Photosynthetic efficiency and kleptoplast pigment diversity in the sea slug Thuridilla hopei (Vérany, 1853)

Sacoglossan species have been widely investigated due to their capacity for retaining chloroplasts within cells contained in the tubules of their digestive gland. However, there remains a gap in the literature concerning the photosynthetic pigments involved and their functionality, particularly in species with short-term retention times. Thuridilla hopei is one such species and hence the focus of this investigation. The current study attempted to 1) identify and quantify kleptoplast pigment composition, 2) determine pigment functionality and 3) analyze the photosynthetic efficiency of T. hopei. Our results show for the first time T. hopei kleptoplast pigment composition and detected two potential algae food sources for the species. Pigments show a limited functionality since they have a turnover rate of approximately 48 h, during which time chlorophylls appear to be the pigments with the fastest degradation rate (90 to 95% by the end of starvation period). Throughout starvation treatments, photosynthetic efficiency decreased and became further limited as pigment degradation increased. Ultimately, the photosynthetic electron transport chain became inactive after one day of starvation. Overall, algal chloroplasts performed better than kleptoplasts in T. hopei.

► Inside the animal pigments have a 48 h turnover rate.
► Chlorophylls degraded at a faster rate than other pigments.
► Photosynthetic efficiency was low and restricted by increase in pigment degradation.
► Electron transport chain was inactive after one day of starvation.