RESUMEN
Parasites represent a ubiquitous threat for most organisms, requiring potential hosts to invest in a range of strategies to defend against infection-these include both behavioural and physiological mechanisms. Avoidance is an essential first line of defence, but this behaviour may show a trade-off with host investment in physiological immunity. Importantly, while environmental stressors can lead to elevated hormones in vertebrates, such as glucocorticoids, that can reduce physiological immunity in certain contexts, behavioural defences may also be compromised. Here, we investigate anti-parasite behaviour and immune responses against a trematode (flatworm) parasite by larval amphibians (tadpoles) exposed or not to a simulated general stressor in the form of exogenous corticosterone. Tadpoles that were highly active in the presence of the trematode infectious stage (cercariae) had lower infection loads, and parasite loads from tadpoles treated only with dechlorinated water were significantly lower than those exposed to corticosterone or the solvent control. However, treatment did not affect immunity as measured through white blood-cell profiles, and there was no relationship between the latter and anti-parasite behaviour. Our results suggest that a broad range of stressors could increase host susceptibility to infection through altered anti-parasite behaviours if they elevate endogenous glucocorticoids, irrespective of physiological immunity effects. How hosts defend themselves against parasitism in the context of multiple challenges represents an important topic for future research, particularly as the risk posed by infectious diseases is predicted to increase in response to ongoing environmental change.
Asunto(s)
Corticosterona , Interacciones Huésped-Parásitos , Larva , Animales , Trematodos/fisiología , Conducta Animal , GlucocorticoidesRESUMEN
Lipids, particularly fatty acids (FAs), are major sources of energy and nutrients in aquatic ecosystems and play key roles during vertebrate development. The European eel Anguilla anguilla goes through major biochemical and physiological changes throughout its lifecycle as it inhabits sea- (SW), and/or brackish- (BW) and/or freshwater (FW) habitats. With the ultimate goal being to understand the reasons for eels adopting a certain life history strategy (FW or SW residency vs. 'habitat shifting'), we explored differences in lipid content and FA composition of muscle, liver and eyes from eels collected across Norwegian SW, BW and FW habitats, and at different lifecycle stages (yellow to silver). FW and SW eels had a higher lipid content overall compared to BW eels, reflecting differences in food availability and life history strategies. SW eels had higher proportions of certain monounsaturated FAs (MUFAs; 18:1n-9, 20:1n-9), and of the essential polyunsaturated FAs 20:5n-3 (eicosapentaenoic acid, EPA) and 22:6n-3 (docosahexaenoic acid) than FW eels, reflecting a marine-based diet. In contrast, the muscle of FW eels had higher proportions of 18:3n-3, 18:2n-6 and 20:4n-6 (arachidonic acid), as is typical of FW organisms. MUFA proportions increased in later stage eels, consistent with the hypothesis that the eels accumulate energy stores prior to migration. In addition, the decrease of EPA with advancing stage may be associated with the critical role that this FA plays in eel sexual development. Lipid and FA information provided further understanding of the habitat use and overall ecology of this critically endangered species.
Asunto(s)
Anguilla , Ecosistema , Anguilla/metabolismo , Anguilla/fisiología , Animales , Ácidos Grasos , Agua DulceRESUMEN
Eutrophication of aquatic habitats has become a global problem, with implications for host-parasite dynamics. Blooms of certain cyanobacteria are associated with cyanotoxins, particularly microcystins such as microcystin-LR (MC-LR). These potent toxins have been shown to adversely affect freshwater fauna and can increase host susceptibility to parasite infection. However, to understand how cyanotoxins influence infection outcomes in nature, it is necessary to investigate whether free-living parasite infectious stages, such as that of trematode cercariae, are also affected given their demonstrated sensitivity to various contaminants. Here we examined the effects of environmentally relevant levels of MC-LR representing relatively high (82 µg/L) and low (11 µg/L) concentrations on the activity and survival of four different types of cercariae ( Echinostoma sp., Cephalogonimus sp., Alaria sp., and an unidentified strigeid type) over 24 hr. Exposure to MC-LR did not affect the activity of any cercarial type, nor was survival reduced. In fact, the strigeid-type cercariae had significantly increased longevity if exposed to either MC-LR solution, with the greatest longevity in the highest concentration. Our results indicate that MC-LR may have opposing effects on aquatic parasites and their hosts, potentially increasing host susceptibility but having a neutral or positive effect on motile infectious stages such as cercariae. Cyanobacterial blooms could thus enhance trematode transmission; however, the effects of other cyanotoxins must be studied, as well as a broader range of host and parasite species.
