Understanding kleptoplasty in Sacoglossa (Heterobranchia, Gastropoda) - a cellular histochemical and genomic approach
Systematics and Morphology (Zoology)
Final Report Abstract
Sacoglossan sea slugs are the only metazoans known to sequester and retain functional chloroplasts within their digestive gland tubules, a process known as functional kleptoplasty. This ability coincides with the capacity to withstand extended starvation periods – some species even achieving 3-12 months without access to food. Sequestered chloroplasts have been examined throughout the starvation periods of sacoglossan species, comparing species that can withstand extended starvation and such that cannot. We found that only the long-term plastid retaining species contain chloroplasts that produce starch when living in the slug’s tissue. Using Acridine orange staining for lysosomes in multiple species, we looked at intracellular digestion in these animals and could observe different digestive activity trends for species with long-term plastid retention and species with short-term plastid retention. We could provide evidence as to how some species regulate their own digestive activity to withstand starvation by digesting the chloroplasts during starvation. This is indicated by an inversely proportional relationship, where the number of chloroplasts decreases as the animals starve and the number of lysosomes increases. We could clearly show that chloroplasts fulfill their tasks inside the slug’s cells and produce photosynthates, which accumulate in amylose/starch granules. Chloroplast degradation and lysosomal activity clearly correlate and allow the assumption, that chloroplasts are finally digested and starch becomes available to the slug as an additional food source. We still do not know, how the chloroplasts are incorporated into the slugs’ cells and how they are digested. This is due to the lack of adequate methodologies, because questions like the ones outlined here, are never investigated in gastropods but usually in model taxa of vertebrates.
Publications
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2017 Examining the retention of functional kleptoplasts and digestive activity in sacoglossan sea slugs. Organisms, Diversity & Evolution
Laetz Emj, Rühr P, Bartolomaeus T, Preisfeld A, Wägele H
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(2017) Chloroplast digestion and the development of functional kleptoplasty in juvenile Elysia timida Risso, 1818 as compared to short-term and non-chloroplast-retaining sacoglossan slugs. Plos One
Laetz, Emj, Wägele H
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(2017) Photosynthate accumulation in solar-powered sea slugs - starving slugs survive due to accumulated starch reserves. Frontiers in Zoology 14:4
Laetz EMJ, Moris VC, Moritz LM, Haubrich AN, Wägele H
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(2018) Comparing amylose production in two solar-powered sea slugs: the sister taxa Elysia timida and Elysia cornigera (Heterobranchia: Sacoglossa). J Moll Stud 1-6
Laetz EMJ, Wägele H
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How does Temperature affect functional kleptoplasty? Cmparing populations of the Solar-powered Sea Slug Sister-species Elysia timida Risso, 1818 and Elysia cornigera Nuttal, 1989 (Gastropoda: Sacoglossa). Front in Zool
Laetz EMJ, Wägele H
