Fluctuating versus constant temperatures: effects on metabolic rate and oxidative damages in freshwater crustacean embryos

Rising temperatures will pose a major threat, notably for freshwater ecosystems, in the decades to come. Temperature, a major environmental factor, affects organisms’ physiology and metabolism. Most studies of temperature effect address constant thermal regime (CTR), whereas organisms are exposed to fluctuating thermal regime (FTR) in their natural environments. In addition, previous works have predominantly addressed issues of thermal tolerance in adults rather than in early life stages. Therefore, for the first time to our knowledge, we aimed to investigate the influence of thermal conditions, either FTR or CTR, on the physiology of the crustacean amphipod Gammarus roeseli Gervais, 1835 at different embryonic stages. We measured the metabolic rate and the TBARS (thiobarbituric acid reactive substances) body content (to assess the level of oxidative damage). Oxygen consumption rate strongly increased throughout embryo development, whereas oxidative damages did not clearly change. In addition, the embryos tended to consume oxygen equally but displayed less oxidative damage when developing under FTR compared with developing under CTR. Moreover, our results revealed that fluctuating temperatures (and especially the existence of a colder (nonstressful) period during the day) could allow cell-damage repairs, and therefore, allow G. roeseli embryos to ensure good development by implementing an efficient protection response against oxidative stress.

Identifying a key host in an acanthocephalan-amphipod system

SUMMARYTrophically transmitted parasites may use multiple intermediate hosts, some of which may be ‘key-hosts’, i.e. contributing significantly more to the completion of the parasite life cycle, while others may be ‘sink hosts’ with a poor contribution to parasite transmission. Gammarus fossarum and Gammarus roeseli are sympatric crustaceans used as intermediate hosts by the acanthocephalan Pomphorhynchus laevis. Gammarus roeseli suffers higher field prevalence and is less sensitive to parasite behavioural manipulation and to predation by definitive hosts. However, no data are available on between-host differences in susceptibility to P. laevis infection, making it difficult to untangle the relative contributions of these hosts to parasite transmission. Based on results from estimates of prevalence in gammarids exposed or protected from predation and laboratory infections, G. fossarum specimens were found to be more susceptible to P. laevis infection. As it is more susceptible to both parasite infection and manipulation, G. fossarum is therefore a key host for P. laevis transmission.