Asunto(s)
Toxinas Bacterianas/toxicidad , Toxinas Marinas/toxicidad , Microcistinas/toxicidad , Trematodos/efectos de los fármacos , Animales , Cercarias/efectos de los fármacos , Toxinas de Cianobacterias , Relación Dosis-Respuesta a Droga , Echinostoma/efectos de los fármacos , Eutrofización , Modelos Lineales , Estanques , Caracoles/parasitologíaRESUMEN
Anthropogenic activities are promoting the proliferation of aquatic primary producers in freshwater habitats, including cyanobacteria. Among various problems stemming from eutrophication, cyanobacterial blooms can be toxic due to the production of secondary compounds, including microcystins such as microcystin-LR (MC-LR); however, it is unknown whether cyanotoxins can affect the susceptibility of aquatic vertebrates such as fish and larval amphibians to parasites or pathogens even though infectious diseases can significantly affect natural populations. Here, we examined how exposure to environmentally relevant concentrations of MC-LRs affected the resistance of larval amphibians (northern leopard frog, Rana pipiens) to infection by a helminth parasite (the trematode Echinostoma sp.), and whether this was manifested by reductions in host anti-parasite behavior. Exposure to a relatively high (82 µg L-1) concentration of MC-LR caused over 70% mortality, and tadpoles that survived exposure to the low MC-LR (11 µg L-1) treatment had significantly higher infection intensities than those in the control; however, anti-parasite behavior was not affected by treatment. Our results indicate that MC-LR can have both direct and indirect negative effects on larval amphibians by increasing their mortality and susceptibility to parasitism, which may have implications for other aquatic vertebrates in eutrophic habitats dominated by cyanobacteria as well.
Asunto(s)
Toxinas Bacterianas/farmacología , Echinostoma/efectos de los fármacos , Equinostomiasis/veterinaria , Larva/parasitología , Toxinas Marinas/farmacología , Microcistinas/farmacología , Rana pipiens/parasitología , Animales , Cianobacterias/metabolismo , Toxinas de Cianobacterias , Equinostomiasis/parasitología , Ecosistema , Eutrofización , Agua Dulce/microbiologíaRESUMEN
Large quantities of road salts are used for de-icing in temperate climates but often leach into aquatic ecosystems where they can cause harm to inhabitants, including reduced growth and survival. However, the implications of road salt exposure for aquatic animal susceptibility to pathogens and parasites have not yet been examined even though infectious diseases can significantly contribute to wildlife population declines. Through a field survey, we found a range of NaCl concentrations (50-560mg/L) in ponds known to contain larval amphibians, with lower levels found in sites close to gravel- rather than hard-surfaced roads. We then investigated how chronic exposure to environmentally-realistic levels of road salt (up to 1140mg/L) affected susceptibility to infection by trematode parasites (helminths) in larval stages of two amphibian species (Lithobates sylvaticus - wood frogs, and L. pipiens - northern leopard frogs) by considering effects on host anti-parasite behavior and white blood cell profiles. Wood frogs exposed to road salt had higher parasite loads, and also exhibited reduced anti-parasite behavior in these conditions. In contrast, infection intensity in northern leopard frogs had a non-monotonic response to road salts even though lymphocytes were only elevated at the highest concentration. Our results indicate the potential for chronic road salt exposure to affect larval amphibian susceptibility to pathogenic parasites through alterations of behavior and immunocompetence, with further studies needed at higher concentrations, as well as that of road salts on free-living parasite infectious stages.