Effects of thermal history on temperature-dependent flight performance in insects : Ceratitis capitata (Diptera: Tephritidae) as a model organism

Esterhuizen, Nanike (2013-12)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Understanding the impact of environmental factors on locomotor performance and flight energetics is of fundamental importance to understanding evolution and ecology. Increased performance that leads to increased dispersal ability can result in increased migration distance to reach optimal habitats, increased gene flow between populations and an overall contribution to the survival of individuals as well as the structuring of species‟ geographic range sizes. The temperature-dependent nature of insects, in conjunction with predicted climate change and shifting optimal climatic ranges, could have important ecological and economic consequences such as increased invasion by alien and pest species. In this study, the influence of thermal history on temperature-dependent flight performance was investigated in a notorious invasive agricultural pest, Ceratitis capitata (Diptera: Tephritidae). Flies were exposed to one of four developmental acclimation temperatures (Tacc: 15, 20, 25, 30°C) during their pupal stage and tested at random at either of those temperatures (Ttest) as adults in a full-factorial experimental design. Major factors influencing flight performance included sex, body mass, Ttest and the interaction between Ttest and Tacc. Performance increased with increasing Ttest across all acclimation groups, e.g. at 15°C only 10% of all flies had successful flight, whereas at 30°C the success rate was 76.5%. Even though Tacc alone did not affect flight performance, it did have an effect in combination with Ttest. The negative interaction term Ttest x Tacc, in combination with a multiple comparison between Tacc groups at each Ttest, indicated that flies acclimated to 15°C and 20°C performed better than those acclimated to 25°C and 30°C when tested at cold temperatures. This provides partial support for the "colder is better‟ hypothesis. To explain these results, several key, flight-related traits were examined to determine if Tacc influenced flight performance as a consequence of changes in body or wing morphology, whole-animal metabolic rate or cytochrome c oxidase (CCO) activity. Although significant effects of Tacc could be detected in several of the traits examined, with emphasis on sex-related differences, increased flight performance could not be explained solely on the basis of changes in any one of these traits. To illustrate the potential applied value of this study, the main flight performance outcomes were also coupled with a degree-day (thermal development) model to determine if knowledge of flight ability could improve predicted population dynamics. The results and insights obtained from this study are broadly applicable to a variety of insect species and demonstrate that, by recognising the impact of environmental factors on locomotor performance and flight energetics, an increased understanding of the functioning, biology and evolution of flight-capable arthropods can be obtained.

AFRIKAANSE OPSOMMING: Groter begrip van die impak van omgewingsfaktore op bewegingsprestasie en vlug-energetika is van fundamentele belang vir die verstaan van evolusie en ekologie. Verhoogde bewegingsprestasie wat lei tot verbeterde verspreidingsvermoë kan 'n toename in migrasieafstand om optimale habitat te bereik, verhoogde genevloei tussen populasies en ʼn algehele bydrae tot die oorlewing van individue sowel as die strukturering van spesies se geografiese gebiedsgroottes tot gevolg hê. Die temperatuurafhanklike aard van insekte, tesame met voorspelde klimaatsverandering en die verskuiwing van optimale klimaatsones, kan belangrike ekologiese en ekonomiese gevolge, soos verhoogde indringing deur uitheemse en pes-spesies, inhou. Die invloed van termiese geskiedenis op die temperatuurafhanklike vlugprestasie van 'n berugte indringer-landboupes, Ceratitis capitata (Diptera: Tephritidae), word in hierdie studie ondersoek. Vlieë is blootgestel aan een van vier akklimasie-temperature (Tacc: 15, 20, 25, 30°C) tydens hul papiestadium en is op ewekansige wyse in 'n vol-faktoriale eksperimentele ontwerp by een van dieselfde toetstemperature (Ttest) as volwassenes getoets. Belangrike faktore wat vlugprestasie beïnvloed het, sluit geslag, liggaamsmassa, Ttest en die interaksie tussen Ttest en Tacc in. Prestasie het verbeter met toenemende Ttest oor al die akklimasiegroepe, bv. by 15°C het net 10% van alle vlieë suksesvol gevlieg, terwyl die sukseskoers by 30°C, 76,5% was. Selfs al het Tacc alleen nie die vlugprestasie beïnvloed nie, het dit 'n effek in kombinasie met Ttest gehad. Die negatiewe interaksie term Ttest x Tacc, in samewerking met 'n meervoudige vergelyking tussen Tacc groepe by elke Ttest, het aangedui dat vlieë wat by 15°C en 20°C geakkimeer was, beter presteer het as dié wat by 25°C en 30°C geakklimeer was wanneer hulle by koue temperature getoets was. Dit bied gedeeltelike ondersteuning vir die "kouer is beter" hipotese. Om hierdie resultate te verklaar, is 'n paar sleutel vlugverwante eienskappe ondersoek om te bepaal of Tacc vlugprestasie a.g.v. veranderinge in die liggaam- of vlerkmorfologie, die hele-dier metaboliesetempo of sitochroom-c oksidase (CCO) aktiwiteit beïnvloed. Alhoewel beduidende effekte van Tacc op verskeie van hierdie eienskappe, veral wat geslagsverwante verskille betref, opgemerk is, kan verhoogde vlugprestasie nie uitsluitlik op grond van veranderinge in enige een van die eienskappe verduidelik word nie. Om die potensiële toepassingswaarde van hierdie studie te illustreer, is die hoof vlugprestasie uitkomste gekoppel aan 'n “degree-day” (termiese ontwikkeling)-model om te bepaal of kennis van vlugvermoë voorspellings van bevolkingsdinamika kan verbeter. Hierdie studie se resultate en insigte is oor die algemeen van toepassing op 'n verskeidenheid insek-spesies en toon dat erkenning van die invloed van omgewingsfaktore op bewegingsprestasie en vlug-energetika kan lei tot groter begrip van die funksionering, biologie en evolusie van geleedpotiges.

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