Abstract
Salinity conditions experienced by organisms in coastal regions may shape their life histories. Here, salinity’s impact on reproduction and survival of the hydrozoan Eleutheria dichotoma was investigated using laboratory-cultured individuals originating from Banyuls-sur-Mer (southern France) collected several decades ago. During the experiment (October 2014–July 2015), hydroid colonies and medusae were exposed to three salinities (25, 35, 45). Asexually budded medusae were collected from colonies and reared for three generations obtained by asexual budding of medusae. Salinities experienced by hydroid colonies had only minor effects on initial size, time to maturity, medusa budding, sexual production of planulae by medusae, and survival. In contrast, salinities experienced by medusae influenced their life histories. Compared with medium salinity (35), low-salinity medusae (25) had an earlier onset and higher rates of asexual budding, a later onset and slower rates of sexual reproduction, and higher mortality, which could result from allocation tradeoffs. The increased production of planulae by medusae in low salinity indicated that they were transitioning to a benthic polyp life form more resistant to environmental stress. High salinity (45) delayed asexual maturity, prevented sexual maturity in medusae, and led to lower survival and asexual reproduction rates. Budding rates decreased across the generations; however, planula production rates decreased in medium salinity but increased in low salinity. This might be explained by the accumulation of damage with each generation, and/or by internal rhythms. The flexible responses of this tractable model organism, Eleutheria dichotoma, to salinity change may be useful in future studies on changing estuarine conditions.
Highlights
Temperature and salinity are key factors affecting the physiological and ecological responses of organisms inhabiting estuaries and brackish waters (e.g., Kinne 1970; Remane and Schlieper 1972)
The median age at asexual maturity for all medusae reared in medium salinity (35), for the pooled effects of salinity experienced by hydranths (excluding H45M35 treatment—hydroid colony (H) reared at salinity 45, medusae (M) reared at salinity 35), was estimated at 11 days in G1 (11.5 days for H25M35G1 and 10.5 days for H35M35G1), 18.5 days in G2 (20 days for H25M35G2 and 18.5 days for H35M35G2), and 26 days in G3 (29.5 days for H25M35G3 and 22.5 days for H35M35G3)
The reference was set as H35M35G1 (hydroid colony reared in salinity 35 (H35), medusae reared in salinity 35 (M35), first generation (G1)
Summary
Temperature and salinity are key factors affecting the physiological and ecological responses of organisms inhabiting estuaries and brackish waters (e.g., Kinne 1970; Remane and Schlieper 1972). While water temperature varies seasonally, Aleksandra Dańko and Maciej J. Changes in salinity can cause osmotic stress, which is associated with cell shrinkage or lysis. Cell volume regulation is a mechanism for coping with osmotic stress on the cellular level (Hoffmann and Pedersen 2011). The physiological regulation of cell volume involves osmoregulation (ionic regulation of intra- and extracellular fluids through ion channels, ion exchange proteins, or primary ion pumps) and osmotic
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