Abstract
Solar-powered sea slugs (Sacoglossa: Gastropoda) have long captured the attention of laymen and scientists alike due to their remarkable ability to steal functional chloroplasts from their algal food, enslaving them to withstand long starvation periods. Recently, a wealth of data has shed insight into this remarkable relationship; however, the cellular mechanisms governing this process are still completely unknown. This study explores these mechanisms, providing insight into the chloroplast retention and delayed digestion, occurring within the slug’s digestive gland. We examine the relationships between functional chloroplast and lysosome abundances during starvation, in live material, for the long-term retaining species Elysia timida, the ambiguous long/short-term retaining Elysia viridis, and the short-term retaining Thuridilla hopei, to elucidate digestive differences that contribute to the development of functional kleptoplasty. Functional chloroplast and lysosome abundance are measured using chlorophyll a autofluorescence and the pH-dependent stain acridine orange. In each species, the number of chloroplasts and lysosomes is indirectly proportional, with the plastid density decreasing when starvation begins. We also present a new FIJI/Image J Plugin, the 3D—Accounting and Measuring Plugin, 3D-AMP, which enables the reliable analysis of large image sets.
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Acknowledgments
We would like to thank Claudia Müller, Jörn van Döhren, Ekin Tilic, Daria Krämer, Albert Haas, Gregor Christa, Cessa Rauch, Jan de Vries, and Sven Gould and Ulf Bickmeyer for their expertise and help in this project. We also appreciate the feedback we received from our two anonymous reviewers.
This study was funded by the Deutsche Forschungsgemeinschaft project Wa 618/17, the Alexander Koenig Gesellschaft, and a personal grant to EMJL from the University of Bonn, Germany.
Author contributions
EMJL and HW devised the project concept and EMJL conducted the lab work. PTR and EMJL designed 3D-AMP and PTR wrote this software. AP and TB help troubleshoot staining and all authors contributed to the analysis and manuscript.
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Laetz, E.M.J., Rühr, P.T., Bartolomaeus, T. et al. Examining the retention of functional kleptoplasts and digestive activity in sacoglossan sea slugs. Org Divers Evol 17, 87–99 (2017). https://doi.org/10.1007/s13127-016-0308-0
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DOI: https://doi.org/10.1007/s13127-016-0308-0