The Genetic and Developmental Basis of Divergence in Drosophila

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The Genetic and Developmental Basis of Divergence
in Drosophila

• By
• Karen Richardville
• Bishop Dwenger High School

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Project 1

• the evolution of reproductive isolation
  between different species
• of African Drosophila

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My research was on the hybrid femaleIf given a
choice of mates will she choose one with traits
like her mother or traits like her father?
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We will test 3 hybrid female lines, produced
from different strains of female D. simulans
crossed with male D. melanogaster

• Maz 1 X IN(1)ABfm
• Maz 2 X IN(1)ABfm
• Maz 6 X IN(1)ABfm

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The day before the mating trials the males are
put on colored food which will show as a stripe
in their abdomen. One will be on green food, the
other on red food.
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For the mating trial, the females are placed in a
vial to which are added the same number of sim
males and an equal number of mel males. Maximum
of 15 flies (5 each) per trial vial.
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During the mating trial remove any mating pair to
a CO2 plate to determine which male was chosen by
the colored stripeon his abdomen
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Place all Maz1 and Maz 6 hybrid unions on food to
see if any viable offspring are produced
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Possible results1. yes there is a preference
for either the Sim male or the Mel male2. there
is no preference3. females dont choose and
there is no mating
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Comparison of hybrid lines
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Mating trials of hybrid females
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Conclusion

• It appears that there is a preference for the D.
  simulans male.

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Follow Up

• More trials must be done before the conclusion
  will be statistically significant
• However these results are strong enough to bring
  up further questions

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Questions

• Why is a hybrid with predominantly expressed mel
  genes choosing a sim mate?
• Are any of the courtship genes in the hybrid from
  her sim mother?
• Do all hybrids always get the same genes
  expressed from the father and the same genes from
  the mother expressed or is it random?
• Which genes are expressed sim and which are mel?

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Project 2

• the evolution of abdominal pigmentation between
  within different species of the Drosophila
  cardini group which inhabit the Caribbean Islands
  and Central and South America

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We want to show that abdominal pigmentation
variation is truly intraspecific
polymorphism(many types of the same species) and
not interspecific divergence (two or more
separate species).
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Female-neomorpha
Male-neocardini
Female-polymorpha
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Understanding the origins of diversity is
fundamental to the conservation of existing
species. Current efforts to preserve
biodiversity depend on accurately documenting
levels of variation that at this point in time
remain unknown.
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Recent genetic studies have found what are
supposed to be single species are in fact
harboring molecular diversity and also lineages
that are genetically distinct
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As more studies come to bear on this issue the
implications for current estimates of
biodiversity are huge!!
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The Drosophila cardini group is an ideal model
system to address Neotropical diversity because
of its geographical distribution and
morphological differences
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Morphological differences
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The COII locus (from mitochondrial DNA) is a
neutrally evolving locus that is not under
selection. This is one of the genes studied.
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Mitochondrial DNA
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The COII locus is used to estimate divergences
among populations from all species examined
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Collections have been made from Uruguay, Brazil,
Venezuela, Trinidad, Costa Rica, Panama and Mexico
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All flies were individually examined and
phenotypedAt least 10 flies from every
population were set aside to be sequenced
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My involvement in this project begins here.I
worked with groups of 9 individual flies from
various locations
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I extracted their DNA, ran a PCR, and then ran an
electrophoresis to determine if there was
amplifiable DNA.
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1 2 3 4 5 6 7 8

• Electrophoresis results
• 100 base pair ladder
• Sample
• Sample
• Sample
• Sample
• Sample
• Blank
• Negative control X 10
• Sample
• Sample
• Sample
• Sample
• Sample
• Sample
• Blank
• Blank

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The brightest band is the 600 base pair band on
the ladder These results show the sample DNA at
about 700bp. This is what we want to see to be
able to continue
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This ends my part.However since we have
amplifiable DNA we can continue
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Using the PCR product we just made, we run
another PCR to tag it with flourescent dye to
color code the nucleotides
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This is the final product which is sent to be
sequenced. All the DNA fragments are separated
out and the 4 dye colors are translated to As,
Cs, Ts and Gs ( the 4 nucleotides that make up
the DNA molecule)
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All loci will be tested for1. evidence of
natural selection (neutrality)2. differentiation
between populations and levels of gene flow will
be estimated (population structure)
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The raw sequenced data is analyzed using several
different computer programs
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Sequence scanner

• examines an electropherogram

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MEGAMolecular Evolutionary Genetic Analysis

• Groups the DNA sequences according to the
  similarities in nucleotide sequence and then
  produces a phylogenetic tree or phylogeny

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Hypothesis Taxa of the mainland D. cardini
subgroup will be monophyletic across their large
neotropical ranges (ie. One species)
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Further questions

• 1.The phylogenetic tree shows there are possibly
  2 groups, are these separate species?
• 2. What caused the differences between these 2
  groups?
• - geographical?
• - ecological?
• 3. What are the ancient events relative to the
  current events that might explain their
  divergence?

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Many thanks to

• Dr. Hope Hollocher
• Heather Eisler
• Erin Penton
• Notre Dame RET program