Fig. 16

Comparison of isotopic results for Eocene species and modern cultured photosymbiotic species. a Chamber-by-chamber δ¹³C versus cumulative test mass of Eocene species. The same shade is used for symbols of the same species (black: Morozovella crater; gray: Acarinina cuneicamerata; white: Subbotina eocaena). Data for the same individual are connected in ontogenetic order. Error bars represent analytical errors (± 0.1‰). Each individual test was dissected into chambers using a micro-blade (e.g., Takagi et al. 2015; 2016b), then analyzed by a customized continuous-flow mass spectrometry system that can measure micro-volume carbonate as small as a single chamber (Ishimura et al. 2004, 2008). Symbiotic species Morozovella and Acarinina tended to show slight positive shifts until the penultimate chamber and then the final chamber showed drastically more ¹³C-depleted δ¹³C (values 0.5–1.0‰). In contrast to these species, Subbotina showed comparatively ¹³C-depleted δ¹³C values through its ontogeny, which is in good agreement with the known non-symbiotic nature of this species. b Growth and test isotopic results for the modern symbiotic species Globigerinoides sacculifer cultured in a laboratory (Takagi et al., 2018). Chlorophyll-a content of the individual was estimated using an active chlorophyll fluorometry in a non-destructive manner. After the gametes release, chambers precipitated during culture were dissected and δ¹³C and δ¹⁸O were analyzed. Data are partly from Takagi et al. (2016a). The decrease of δ¹³C was accompanied by a decrease in (or almost zero) photosynthesis at the final stage, indicating that the lack of photosynthesis could be clearly depicted from the chamber-by-chamber isotopic profiles