Woodbury, Nathan E - Identification, mode of transmission, and functional role of the microbial symbionts of firebrats, T...

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Summer 2013
Degree type: 
Biological Sciences Department
Senior supervisor: 
Gerhard Gries
Thesis title: 
Identification, mode of transmission, and functional role of the microbial symbionts of firebrats, Thermobia domestica (Thysanura: Lepismatidae)
Given Names: 
Nathan E
Firebrats, Thermobia domestica (Packard), giant silverfish, Ctenolepisma longicaudata Escherich, and common silverfish, Lepisma saccharina L. (all Thysanura: Lepismatidae) are ancient and flightless insects that inhabit human dwellings with preference for particular microclimates. All three thysanurans aggregate on substrates that have previously been visited by conspecifics yet they lack any form of long-distance communication to locate conspecifics and prospective mates in suitable shelters. My objectives were to investigate the mechanisms and functions of this aggregation behaviour in firebrats. Aggregation of firebrats is mediated by two symbiotic microorganisms, the bacterium Enterobacter cloacae (Enterobacteriaceae) and the fungus Mycotypha microspora (Mycotyphaceae). Both microorganisms are abundant within firebrat foreguts and feces, and accumulate within firebrat shelters. Firebrats horizontally acquire these symbionts when they contact shelter-debris, and they transmit the symbionts along with feces; there is no transovarial transmission. Mycotypha microspora and E. cloacae were found to be associated with T. domestica, C. longicaudata and L. saccharina from different geographic locations. Mycotypha microspora also induces arrestment behaviour of closely-related T. domestica and C. longicaudata but not of more distantly-related L. saccharrina. Firebrat arrestment is induced by a surface polysaccharide isolated from E. cloacae, D-glucose produced by cellulase enzymes of M. microspora, and by paper enzymatically degraded by M. microspora. The symbionts provide firebrat nymphs with sufficient nutrients to develop through three larval instars even in the absence of other resources, but without a secondary water-source the symbionts cannot sustain firebrat development to adulthood. M. microspora requires hot and humid environments and proliferates only in those microclimates optimal for their host. Firebrats then aggregate wherever their microbial symbiont thrives. This microbe-based gauging of long-term habitat suitability designates rendezvous sites for male and female firebrats, and it ensures firebrats locate conditions that will promote reproduction and offspring survival.
Thermobia domestica, Enterobacter cloacae, Mycotypha microspora, symbiont, symbiosis, Thysanura
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