Same HostPlant Different Sterols Variation in S

Authors: Eric M Janson Robert J Grebenok Spencer T Behmer Patrick Abbot

Publish Date: 2009/11/27

Volume: 35, Issue: 11, Pages: 1309-

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Abstract

Insects lack the ability to synthesize sterols de novo which are required as cell membrane inserts and as precursors for steroid hormones Herbivorous insects typically utilize cholesterol as their primary sterol However plants rarely contain cholesterol and herbivorous insects must therefore produce cholesterol by metabolizing plant sterols Previous studies have shown that insects generally display diversity in phytosterol metabolism Despite the biological importance of sterols there has been no investigation of their metabolism in a naturally occurring herbivorous insect community Therefore we determined the neutral sterol profile of Solidago altissima L six taxonomically and ecologically diverse herbivorous insect associates and the fungal symbiont of one herbivore Our results demonstrated that S altissima contained Δ7sterols spinasterol 22dihydrospinasterol avenasterol and 24epifungisterol and that 85 of the sterol pool existed in a conjugated form Despite feeding on a shared host plant we observed significant variation among herbivores in terms of their qualitative tissue sterol profiles and significant variation in the cholesterol content Cholesterol was absent in two dipteran gallformers and present at extremely low levels in a beetle Cholesterol content was highly variable in three hemipteran phloem feeders even species of the same genus showed substantial differences in their cholesterol contents The fungal ectosymbiont of a dipteran gall former contained primarily ergosterol and two ergosterol precursors The larvae and pupae of the symbiotic gallformer lacked phytosterols phytosterol metabolites or cholesterol instead containing an ergosterol metabolite in addition to unmetabolized ergosterol and erogsterol precursors thus demonstrating the crucial role that a fungal symbiont plays in their nutritional ecology These data are discussed in the context of sterol physiology and metabolism in insects and the potential ecological and evolutionary implicationsWe thank Emily Peeden for gall dissection efforts John Stireman aided with plant community characterization at Beaver Creek Wildlife Area Denise Weyer assisted with plant community characterization at Shelby Bottoms Dean Della Penna provided laboratory space and financial support for some of the sterol extraction sterol sample preparation and analysis Chris Dietrich provided information about the host range of A tartarea Two anonymous reviewers provided helpful criticisms This work was supported by a National Science Foundation grant DEB 0614433 awarded to P Abbot and by a CSREES NRIUSDA grant 20073530218185 awarded to ST Behmer and RJ Grebenok

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