Parasite-induced inversion of geotaxis in a freshwater amphipod: a role for anaerobic metabolism?

9 pagesInternational audience1. Many parasites with complex life cycles alter the phenotype of their intermediate hosts inways that seem to favour transmission to a final host. Although there is a large literature onhost manipulation, how parasites alter the phenotype of their hosts remains poorly known.2. The bird acanthocephalan Polymorphus minutus is known to alter geotaxis in its amphipodhost, Gammarus roeseli. Here, we examine the potential roles of low oxygen availability andthe excretion, by the parasite, of two products from its own anaerobic metabolism (lactate andsuccinate) in altered geotaxis.3. Under hypoxia, uninfected G. roeseli showed negative geotaxis and lower metabolic rate,two traits also altered by infection with P. minutus, albeit with different intensities. Theinjection of a mixture of lactate and succinate in uninfected amphipods mimicked theparasite-induced reversion of geotaxis, without affecting the metabolic rate.4. In addition, both P. minutus-infected gammarids and uninfected ones conditioned tohypoxia for 2 days showed elevated levels of lactate in the brain, but not in the haemolymph.5. Overall, our results indicate that the pathways involved in anaerobic metabolism andhypoxia signalling might be responsible for the changes in geotaxis and metabolic rate inducedby P. minutus infection.6. Our study emphasizes the need to consider the tight and complex connections between physiologicalprocesses and behavioural adjustments, in particular at the brain level, in the understandingof parasitic manipulation, and more broadly of behavioural changes in infected hosts