Robinson, Sarah Jane; (2000) Latitudinal Variation in Drosophila melanogaster. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

There is widespread latitudinal variation in ectotherms. This latitudinal variation is often the result of a combination of the evolutionary genetic and developmental effects of the changing environment. Drosophila melanogaster is an ideal model organism in which to study this variation. Genetic, latitudinal dines have been found in a number of traits of Drosophila melanogaster. Body size, egg size and ovariole number have been found to increase, and development time to decrease with latitude in more than one continent. Parallel latitudinal clines in different continents indicate that natural selection is responsible for this genetic variation. The developmental effects of the environment can act in the same or opposite direction to the evolutionary effects. To further investigate latitudinal variation in D. melanogaster, latitudinal variation in starvation resistance, fat content and larval growth efficiency were studied. Starvation resistance and fat content in South American populations were found not to vary with latitude. Larval growth efficiency was studied in both South American and Australian populations, and larvae originating from high latitude populations were able to convert a fixed amount of food into larger adult body size. In addition, at lower experimental temperatures, larvae originating from both high and low latitudes converted food into larger adult size. An investigation into the genetic basis of the clines in body size in South America and Australia was performed. Chromosome substitution analysis was done to establish whether any of the chromosomes had large effects on body size, and whether these effects differed between the 2 continents. Chromosome 3 was found to have the largest effect on body size in both continents, with the other chromosomes also having some effect.

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