What fraction of the organic carbon in sacoglossans is obtained from photosynthesis by kleptoplastids? An investigation using the natural abundance of stable carbon isotopes |
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Authors: | J A Raven D I Walker K R Jensen L L Handley C M Scrimgeour S G McInroy |
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Institution: | Division of Environmental and Applied Biology, School of Life Sciences, University of Dundee, Dundee DD1 4HN, UK e-mail: j.a.raven@dundee.ac.uk, GB Department of Botany, The University of Western Australia, Nedlands WA6907, Australia, AU Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK, GB
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Abstract: | any sacoglossans (opisthobranch gastropods) have the potential for carbon acquisition from photosynthesis by plastids sequestered
from their macroalgal food as well as by ingestion, digestion and assimilation of the organic carbon derived from the alga.
A new method for obtaining a minimum estimate of the fraction of sacoglossan carbon supplied from photosynthesis by kleptoplastids
is suggested, based on the mass balance of stable carbon isotopes at the natural abundance level. The method involves comparison
of 13C/12C ratios in sacoglossans with those of the algae on which they are found. Differences in ratios between alga and sacoglossan
are used to give a minimum estimate of carbon acquisition by kleptoplasty, granted assumptions about the range of 13C/12C fractionation values which can occur for marine photolithotrophs. The new method is applied to several green (ulvophycean)
alga–sacoglossan associations from Rottnest Island, Western Australia, and the values compared with those obtained previously
by other means. The method suggests values of up to 0.6 of the total carbon input to the sacoglossans from photosynthesis
by their kleptoplastids. To improve the estimates of the minimum role of kleptoplastidy in the carbon nutrition of sacoglossans,
further information is needed: (1) on the fidelity of a given sacoglossan to a given algal individual (or species), (2) on
the 13C/12C ratio of the part of the alga ingested by the sacoglossan, and (3) on the allocation of dietary organic carbon and of kleptoplastidic
photosynthate to carbon lost in respiration, mucopolysaccharide production and gametes (and hence not sampled with the animal).
Received: 24 November 1999 / Accepted: 20 October 2000 |
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