Geography, Host Plants, and Genetic Differentiation
This research examines whether the central Mexican population of the apple maggot fly (Rhagoletis pomonella) differs genetically from the eastern North American population. The Rhagoletis fruit fly is a pest that is a threat to domestic agriculture. In Rhagoletis fruit flies, and many other phytophagous insects, evolution of new species often involves a shift to a new host plant. Because the life history of Rhagoletis fruit flies is closely tied to their host plant, populations on different hosts are reproductively isolated. The prevailing life history pattern in Rhagoletis fruit flies is that species feed on different host plants and occur sympatrically. The exception to this pattern is Mexican Rhagoletis pomonella, which live in the highlands around Mexico City but feed on the same hawthorn host plant as northern R. pomonella. Mexican Rhagoletis pomonella can also shift to new plants. For example, have apparently independently shifted to the apples in Mexico. Preliminary electrophoretic work on the Mexican R. pomonella revealed variation in the gene that codes for the enzyme aldolase, which suggests genetic divergence from other populations of R. pomonella and other closely related Rhagoletis species. In order to study these fruit flies in depth, I amplified and sequenced DNA that codes for the enzyme aldolase from select Mexican populations of R. pomonella. Some samples even required the use of cloning in order to get DNA that would properly sequence. DNA from other Rhagoletis species were used in order to have a complete data set for comparison. Phylogenetic trees will be constructed using the DNA sequences of the Mexican R. pomonella and the other Rhagoletis species in order visualize the degree of divergence of the Mexican R. pomonella. While preparing the DNA to make a phylogenetic tree, anomalies were found that could support the hypothesis of divergence in the Mexican Pomonella. One such anomaly was found in the intron of the aldolase gene. Some species of the R. pomonella species group have aldolase introns of varying lengths. Although the intron does not play a significant role in the functioning of the aldolase gene, these length variations can provide insight on the evolutionary differences in the Rhagoletis species. If the data reveal that there has been a significant amount of divergence, this study will show that Mexican R. pomonella may, in fact be a distinct species, which has independently colonized apples.
School:
University of Illinois at Urbana-Champaign
Department:
Biology Honors / Biochemistry
Research Advisor:
Stewart Berlocher
Department of Research Advisor:
Entomology
Year of Publication:
2002