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

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