Thesis (PhD (Botany and Zoology))--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Insect societies utilize advanced chemical communication systems to organize many
aspects of their social life, which among others, include reproduction, thus
maintaining colony homeostasis. The queen pheromone complex (QMP), dominated
by (E)-9-keto-2-decenoic acid (9ODA) is of integral importance in regulating worker
reproductive development. Unique characteristics, associated with reproductive
dominance, enabled the successful establishment of Apis mellifera capensis workers
as social parasites (or pseudoqueens) in colonies of the neighbouring A. m. scutellata.
This suggested that producing a queenlike pheromonal bouquet is one of the
proximate factors in their success.
In this study we attempted to address the pheromone communication dilemma by
investigating whether the phenotypic expression of mandibular gland signals in
honeybee workers are under genetic and/or environmental influence. It was
hypothesized that the mandibular gland profiles of queens and workers may be closely
correlated to specific genotypes in the colony. However, different ageing and rearing
environments (social context) can ultimately influence gene expression with respect to
mandibular gland signals, highlighting the fact that environmental influences are not
necessarily non-significant. In our experiments, both environmental/social conditions
and genotypes of our test individuals were manipulated.
The capensis workers used in our experiment from their native range (Western Cape
area are refered to as native workers, while capensis parasitic workers, from the clonal
parasitic lineage, were obtained from the Gauteng area. A. m. scutellata workers were
obtained from their native range, north of the hybrid zone. Both native and parasitic workers showed the potential to become reproductively
active, but the rapid pheromonal development of parasitic workers placed them at a
reproductive advantage. Parasitic workers started producing low levels of 9HDA, the
precursor to the queen substance 9ODA, between 12-24 hrs, while native workers
only did so after 24 hrs. Despite this, rapid signal development did not culminate in
the parasitic clones always pheromonally out-competing native workers. Withinin
groups of native workers and a single clonal parasitic worker, the mandibular gland
profiles of most workers were dominated by 9ODA and 9HDA (> 80% of extracts)
with only 43% of the single parasitic workers producing higher amounts of 9ODA
than native workers.
Mandibular gland pheromone profiles converged in groups of workers sharing a
greater proportion of genes, providing support for a link to genotypic affects. Workers
that were 75 – 99% related diverged significantly from groups with lower levels of
relatedness was largely due to the presences of 9ODA (Spearman’s rank correlation r
= 0.66, p < 0.0001). Despite the tendency for signal to convergence in groups of
closer relatedness a considerable amount of signal variability was also observed under
varying social conditions. Workers originating from a single capensis queen but aged
under queenright and queenless conditions had very distinct mandibular gland profiles
(Wilks’ lambda λ = 0.118, χ2 = 331.002, p < 0.0001). This variability was thus a
result of the social environment that the workers were exposed to. The physiological
traits, namely mandibular gland pheromone production, linked to reproductive
potential in honeybee workers seem to be determined by a combination of
environmental and genetic factors. Queen mandibular gland pheromone biosynthesis
is genetically predisposed in certain workers however the final oxidation step to
9ODA is strongly influenced by the social environment. The signal plasticity
observed in this study is adaptive and assists workers to realize their reproductive
potential. / AFRIKAANSE OPSOMMING: Insek gemeenskappe gebruik gevorderde chemiese kommunikasie sisteme om
verskeie aspekte van sosiale lewe, onder andere reproduksie, te organiseer en
sodoende word korf homeostasis handhaaf. Die feromoon kompleks van die
koninginby, wat hoofsaaklik uit (E)-9-keto-2-decenoic acid (9ODA) bestaan speel ʼn
belangrike rol in die regulering van reproduksie in heuningby werkers. Die
suksesvolle vestiging van Apis mellifera capensis werkers as sosiale parasiete (pseudo
koninginne) in die korwe van die naburige A. m. scutellata, is bewerkstellig deur hul
unieke kenmerke, wat met reproduktiewe oorheersing verband hou. Dit suggereer dat
die produksie van ʼn tipiese koningin feromoon sein een van verskeie beduidende
faktore is in capensis werkers se sukses.
