host immunity and physiology was confirmed when taking into account the seasonality, it seems that seasonal variability affects host immunity and physiology through energy allocation in a trade-off between life important functions, especially reproduction and fish condition. Host immunity measures were not found to be in a trade-off with the investigated physiological traits or functions, but we confirmed the immunosuppressive role of 11-ketotestosterone on fish immunity measured by complement activity. We suggest that the different parasite life-strategies influence different aspects of host physiology and activate the different immunity pathways.

Informations

• Publié par: biomed
• Publié le: 01 janvier 2011
• Nombre de lectures: 10
• Langue: English

Extrait

Rohlenováet al.Parasites & Vectors2011,4:120 http://www.parasitesandvectors.com/content/4/1/120

R E S E A R C HOpen Access Are fish immune systems really affected by parasites? an immunoecological study of common carp (Cyprinus carpio) 1 23 34 1* Karolína Rohlenová , Serge Morand , Pavel Hyršl , Soňa Tolarová , Martin FlajšAndreahans andŠimková

Abstract Background:The basic function of the immune system is to protect an organism against infection in order to minimize the fitness costs of being infected. According to lifehistory theory, energy resources are in a tradeoff between the costly demands of immunity and other physiological demands. Concerning fish, both physiology and immunity are influenced by seasonal changes (i.e. temporal variation) associated to the changes of abiotic factors (such as primarily water temperature) and interactions with pathogens and parasites. In this study, we investigated the potential associations between the physiology and immunocompetence of common carp (Cyprinus carpio) collected during five different periods of a given year. Our sampling included the periods with temporal variability and thus, it presented a different level in exposure to parasites. We analyzed which of two factors, seasonality or parasitism, had the strongest impact on changes in fish physiology and immunity. Results:We found that seasonal changes play a key role in affecting the analyzed measurements of physiology, immunity and parasitism. The correlation analysis revealed the relationships between the measures of overall host physiology, immunity and parasite load when temporal variability effect was removed. When analyzing separately parasite groups with different lifestrategies, we found that fish with a worse condition status were infected more by monogeneans, representing the most abundant parasite group. The high infection by cestodes seems to activate the phagocytes. A weak relationship was found between spleen size and abundance of trematodes when taking into account seasonal changes. Conclusions:Even if no direct tradeoff between the measures of host immunity and physiology was confirmed when taking into account the seasonality, it seems that seasonal variability affects host immunity and physiology through energy allocation in a tradeoff between life important functions, especially reproduction and fish condition. Host immunity measures were not found to be in a tradeoff with the investigated physiological traits or functions, but we confirmed the immunosuppressive role of 11ketotestosterone on fish immunity measured by complement activity. We suggest that the different parasite lifestrategies influence different aspects of host physiology and activate the different immunity pathways.

Background Physiology and immunity in fish, a group of poikilother mic vertebrates, are strongly influenced by both abiotic and biotic factors. Water temperature is generally con sidered as the strongest abiotic factor which affects fish physiology including immune functions. However, the infection dynamics of fish parasites and pathogens is

* Correspondence: [e-mail] 1 Department of Botany and Zoology, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic Full list of author information is available at the end of the article

also strongly influenced by water temperature changes [1,2]. To determine whether the observed status of fish phy siology results from abiotic changes or reflects the level of parasite infestation is very difficult in natural condi tions because of the confounding effects of several abio tic and biotic factors including parasitism, often varying in space and time. Recently, many studies have focused on the abiotic effects, especially of water temperature, on physiological and immunological mechanisms in poi kilothermic organisms, like fish. The majority of

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