Species responses to stress are expected to be dependent on their life-history strategy. In this study, we compare the responses of two free-living marine nematodes, Litoditis marina and Diplolaimella dievengatensis, both considered opportunistic, fast-growing, and stress-tolerant species, to the exposure to sublethal concentrations of sodium dodecyl sulfate (SDS) surfactant. Specifically, we evaluated the growth and reproduction rates, as well as the survival of individuals exposed from eggs and/or juveniles (J1) onwards. Exposure to SDS significantly affected the growth and reproduction rates of both species. However, whereas growth and reproduction rates of D. dievengatensis were significantly enhanced at low and intermediate concentrations of SDS (0.001% and 0.003%), for L. marina both parameters were significantly reduced by all SDS concentrations tested (0.001%, 0.003% and 0.006%). Exposure to SDS did not affect the survival of adult nematodes of D. dievengatensis, while for L. marina, survival of males exposed to 0.006% SDS was significantly reduced compared to the control. Responses of the life-history traits growth, fecundity and survival did not exhibit clear trade-offs. The contrasting responses of D. dievengatensis and L. marina indicate that biologically and ecologically similar species can have remarkably distinct tolerances to stress, and that, in agreement with recent studies, rhabditid nematodes cannot a priori be considered very stress tolerant. Consequently, single species traits and phylogenetic relatedness are poor predictors of nematode responses to toxic stress posed by anthropogenic activities.
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