In hierdie studie het ons die dilemma van feromoon kommunikasie probeer aanspreek
deur te ondersoek of die fenotipiese uitdrukking van seine van die mandibulêre kliere
deur genetiese en/of omgewings faktore beïnvloed word. Die hipotese was dat die
mandibulêre klier profiele van koninginne en werkers korreleer met spesifieke
genotipes in die korf. Die verskillende omgewings waarin werkers groot gemaak word
en verouder (sosiale konteks), kan uiteindelik die uitdrukking van gene, raakende
mandibulêre kliere, beïnvloed. Dit beklemtoon die feit dat omgewings faktore nie
noodwendig onbeduidend is nie. Beide omgewings/sosiale toestande and genotipes
van toets individue is in ons eksperimente gemanipuleer.
Die capensis werkers afkomstig uit hul natuurlike habitat (Weskaap area) wat in ons
eksperimente gebruik is word na verwys as inboorling werkers, terwyl parasitiese
capensis werkers, van klonies parasitiese afkoms, vanuit die Gauteng area verkry is.
A. m. scutellata werkers was vanuit hul natuurlike habitat, noord van die, hybried
sone, verkry.
Beide inboorling en parasitise werkers het die potensiaal getoon om reproduktief
aktief te word, maar versnelde feromoon ontwikkeling van parasite werkers het hulle
ʼn reproduktiewe voordeel gegee. Parasiet werkers het reeds lae hoeveelhede 9HDA,
die voorganger van 9ODA, begin produseer tussen 12 – 24 uur, terwyl inboorling
werkers produksie eers na 24 uur begin het. Ten spyte van die versnelde ontwikkeling
in parasiet werkers het dit nie gelei daartoe dat kloniese parasiete altyd feromonies die
oorhand oor inboorling werkers gekry het nie. In groepe bestaande uit inboorling
werkers en ʼn enkele parasite werker, was die mandibulêre klier profiele altyd deur
9ODA en 9HDA (> 80% van ekstrakte) gedomineer. Slegs 43% van parasite werkers
het groter hoeveelhede 9ODA as inboorling werkers geproduseer.
In groepe werkers, wat ʼn groter proporsie gene in gemeen gehad het, het mandibulêre
klier profiele konvergeer. Dit ondersteun die bestaan van ʼn verband met genotipiese
invloed. Werkers van 75 – 99% verwantskap het beduidend verskil van groepe met
laer verwantskapsvlakke, hoofsaaklik as gevolg van die teenwoordigheid van 9ODA
(Spearman’s rank korrelasie r = 0.66, p < 0.0001). Ten spyte van die konvergerende
neiging van profiele, van meer verwante groepe, was aansienlike veranderlikheid
onder verskillende sosiale toestande waargeneem. Werkers, afkomstig vanaf ʼn enkele
capensis koninginby, maar òf in die teenwoordigheid òf afwesigheid van ʼn koningin
verouder is, het baie kenmerkende mandibulêre klier profiele getoon (Wilks’ lambda
λ = 0.118, χ2 = 331.002, p < 0.0001). Die veranderlikheid was dus ʼn gevolg van
die sosiale omgewing waaraan die werkers blootgestel was. Dit blyk asof die
fisiologiese kenmerke wat met reproduksie potensiaal in heuningbye verband hou,
naamlik mandibulêre klier feromoon produksie, deur ʼn kombinasie van genetiese – en
omgewings faktore beïnvloed word. Sekere werkers is meer geneig tot die biosintese
van koningin mandibulêre klier feromoon as gevolg van hul genetika, terwyl die
finale oksidasie na 9ODA onder sterk omgewings invloed is. Die plastisiteit in
mandibulêre seine waargeneem in hierdie studie, is aanpasbaar en help werkers om
hul reproduksie potensiaal te bereik.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6887 |
| Date | 03 1900 |
| Creators | Noach-Pienaar, Lee-Ann |
| Contributors | Wossler, Theresa C., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 202 p. : ill. |
| Rights | Stellenbosch University |
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