Summary Reduced metabolic rates of groundwater taxa, compared to those of surface water species, have long been inferred to be an adaptive trait where there is a low and discontinuous food supply and unpredictable shifts between hypoxic and normoxic conditions. However, there have been neither measurements of the respiratory rate of groundwater copepods nor a comparison of rates between closely related groundwater and surface water species. We measured the metabolic rates of two species of Cyclopoida: Cyclopidae, the stygobiotic (hypogean) copepod Diacyclops belgicus and the epigean Eucyclops serrulatus, which co‐occur in the same alluvial aquifer. We expected the metabolic rate of the hypogean to be lower than that of the epigean species, irrespective of the ontogenetic stage, which would be consistent with the hypothesis that there is a generally lower metabolic rate in groundwater species. The metabolic rate of D. belgicus was significantly lower than that of the epigean E. serrulatus irrespective of the ontogenetic stage. We found an allometric relationship between oxygen consumption and body mass for E. serrulatus, an isometric one for D. belgicus juveniles and a rate of oxygen consumption that apparently does not change systematically with body mass for D. belgicus adults. The low metabolic rate of D. belgicus may be advantageous in oligotrophic groundwater habitats, where large fluctuations in oxygen availability occur. However, these physiological adaptations can put hypogean species at risk of replacement by more metabolically active epigean taxa, whenever the availability of organic matter increases, as happens with organic pollution. Moreover, the low metabolic rate of the hypogean species may entail an inability to cope with toxicants, rendering them more sensitive to pollutants. A higher metabolic rate in juvenile D. belgicus compared to that of adults allows copepodids to mature quickly when food is briefly abundant.

International audienceClimate warming often leads to shifts in the strength and sign of agonistic interactions among species, which in turn may change their distribution ranges. Notwithstanding the ubiquity of this phenomenon, there is scant literature about how interspecific agonistic behaviour changes with altered thermal regime, especially for invasive species such as three widespread North American crayfishes in Europe (Orconectes limosus, Procambarus clarkii and Pacifastacus leniusculus). * We conducted a laboratory study to analyse some descriptors of agonistic behaviour in fighting dyads of similarly sized males of the three species' combinations, both at 20 °C (the current maximum water temperature in the study area, central France) and 27 °C (the maximum expected in the next 80 years under the more pessimistic IPCC greenhouse gas emission scenario). * The results showed significantly different responses to warming by the three crayfishes. At 27 °C, O. limosus spent more time motionless and P. leniusculus was more often the subordinate, independent of the opponent. On the contrary, the agonistic strategy of P. clarkii did not change with temperature: when engaged in fighting, this species outcompeted both O. limosus and P. leniusculus. * Caution should be taken when extrapolating laboratory studies to the field, but these results, combined with outputs of previous modelling exercises, suggest that European catchments will become dominated by P. clarkii with climate warming. Ultimately, this might lead to impoverished biodiversity, simplified food webs and altered ecosystem services

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The American red swamp crayfish, Procambarus clarkii, is today the alien species most widespread in European water bodies. This invasive crayfish was found for the first time in some caves of Europe, specifically in Portugal and Italy. The presence of P. clarkii in caves is noteworthy, representing a new threat for the groundwater ecosystems due to the possible negative impacts on the native communities.