Full compensation of growth in salt-tolerant tadpoles after release from salinity stress

The benefit of compensatory growth is to minimize the negative effects of stress experienced by organisms early in development once the conditions improve. Tadpoles of crab-eating frog Fejervarya cancrivora are euryhaline, have the highest salt tolerance among reported anuran species and may exhibit a different pattern of compensatory growth after stress release. We examined how F. cancrivora tadpoles responded and possibly recovered from salinity stresses. Specifically, we tested whether tadpoles expressed compensatory growth, what degree of compensation they expressed after release from salinity stress and whether the stage at and duration during which they experienced salt stress influenced the size at and time to metamorphosis of tadpoles. We found that the effects of salinity stress on the growth and development of tadpoles are quite different between early and late exposure to high salinity (LHH vs. LLH). Exposure to high salinity late in development (LLH) reduced growth but not the rate of development, resulting in smaller metamorphs but a similar time to metamorphosis when compared to the control treatment (LLL). By contrast, exposure to high salinity early in development (LHH) retarded rates of growth and development of tadpoles, but the resulting prolonged larval period enabled tadpoles to catch up and reach similar metamorphic sizes to LLL treatment metamorphs. Most importantly, tadpoles released from salinity stress (LHL) exhibited similar time to and size at metamorphosis when compared to the LLL tadpoles, suggesting that they can exhibit full compensation of growth. Compensatory growth may be a useful mechanism for F. cancrivora tadpoles inhabiting brackish habitats, allowing them to overcome the effects of dramatically increased salt levels by expressing catch-up growth when the salt stress ceases.