No evidence of metabolic cold adaptation in Drosophila melanogaster along a latitudinal gradient in Australia

O'Toole, Sinead (2018-03)

Thesis (MScConsEcol)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: Metabolic cold adaptation (MCA) is a controversial hypothesis that suggests cold-adapted species should have a higher resting metabolic rate (RMR), or an altered metabolic rate- temperature (MR-T) relationship when compared to their warmer counterparts at the same test temperature. This intraspecific study provides a novel experimental assessment testing MCA in four populations of Drosophila melanogaster found across a latitudinal cline of eastern Australia. Specifically, I test the prediction that the higher latitude populations (from colder environmental temperatures) show an elevated RMR or a lower/higher activation energy (𝐸𝑎) which might reflect a change in MR-T sensitivity. Populations were reared in the laboratory under common conditions before being acclimated for 5 days to stable 18°C and 25°C, as well as fluctuating temperatures of 13-22°C and 20-30°C to test if MR was affected by acclimation. MR was estimated at 6 test temperatures (10°C, 15°C, 20°C, 25°C 30°C and 35°C). After adjusting for mass and activity, no population was found to have a consistently higher RMR at any acclimation condition. Acclimation to stable 25°C resulted in slightly lower 𝐸𝑎 for two populations, but decreasing 𝐸𝑎 did not correlate with increasing latitude. No other differences in 𝐸𝑎 were found. The study concludes there is no evidence of MCA among populations of D. melanogaster in Australia- possibly due to the lack of consistently cold temperatures in some higher latitudes of the Southern Hemisphere that would perhaps be likely to drive such an adaptation.

AFRIKAANSE OPSOMMING: Spesies aangepas vir koue temperature moet volgens die kontroversiële Metaboliese koue aanpassings hipotese ʼn hoër rustende metaboliese tempo of 'n gewysigde metaboliese tempo-temperatuur verhouding hê in vergelyking met hul gematigde eweknieë. Hierdie intra-spesifieke studie verskaf ʼn nuwe eksperimentele assessering wat die Metaboliese koue aanpassings-hipotese toets in vier Drosophila melanogaster bevolkings, versprei oor verskeie breedtegrade van oostelike Australië. Hier toets ek spesifiek die voorspelling dat bevolkings van hoër breedtegrade (kouer omgewingstemperature) ʼn verhoogde rustende metaboliese tempo of 'n laer aktiveringsenergie sal toon, wat 'n verandering in die metaboliese tempo temperatuur verhouding se sensitiwiteit kan weerspieël. Om te bepaal of akklimatisering ʼn invloed op die metaboliese tempo van die bevolkings het, is die verskillende bevolkings in die laboratorium onder algemene toestande grootgemaak waarna hulle vir 5 dae by ʼn stabiele 18°C en 25°C geakklimatiseer is, asook by fluktuerende temperature van 13-22°C en 20-30°C. Metaboliese tempo is bepaal by 6 verskillende toetstemperature (10°C, 15°C, 20°C, 25°C 30°C en 35°C). Nadat beide massa en aktiwiteit in ag geneem is, was daar geen bevolking wat konsekwent ʼn hoër rustende metaboliese tempo by enige van die akklimatiserings -temperature getoon het nie. In twee populasies, is ʼn effens laer aktiveringsenergie verkry by 25°C stabiele akklimatisering, maar die dalende aktiveringsenergie het nie met ʼn toename in breedtegraad verband gehou nie. Geen ander verskille in aktiveringsenergie is waargeneem nie. Hierdie studie kom dus tot die gevolgtrekking dat daar geen bewys van die Metaboliese koue aanpassings-hipotese onder bevolkings van D. melanogaster in Australië is nie. Dit kan moontlik toegeskryf word aan die gebrek aan konsekwente koue temperature in die hoër breedtegrade van die Suidelike Halfrond wat moontlik so 'n aanpassing sou kon aanvoer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/103830
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