Alford, Lucy (2010)
Ph.D. thesis, University of Birmingham.
Insects are ectotherms and have limited ability to regulate body temperature above or below ambient and are consequently greatly affected by temperature. The aphid \(Myzus\) \(persicae\) has an extensive distribution throughout Europe from Scandinavia to Southern Spain, representing three distinct climatic regions: sub-Arctic, temperate and Mediterranean. The aphid also has genetically distinct clones within its holocyclic (sexual) and anholocyclic (asexual) life cycles. This raises the possibility that aphids are regionally-adapted to distinct climatic zones along the latitudinal cline of its European distribution. Genetically distinct clones of \(M. persicae\) were collected from Sweden, UK and Spain. Indices of temperature tolerance (upper and lower lethal temperature50, coma temperatures and mobility thresholds) were determined for each aphid clone at different rearing temperatures. Acclimation at 10°C for one generation increased cold tolerance by depressing lower lethal, chill movement and chill coma temperatures when compared to 20°C and 25°C and further enabled mobility to be maintained to lower temperatures. Acclimation at 25°C for one generation increased heat tolerance by raising upper lethal, heat movement and heat coma temperatures when compared to 10°C and 20°C. Acclimation at 10°C also acted to raise upper lethal temperatures, indicating that the physiological processes conferring heat tolerance are induced at both high and low temperatures. Data did not support intergenerational acclimation to higher or lower temperatures. Lower thermal limits were more plastic than upper limits, enabling tolerance ranges to be increased following acclimation at 10°C, but reduced on acclimation at 25°C. Rates of change varied between clones, suggesting that certain clones could be more affected by climate change. A relationship between thermal tolerance range and latitude was not supported by data on thermal traits investigated with the exception of heat coma temperature. This suggests that clonal mixing across Europe is extensive and prevents local adaptation, although long term populations could persist in the Mediterranean allowing increased heat tolerance. Clonal type, as identified by microsatellite analysis, did show a relationship with thermal tolerance, suggesting that clonal types could respond independently to climate change, affecting relative proportions of clones within populations.
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