Species-specific hydrocarbon profiles of South African fig wasp communities (Hymenoptera : Chalcidoidea)

Van der Merwe, Julia Frances (2012-03)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Cuticular hydrocarbon (CHC) profiles of insects play roles in behavioural interactions within and between species, encompassing species-, colony- and mate-recognition. CHCs are largely genetically determined and are thus unique to each species, making them useful in chemotaxonomy. However, species exhibit intra-species variation in their CHC profile which can be the result of both intra-species genetic variation as well as environmental influences such as habitat effects, colony effects, diet, host switching, as well as adsorption of CHCs from other insects. Studies have found that the CHC profiles of a specific insect species will often exhibit variations between regions as well as the species of host the insect is associated with. Therefore, an ideal system to investigate the effects of genetic population structure and environment on the CHC profiles of insects is within the fig – fig wasp mutualism. Fig species occur in a wide variety of habitats and host a diverse complement of fig wasp species. We were therefore offered the opportunity to investigate a wide range of potential influences on fig wasp CHC profiles ranging from environmental to genetic effects. Firstly, through GC-MS we found that the CHC profiles of the fig wasps investigated are both species-specific and species-group-specific, with the species Elisabethiella glumosae, Elisabethiella stuckenbergi and Ceratosolen capensis, and two Otitesella species-groups (the Uluzi and Sesqui species-groups) separating out significantly. Consensus phylogenies (based on COI, Cytb and EF-1α) showed that within the galling fig wasp genus Otitesella there were multiple genetic lineages within a species-group which corresponds to species-level genetic variation, and that each genetic lineage was confined to a single host fig species. The CHC profiles reflected the genetic relationships between the two species-groups, and the CHC profiles within a species group could be differentiated by genetic lineage/host species. This indicated that although genetic lineage was mostly responsible for the observed variation in CHC profiles, factors associated with different host species also had an effect. Strong regional variation overriding both the influence of genetic lineage and factors associated with host species were observed in the CHC profiles of the fig wasps within a species-group. This regional variation in CHC profiles was also observed within two pollinating fig wasp species, Elisabethiella stuckenbergi and Ceratosolen capensis, which was not supported by population genetic data (COI and Cytb). In fact, very little genetic population structure was found within the pollinating species, even though the pollinators were collected across South Africa. The lack of genetic structure in pollinating fig wasps can be the result of high gene flow caused by the large dispersal capability of pollinating fig wasps. Our results indicated that fig wasp CHC profiles have the potential to be used in chemotaxonomy and are possibly used as species and mate-recognition cues by the fig wasps. Furthermore, we found both a regional and associated host species effect on the CHC profile. We suggest that the observed regional effect in this study could be attributed to habitat differences and differences in fig wasp community between regions. Moreover, the effect host species had on the CHC profiles may be as a result of dietary differences between galls in different host species. A possible consequence of the observed regional/host speciesassociated effect on fig wasp CHC profiles is that it could lead to pre-mating isolation within fig wasp species, which could ultimately result in speciation. In addition, our results indicated that the interpretation of the variation in the fig wasp CHC profile was dependent on the scale of the analysis: on a broad, inter-species-level scale, fig wasp CHC profiles were species-specific; on a finer intra-species scale, variation in CHC profiles occurred between fig wasps collected from different regions; and on a within-region scale, variation in CHC profiles within species-groups occurred between genetic lineages/host species. Future studies should look at the application of CHCs in chemotaxonomic studies on the fig wasp phylogeny, as well as the effect of fig wasp community composition on fig wasp CHCs.

