Dataset: Cell-growth gene expression reveals a direct fitness cost of grazer-induced toxin production in red tide dinoflagellate prey

Refer to the Methods section of Park & Dam (2021).

Sample collection and culture:
The toxigenic dinoflagellate, Alexandrium catenella (strain BF-5, isolated from the Bay of Fundy, Canada) was grown in F/2 medium without silicate. Cultures were maintained in the exponential growth phase and all experiments were conducted in an environmental chamber kept at 18°C and illuminated with fluorescent lighting (~100 µM m⁻² s⁻¹) set to a 12 h:12 h light:dark photoperiod. The calanoid copepod Acartia hudsonica, historically co-occurring with toxic A. catenella, was collected from Casco Bay, Maine, U.S.A. (43°39′N, 74°47′W), a location in which blooms of A. catenella are common. Triplicate copepod cultures were maintained with a mixed diet of Rhodomonas sp., Tetraselmis sp., and Thalassiosira weissflogii.

Grazer-induced toxin production assay:
Alexandrium catenella cells were placed in 500 ml bottles (300 cells ml⁻¹) either without copepods (controls: constitutive toxin production) or with 20 adult female A. hudsonica (treatments) for a period of 96 h. Experiments were done in quadruplicate sets for both control and treatment, and carried out at 18 °C in a walk-in environmental chamber as described above. For the time series analysis, A. catenella cells were harvested at the conclusion of each exposure time (0, 4, 8, 24, 48, 72, and 96 h) after which cells were gently separated by wet-sieving onto a 63 μm mesh to remove copepods, nauplii, eggs, and fecal pellets. Two aliquots from each bottle were filtered onto 5 μm pore size polycarbonate membranes; one for toxin analysis and another for RNA extraction.

Toxin and gene expression analysis:
PST concentrations were determined by reverse-phase ion-pairing high performance liquid chromatography (HPLC) using the post-column oxidative fluorescence method. Gene expression analyses were conducted using reverse transcription quantitative PCR (RT-qPCR). From previous studies several pairs of primers were designed and tested for specificity and PCR efficiency by RT-qPCR. All quantitative PCRs (qPCRs) were performed on a StepOnePlus™ real-time PCR system (Applied Biosystems) and run in 10 μL reactions with Fast SYBR® Green Master Mix (Applied Biosystems).