2020-12-31 Thermal biology of the invasive ladybird Harmonia axyridis : physiological plasticity, thermoregulatory behaviour and fitness

Shinner, Rebecca (2014-12)

Thesis (MSc)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Physiological and behavioural responses to changes in temperature may enable ectotherms to buffer the effects of climate change or facilitate movement into novel environments. The thermal biology of the harlequin ladybird Harmonia axyridis is of considerable interest since it is a globally invasive species and threatens native aphidophagous coccinellids. Here, laboratory experiments were used to assess the effects of thermal acclimation (rearing temperature) on the thermal performance curve for walking speed, and to test the assumptions of the cost benefit model of thermoregulation, while also examining subsequent fitness consequences. Results showed that exposure to temperature treatments either during larval development or adulthood significantly affected thermal preference, thermal tolerance and locomotion in adult H. axyridis. The responses varied between the traits measured and the life stage during which exposure occurred, in some cases reflecting complex trade-offs. Thermal preference was affected by thermal acclimation during adulthood, and was 15 - 20°C lower than the optimum temperature for walking speed in all treatment groups. Critical thermal maximum (upper activity limit) was strongly affected by exposures to temperature treatments as adults, but critical thermal minimum did not vary. Using thermal arenas in which thermal quality was artificially manipulated (high quality vs. low quality environment), the movement of individual H. axyridis females was tracked over a five-day period, after which fecundity was scored. H. axyridis spent longer periods travelling and moved further in the low quality arenas compared to the high quality arenas but maintained body temperatures further from the preferred temperature in the low quality arenas; no significant fitness consequences were observed in terms of fecundity in either arena type. Combined, these findings suggest that H. axyridis uses both thermal acclimation and thermoregulation to readily adjust to changing conditions, which may contribute to its invasiveness. These responses should be accounted for when assessing the ecological impacts of climate change on invasive species.

AFRIKAANSE OPSOMMING: Fisiologiese en gedragsreaksies op veranderinge in die temperatuur kan ektotermiese diere in staat stel om die uitwerking van klimaatsverandering te buffer of beweging na nuwe omgewings te fasiliteer. Die termiese biologie van die harlekyn lieweheersbesie Harmonia axyridis is van groot belang, aangesien dit 'n wêreldwye indringerspesie is en inheemse plantluis-etende Coccinellidae bedreig. Hier is laboratorium eksperimente gebruik om die gevolge van termiese akklimasie (grootmaak temperatuur) op die termiese prestasie kurwe vir stapspoed te bepaal, asook om die aannames van die koste voordeel model van termoregulering te toets, terwyl dit ook die daaropvolgende fiksheidsgevolge ondersoek. Resultate het getoon dat blootstelling aan temperatuur behandelings, hetsy tydens larwe ontwikkeling of volwassenheid, ‘n aansienlike invloed het op temperatuur voorkeur, temperatuur verdraagsaamheid en beweging in volwasse H. axyridis. Die reaksies het gewissel tussen die eienskappe wat gemeet is en die lewenstadium waartydens blootstelling plaasgevind het, in sommige gevalle weerspieël dit komplekse wisselwerkinge. Termiese voorkeur is deur temperatuur akklimasie beïnvloed tydens volwassenheid en was 15-20°C laer as die optimum temperatuur vir stapspoed in al die behandelingsgroepe. Kritiese termiese maksimum (boonste aktiwiteit limiet) is sterk beïnvloed deur die blootstelling aan temperatuur behandelings as volwassenes, maar kritiese termiese minimum het nie gevarieer nie. Deur die gebruik van termiese arenas waarin die temperatuur gehalte kunsmatig gemanipuleer is (hoë gehalte teen lae gehalte omgewing), is die beweging van individuele H. axyridis wyfies gevolg oor 'n vyf-dag-tydperk, waarna vrugbaarheid bepaal is. In vergelyking met die hoë gehalte arenas, spandeer H. axyridis langer tydperke in beweging en het verder beweeg in die lae gehalte arenas, maar het liggamstemperature gehandhaaf verder van die voorkeurtemperatuur in die lae gehalte arenas; geen beduidende fiksheidsgevolge in terme van vrugbaarheid is waargeneem in beide arena tipes nie. Gekombineerd dui hierdie bevindings daarop dat H. axyridis beide termiese akklimasie en termoregulering gebruik om geredelik aan te pas by veranderende omstandighede, wat kan bydra tot sy indringingsvermoë. Hierdie reaksies moet in ag geneem word wanneer die ekologiese impak van klimaatsverandering op indringerspesies bepaal word.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/95778
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