Abstract
The present paper reviews the biology of reed beetles (Donaciinae), presents experimental data on the role of specific symbiotic bacteria, and describes a molecular method for the detection of those bacteria. Reed beetles are herbivores living on wetland plants, each species being mono- or oligo-phagous. They lay their eggs on the host plant and the larvae live underwater in the sediment attached to its roots. The larvae pupate there in a water-tight cocoon, which they build using a secretion that is produced by symbiotic bacteria. The bacteria are located in four blind sacs at the foregut of the larvae; in (female) adults they colonize two out of the six Malpighian tubules. Tetracycline treatment of larvae reduced their pupation rate, although the bacteria could not be fully eliminated. When the small amount of bacterial mass attached to eggs was experimentally removed before hatching, symbiont free larvae resulted, showing the external transmission of the bacteria to the offspring. Specific primers were designed to detect the bacteria, and to confirm their absence in manipulated larvae. The pupation underwater enabled the reed beetles to permanently colonize the wetlands and to diversify in this habitat underexploited by herbivorous insects (adaptive radiation).
Highlights
Symbioses are common in the living world [1,2,3,4,5]
Even if we confine this initial overview to insects and their bacterial endosymbionts, we still find a great number of systems [9,10,11], much of the research has so far concentrated on few classical examples
Direct evidence for the central role the bacteria play for cocoon formation comes from the experiment with tetracycline treated larvae
Summary
Symbioses are common in the living world [1,2,3,4,5]. In addition to macroscopically evident symbioses (like of crabs and anthozoans, [6]), ongoing research reveals more and more examples of predominantly mutualistic relationships, in which plants and animals live together with microorganisms. Fungi and other eukaryotic protists can be involved as symbionts [7,8], which live either in close association with or within their respective host. The benefit to the host is usually assumed to be nutritional Such symbioses can be found in insects that live on a restricted diet deficient in one or more type(s) of nutrients [12,13,14,15]. The evolutionary innovation achieved is usually the exploitation of a new food source Concentration on these systems may have caused a bias in the spectrum of interactions, the low number of interactions other than mutual exchange of nutrients seems to be real. We established and describe a molecular method for the detection of the symbionts applicable to early instar larvae, which is at the same time a proof of the transmission pathway
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