AFRIKAANSE OPSOMMING: Kutikulêre koolwaterstof (KK) profiele van insekte speel rolle in die gedragsinteraksies binne sowel as tussen spesies, en behels die herkenning van spesieof kolonielidmaatskap asook potensiële maats. Kutikulêre koolwaterstowwe word meestal deur gene bepaal en is dus uniek vir elke spesie, wat dit handig maak vir chemotaksonomie. Spesies vertoon egter soms intraspesie variasie in hul KK profiele wat die gevolg kan wees van beide intraspesie genetiese variasie sowel as omgewingsinvloede soos habitat effekte, kolonie effekte, dieet, tussen-gasheer skuiwings, asook die adsorpsie van ander insekte se kutikulêre koolwaterstowwe. Studies het gevind dat die kutikulêre koolwaterstof profiele van ʼn spesifieke insek spesie op ʼn gereelde basis verskille vertoon tussen streke asook tussen die verskillende gasheer spesies waarmee die insek geassosieer is. Om hierdie redes is die vy – vy-wesp mutualisme ʼn ideale sisteem om die uitwerking van genetiese populasie struktuur en omgewing op die KK profiele van insekte te ondersoek. Vy spesies kom in ʼn wye verskeidenheid van habitatte voor en ondersteun ʼn diverse groep vy-wesp spesies. Dit het ons die geleentheid gebied om ʼn wye reeks moontlike invloede van vy-wesp KK profiele te ondersoek, van omgewings- tot genetiese invloede. Eerstens, deur die gebruik van GC-MS het ons gevind dat die KK profiele van die vy-wespe wat ondersoek was beide spesie-spesifiek en spesie-groep-spesifiek is, met die spesies Elisabethiella glumosae, Elisabethiella stuckenbergi en Ceratosolen capensis, asook twee Otitesella spesie-groepe (die Uluzi en Sesqui spesie-groepe) wat betekenisvol onderskei kon word. Konsensus filogenieë (gegrond op COI, Cytb en EF1-1α) het getoon dat daar in die gal-induserende vy-wesp genus Otitesella veelvuldige genetiese lyne binne die spesie-groepe voorgekom het ooreenstemmend met tussen-spesie genetiese variasie, en dat elke genetiese lyn beperk was tot ʼn enkele gasheer vy spesie. Die KK profiele het die genetiese verhoudings tussen die twee spesie-groepe weerspieël, en die KK profiele binne ʼn spesie-groep kon onderskei word op grond van hul genetiese lyn/gasheer spesie. Hierdie het getoon dat, alhoewel genetiese lyn meestal verantwoordelik was vir die waargeneemde variasie in KK profiele, faktore wat met verskille in gasheer spesies gepaard gaan ook ʼn effek gehad het. Sterk streeks-verbonde variasie wat beide die invloed van genetiese lyn, én faktore wat met verskille in gasheer spesie gepaard gaan, oortref het, was waargeneem in die KK profiele van die vy-wespe binne ʼn spesie-groep. Hierdie streeks-verbonde variasie in KK profiele was ook waargeneem in twee bestuiwende vy-wespe, Elisabethiella stuckenbergi en Ceratosolen capensis, ʼn resultaat wat nie ondersteun was deur die genetiese bevolkingsdata nie (COI en Cytb). In werklikheid was baie min genetiese bevolkings-struktuur opgespoor binne die bestuiwer spesies, selfs as was die bestuiwer spesies regoor Suid-Afrika ingesamel. Die tekort aan genetiese struktuur in die vy-wesp bestuiwers kan die gevolg wees van hoë geenvloei wat veroorsaak word deur die hoë verspreidingskapasiteit van bestuiwende vy-wespe. Die resultate toon aan dat vy-wesp KK profiele die potensiaal besit om in chemotaksonomie gebruik te word, en word moontlik deur vy-wespe gebruik as kenmerke vir die herkenning van spesie en potensiële maats. Verder was daar gevind dat daar beide ʼn streekseffek en ʼn effek geassosieer met gasheer spesie op KK profiele was. Ons stel voor dat die waargeneemde streekseffek in hierdie studie toegeskryf kan word aan verskille tussen habitatte asook streeksverbonde verskille tussen vy-wesp gemeenskappe. Boonop kan die effek wat gasheer spesie op die KK profiele gehad het ʼn gevolg wees van dieetverskille tussen die galle in verskillende gasheer spesies. ʼn Moontlike gevolg van die waargeneemde streeks/gasheer-spesie-geassosieerde effek op vy-wesp KK profiele is dat dit moontlik kon lei tot voor-paring-isolasie binne vy-wesp spesies, wat uiteindelik spesiasie kon veroorsaak het. Daarbenewens wys ons resultate dat die interpretasie van die variasie in die vy-wesp KK profiel was afhanklik van die skaal van die analise: op ʼn breë interspesie vlak was die vy-wesp KK profiele spesiespesifiek; op ʼn fyner intra-spesie vlak het variasie in KK profiele voorgekom tussen vy-wespe wat in verskillende streke ingesamel was; en op streeksvlak het variasie in die KK profiele binne spesie-groepe voorgekom tussen genetiese lyne/gasheer spesies. Toekomstige studies behoort te kyk na die toepassing van kutikulêre koolwaterstowwe in chemotaksonomiese studies van die vy-wesp filogenie, asook die effek wat vy-wesp gemeenskap samestelling het op vy-wesp kutikulêre koolwaterstowwe.

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