Fig. 2

Daily fluctuating temperature reduces Bd growth, zoospore production, and zoosporangia viability but not culture fecundity compared to Bd grown at an optimal temperature. a Daily optical density measurements of Bd cultures suggest differences in maximum growth and logistic growth rate among cultures incubated at 17.5 °C (green), 27.5 °C (red), and fluctuating temperatures (black). OD readings of cultures grown at 7.5 °C (blue) did not follow a pattern of logistic growth. Points represent means (n = 16 treatment⁻¹ day⁻¹). b Zoospore production differed among Bd cultures grown at constant (7.5 °C, 17.5 °C, or 27.5 °C) and fluctuating temperatures. Cultures grown at 17.5 °C had the highest maximum zoospore production (ANOVA, P < 0.001). Cultures grown at 7.5 °C had similar maximum zoospore production as cultures grown under fluctuating temperatures (Tukey HSD, P = 0.99) but reached peak production later. Cultures grown at 27.5 °C did not produce zoospores. Points represent mean counts of motile zoospores (n = 6 treatment⁻¹ day⁻¹). c Fluctuating and optimal temperature cultures did not differ in fecundity. Culture fecundity was measured as the ratio of motile zoospores to total culture growth (OD) day⁻¹. Despite reduced total growth (OD), cultures grown at 7.5 °C had higher fecundity than cultures grown at 17.5 °C or fluctuating temperatures (ANOVA, P < 0.001). Cultures grown at 27.5 °C did not produce zoospores. Dashed vertical lines correspond to time of peak zoospore production in fluctuating (day 8), 17.5 °C (day 10), and 7.5 °C (day 14) cultures. Points represent means (n = 6 treatment⁻¹ day⁻¹). d Zoosporangia viability differed among Bd cultures grown at fluctuating and constant temperatures. Cultures grown under fluctuating temperatures had lower zoosporangia viability than cultures grown at 17.5 °C but higher viability than cultures grown at 7.5 °C or at 27.5 °C (Kruskal–Wallis, P < 0.001). Points represent means (n = 8 treatment⁻¹ day⁻¹). In all panels, error bars represent standard error and letters indicate significant differences