How do honey bees handle their stress? A focus on their gut microbiota and immune system. (Apis mellifera subsp. capensis)

Lawson, Kayla (2018-12)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Gut microbial symbionts have recently been shown to play roles in ensuring overall host health, a hot topic in honey bee research. Honey bees harbour a stable, core bacterial community in the gut, suggested to play a role in host health homeostasis, metabolic functioning, immune regulation, and food degradation. This gut microbiota provides a unique opportunity to observe the effects of common stressors on honey bees. Extrapolating the relationship of host-gut microbiota and immune system from higher hosts, we examined the effects of two common honey bee stressors; the indirect fungicide contamination and nutrient limitation. Honey bee colonies were exposed to the fungicide chlorothalonil and limited to only a single pollen food source, respectively. Effects of these treatments were observed through shifts in their gut microbiota using Automated Ribosomal Intergenic Spacer Analysis (ARISA). The immune response of honey bees was examined through gene expression levels of three immune genes, namely; immune deficiency (imd), prophenoloxidase (proPO), and spaetzle. The longevity of the honey bees was monitored through expression levels of vitellogenin (Vg). Overall colony metadata was also taken to observe changes in colony productivity. Both treatment groups were compared to an untouched, negative control group and a positive control group infected with Paenibacillus larvae. Both the fungicide and nutrient limited treatments showed no significant effect on the hindgut microbial communities but showed significant effects on the midgut communities. These treatments caused downregulation in the energy expensive Imd pathway, vital in the production of Anti-Microbial Peptides (AMPs), an invaluable defence against microbial pathogens. The phenoloxidase pathway was upregulated, ensuring a higher activity of the encapsulation and melanisation process, perhaps to compensate for the observed reduction in activity in the other immune pathways. Both treatments showed no significant effect on the gut-immune communicating Toll-like pathway. Honey bees within the nutrient limited group showed reduced colony productivity, probably as a result of delayed foraging, observed using Vg expression levels. Overall the treatments tested in this study significantly reduced the immune system of honey bees, opening the colonies up to potential secondary infections. This study does not provide any reason to discontinue the current beekeeping practices tested here, but attention should be paid to prevent the possibility of infection of colonies under similar conditions as a result of reduced immune system.

AFRIKAANSE OPSOMMING: Inwendige mikrobiese simbionte speel ‘n belangrike rol om die algemene gesondheid van die gasheer te verseker en hierdie is tans ‘n belangrike onderwerp in heuningbynavorsing. Heuningbye huisves a stabiele en kern bakteriese gemeenskap in die ingewande. Hierdie bakterieë speel moontlik ‘n rol in die gasheer se homeostase, metaboliese funksionering, immuunregulasie en voedselverwerking. Hierdie inwendige mikrobiota voorsien a unieke geleentheid om die effek van algemene stresse op heuningbye waar te neem. Om die verhouding tussen die gasheer en inwendige mikrobiota en die immuunsisteem van hoër gashere te ekstrapoleer, word daar gekyk na die effek van twee algemene heuningby-stressors: die indirekte kontaminasie van swamdoders en die beperking van nutriënte. Heuningby-kolonies was blootgestel aan óf ‘n swamdoder óf ‘n enkele bron van stuifmeel as ‘n voedselbron. Deur die gebruik van Outomatiese Ribosomale Intergeniese Afstand Analiese (ARISA), was die effek van die behandelings waargeneem deur die verskuiwing in die inwendige mikrobiota. Die immuunreaksie van die heuningbye was waargeneem deur die vlakke van geenuitdrukkings van drie verskillende immuungene: Immuun tekort (Imd), profenoloksidase (proPO) en “Spaetzle” (Spz). Die lewensverwagting van die heuningbye was gemonitor deur die uitdrukkingsvlak van “Vitellogenin” (Vg) te meet. Oor die algemeen was die kolonie se metadata ook opgeneem om die verskil in kolonie-produktiwiteit waar te neem. Albei behandelingsgroepe was vergelyk met ‘n onaangeraakte negatiewe kontrole groep, asook ‘n positiewe kontrole groep wat geïnfekteer was met Paenibacillus larvae. Albei die swamdoder en nutriënt-beperkte groepe het geen beduidende effek op die agsterste ingewande gehad nie, maar daar was wel ‘n beduidende effek op die middelste ingewande. Hierdie behandelinge het ‘n afname in die energie-ryke Imd padweg veroorsaak. Hierdie padweg is noodsaaklik in die produksie van AMP’s, ‘n waardevolle verdedigingsmeganisme teen mikrobiese patogene. Die fenoloksidase padweg het toegeneem wat die hoër aktiwiteit van inkapseling en melanisasie verseker. Hierdie is moontlik om te kompenseer vir die afname in die Imd padweg. Albei behandelings het geen beduidende effek op die “Tolllike” padweg gehad nie. Hierdie padweg is die kommunikasie tussen die ingewande en die immuniteit. Heuningbye in die nutriënt-beperkte groep het ‘n afname in kolonie-produktiwiteit getoon. Hierdie kan moontlik wees as gevolg van ‘n vertraagde soek vir kos, wat waargeneem is duer die Vg uitdrukkingsvlakke. Oor die algemeen het die behandelings in hierdie studie die immuunsisteem in heuningbye aansienlik laat val, wat die kolonie dan blootstel aan moontlike sekondêre infeksies. Hierdie studie voorsien geen rede hoekom die huidige byeboerdery gebruike gestaak moet word nie, maar aandag moet gegee word aan die voorkoming van moontlike infeksie van kolonies onder soortgelyke kondisies as gevolg van die onderdrukte immuunsisteem.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105200
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