Owczarzak,+Laura+Physics+Discussion

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Owczarzak,+Laura+Physics+Discussion
Laura Owczarzak
Discussion
Physics 202L
3/21/15
1. The abstract of the paper met Dr. Selkowitz’s criteria. A quick overview of the
paper was given, regarding differentiating accurately between the harmful R. pomonella
and the benign R. zephyria, through the analysis of surstylus in male flies and aculeus in
female flies. A quick conclusion to the study was also given in the abstract, as per Dr.
Selkowitz’s instructions for formal reports. Further investigation into the size and
morphology of these two structures offered better identification of the harmful R.
pomonella species and distinguishing it from R. zephyria which can benefit commercial
apple crops and measures needed to protect infected crops.
2. The hypothesis of the R. pomonella/R. zephyria paper was the possibility that the
two species can be differentiated through examination of surstylus shape for the male
flies and aculei shape for female flies. These two morphological differences when in
combination with the size of the parts examined could potentially offer a much more
reliable and accurate way of differentiating between the two species which is a valuable
tool for commercial apple crops facing invasion by the harmful R. pomonella.
Additionally, the researchers hypothesized that the species-specific shape of the aculei
and surstylus of each species would be consistent between varying host fruits and
collection areas, indicating that this identification method would be applicable to a wide
range of locations and commercial apple crops.
3. The researchers went out into infested orchards and collected fallen apples and
hawthorn and snowberry fruit directly from trees in the Washington and northwestern
Oregon areas in 2007 and 2008. The infested fruits were then brought into a laboratory.
Puparia of the flies were collected from the harvested fruits, stored, and allowed to
mature before being euthanized. Flies were then organized into varying groups and
analyzed.
4. The main statistical test used to address the hypothesis was called canonical
variates analysis, which is abbreviated CVA throughout the paper. Specifically, the
program CVAGen6o was implemented in analysis for the data. The authors describe
CVA analysis as “a multitaxis discriminant function and an ordination method for
depicting differences visually and for testing the ability of variables to correctly predict
group [to which each fly belongs to] differences based on measurements.” In a nutshell,
this means that the CVA analysis will allow for the detection of morphological shapes
that best distinguish one species from the other using the shape of the surstylus and aculei
in order to find a more accurate means of identifying R. pomonella and R. zephyria
accurately.
The graph that showed the results of CVA most clearly to prove the researchers
hypothesis, with regards to surstylus shape, was Figure 4 which was a scatter plot
produced from CVA results of both R. pomonella and R. zephyria. The data are clearly
clustered in two groups on the scatter plot – with the data representing the sursytlus shape
of the six different groups of R. pomonella almost exclusively to the right on the scatter
plot, with the surstylus shape of the two different groups of R. zephyria exclusively to the
left on the scatter plot. However, it should be noted that according to Figure 9, a
scatterplot based on CVA results of aculei shapes of the two species, aculei shape for
females is not nearly as reliable means of species identification as surstylus shape is for
males – as evidenced by a lack of two distinct groups of data on the scatter plot.
5. I believe that the hypothesis was proved in the article. The researchers proved that
the surstylus shape of male flies differed between R. Pomonella and R. zephyria through
the use of CVA and MONOVA analyses, demonstrated in part by Figure 4 as mentioned
above and additional data found throughout the paper. However, the researchers failed to
prove that aculei shape would be a highly accurate means for female identification and
differentiation of the two species. The two species had too similar aculei shape to be a
reliable means of identification. However, their results still support the hypothesis that
the shapes of the aculei between the two species do in fact differ – the authors reported
that analysis of aculei shape demonstrated 85.3% accuracy in species identification for
female flies. However, this means of identification is not as accurate as surstylus
identification in male flies.
The researchers were able to identify each species most accurately using surstylus
and aculei configuration and shape in addition to wing shape and “multiple linear body
measurements.” This extensive approach offers the most reliable means to species
identification for male flies.
Additionally, the researchers also proved their hypothesis that the surstylus and
aculei shapes did not vary between location of harvested fly samples, with one notable
exception being the pom BH c WA group which may have exhibited hybridization.
6. The story of the apple maggot paper can best be summed up as follows: The
morphology of two fly species R. pomonella and R. zephyria are very similar at first
glance. However, the two species are often confused for one another which is
problematic as R. pomonella is a harmful pest that damages commercial apple crops in
the United States. The researchers examined the morphology of the surstylus and aculei
of male and female flies of each species and found that analysis of the size and structure
of these two structures, in addition to the analysis of wing shape and other measurements
provided almost entirely accurate identification of the two different species. This new
accuracy can ensure proper identification of the harmful R. pomonella-infested apple
crops and the appropriate subsequent means of treating the trees to rid them of maggots.

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