| Summary: | Thesis (MScAgric (Conservation Ecology and Entomology))--Stellenbosch University, 2011 === ENGLISH ABSTRACT: Climate change will alter both temperature and moisture availability in the future and therefore will
likely affect vector borne disease prevalence. Organisms faced with changes in weather can respond
in a variety of ways and this complicates any predictions and inferences for these organisms with
climate change. Cause-and-effect links between climate change, insect vector responses, and
changes in risk of disease transmission are poorly established for most vector borne diseases. Tsetse
(Diptera, Glossinidae) are important vectors of trypanosome parasites posing a major threat to
human health and socio-economic welfare in Africa. Water balance plays an important role in
determining activity patterns, energy budgets, survival and population dynamics and, hence,
geographic distribution and abundance of insects. Glossina species occupy a wide range of habitats
in Africa and are notable for their desiccation resistance in xeric environments. Yet, whether or not
the different species, subgroups or ecotype groups differ in susceptibility to changes in weather
remain undetermined.
The first main focus of my thesis was to test the effects of climate change on water balance traits
(water loss rate, body water content and body lipid content) of adult tsetse flies. Four species from
xeric and mesic habitats were exposed to a range of temperature (20 – 30 °C) and relative humidity
(0 – 99 %) combinations. Water loss rates were significantly affected by measurement treatments,
while body water content, body lipid content and mass were less affected and less variable across
treatment combinations. The results provide support for mass-independent inter- and intra-specific
variation in water loss rate and survival times. Therefore, water balance responses to variation in
temperature and relative humidity are complex in Glossina, and this response varies within and
among species, sub-groups and ecotypes in terms of magnitude and the direction of effect change.
Secondly, I apply a mechanistic distribution model for G. pallidipes to predict potential population
responses to climate change. I validate the mechanistic model (NicheMapperTM) results spatially
and temporally using two methods. Both tests of the model showed that NicheMapper‟s predicted
resting metabolic rate has great potential to capture various aspects of population dynamics and
biogeography in G. pallidipes. Furthermore, I simulate the effect of phenotypic plasticity under
different climate change scenarios and solve for the basic reproductive number of the
trypanosomiasis disease (R0) under a future climate scenario.
This integrated thesis provides strong evidence for a general decrease in optimal habitat for G.
pallidipes under future climate change scenarios. However, it also provides strong support for a 1.85 fold increase in R0 based on changes in biting frequency as a result of higher predicted
metabolic rates in the future. This might suggest that the reduction in optimal habitat could be
outweighed by the increase in R0. The results demonstrate that an understanding of the
physiological mechanism(s) influencing vectors of disease with climate change can provide insight
into forecasting variation in vector abundance and disease risk. === AFRIKAANSE OPSOMMING: Die invloed van klimaatsverandering op die temperatuur en vog beskikbaarheid mag moontlik
insek-oordraagbare siektes in the toekoms beïnvloed. Organismes wat verandering in klimaat ervaar
kan op verskillende maniere reageer en daarom is voorspelling en afleidings van die reaksies op
klimaatsverandering nie eenvoudig nie. Boonop is die verband tussen klimaatsverandering, insek
reaksies en veranderinge in die oordragsrisiko van siektes onbekend vir die meeste insekoordraagbare
siektes. Tsetse (Diptera: Glossinidae) is belangrike draers van trypanosoom parasiete
wat 'n bedreiging inhou vir mensegesondheid en sosio-ekonomiese welsyn in Afrika. Waterbalans
speel 'n belangrike rol in die energiebondel samestelling, aktiwiteitspatrone, oorlewing en populasie
dinamika van insekte en, dus, die geografiese voorkoms en verspreiding van insekte. Glossina
spesies kom in 'n verskeidenheid habitatte in Afrika voor en is bekend daarvoor dat hulle weerstand
bied teen uitdroging in droё habitatte. Maar, die mate waartoe die verskillende subgroepe,
ekotiepegroepe en spesies kwesbaar is vir klimaatsverandering, is steeds onbekend.
Die eerste hooffokus van my tesis was om die uitwerking van klimaatsverandering op waterbalansrelevante
uitkomste (tempo van waterverlies, waterinhoud en vetinhoud) van volwasse tsetse vlieё
te bestudeer. Vier spesies van droë en klam habitatte is aan verskillende kombinasies van
temperatuur (20 – 30 °C) en relatiewe humiditeit (0 – 99 %) blootgestel. Die tempo van
waterverlies is betekenisvol deur die verskillende toetskombinasies beïnvloed, terwyl die waterinhoud,
vetinhoud en liggaamsmassa tot 'n minder mate beïnvloed is en minder gevarieer het tussen
die toetskombinasies. Die resultate toon bewyse vir gewigs-onafhanklike inter- en intraspesie
variasie in waterverlies tempo‟s en oorlewingstyd. Die waterbalans uitkomste op variasie in
temperatuur en relatiewe humiditeit is dus ingewikkeld in Glossina, en dit varieer binne en tussen
spesies, subgroepe en ekotiepe in terme van die graad en rigting van effek verandering.
Tweedens pas ek 'n meganistiese verspreidingsmodel toe vir G. pallidipes om die moontlike
populasiereaksies met klimaatsverandering te voorspel. Ek toets die antwoorde van die model
(NicheMapperTM) oor tyd en skaal op twee verskillende maniere. Beide toetse het aangedui dat die
NicheMapper voorspelde rustende metaboliese tempo die verskillende aspekte van G. pallidipes
populasie dinamika en biogeografie goed beskryf. Ek simuleer die uitkomste van die fenotipiese
veranderbaarheid van G. pallidipes onder „n verskeidenheid klimaatsverandering-uitkomste, en los „n model van die basiese ommekeer van trypanosomiasis (R0) op onder 'n klimatsverandering
situasie in die toekoms.
Hierdie geïntegreerde tesis toon sterk bewyse dat die optimale habitat van G. pallidipes verminder
met klimaatsverandering. Dit toon egter ook bewyse vir 'n 1.85 keer toename in R0 gebasseer op 'n
verhoging in die frekwensie van bytgeleenthede weens die hoër voorspelde metaboliese tempo van
die vlieë in die toekoms. Laasgenoemde stel voor dat die afname in optimale habitat moontlik deur
'n toename in R0 oorheers sal word. Die resultate demonstreer dat beter begrip van die fisiologiese
meganisme(s) wat parasiet-draers beïnvloed verdere insig kan voorsien in die toekomstige
voorspelling van draer teenwoordigheid en siekte waarskynlikheid.
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