Microevolution: Experimentation With Selective Pressures in Drosophila melanogaster

1

• Microevolution Experimentation With Selective
  Pressures in Drosophila melanogaster
• Sean J. Wallace
• Patrick J. Doyle

RESULTS The results from the experiment support
the hypothesis, wherein it was predicted that the
wild-type flies would flourish in both
experimental environments. A significant
increase in the wild-type to ebony populations
was observed, respectively. Fluctuating Light
Environment (12/12 hours) F1 Generation F2
Generation 30 ebony 42 ebony 15 wild-type 120
wild-type Dark Environment (24 hours) F1
Generation F2 Generation 30 ebony 74 ebony 15
wild-type 209 wild-type

INTRODUCTION/OBJECTIVE The purpose of this
research was to investigate Charles Darwins
theory of natural selection by the manipulation
of selective pressures in the study of
microevolution involving Drosophila
melanogaster. HYPOTHESIS When the selective
pressure is applied to the populations of D.
melanogaster, the most well-endowed of the
population will be more successful and survive.
In this case, it was predicted that the wild-type
flies would flourish in both experimental
environments, being that the wild-type alleles
are either homozygous dominant (RR) or
heterozygous (Rr), while the ebony allele
presents as a recessive trait (rr).
Figure 1. Population cages were created as a
habitat for the Drosophila melanogaster
populations.
MATERIALS Drosophila melanogaster media
- Apple sauce - Oatmeal -
Yeast - Vinegar Crushed ice 8 50mL
conical tubes 2 - Gladware food storage
containers 2 - stockings in place of lids 2
petri dishes 2 flybrush/paintbrush 1 tube of
silicone adhesive 1 vial ebony Drosophila
melanogaster 1 vial wild-type Drosophila
melanogaster 1 stereoscope
Discussion Evolutionary theory, as presented by
Charles Darwin, refers to the change in gene
frequency of a population. This in turn leads to
the natural selection of the more well suited
species. It should be noted that each population
cage was primed with a high ebony allele
frequency. This was to give their recessive
genes a chance to be more well-represented in the
ensuing results. Based on the experimental data,
a change in gene frequency through the
manipulation of micro-evolution was observed.
The genotype in the populations favored the
wild-type flies (RR and/or Rr). As observed
throughout the study, the wild-type populations
out-competed the ebony populations when the
selective pressure was applied thus, the
wild-type flies established themselves as the
more well suited and successful population in
both the control as well as the experimental
environments. These modest experiments offer a
small glimpse in to the contentious debate of
evolution theory.

• PROCEDURE
• The selective pressure chosen was light.
• More specifically, the influence of light in
  relation to sexual activity of two distinct
  populations of Drosophila melanogaster ebony
  (rr) and wild type (RR/Rr).
• In order to investigate microevolution, two
  populations of Drosophila melanogaster were
  raised and manipulated in both the light and dark
  environments.
• Initially, four population cages were
  constructed (Figure 1).
• Next a suitable media for the Drosophila was
  created and placed it into two of the 50mL
  conical tubes on two of the four population cages
  (Figure 1).
• Using a cooling anesthetic method, the flies were
  immobilized into a more manageable state (Figure
  3).
• Once separated, 30 ebony (rr) and 15 wild-type
  (Rr or RR) Drosophila were placed, respectively,
  into the remaining two conical tubes of two
  population cages. The amount of ebony flies was
  doubled to begin in an effort to give the
  recessive alleles an increased chance (Figure 4).
• To implement the selective pressure, one cage was
  placed in a fluctuating light environment (12/12
  respectively), and the remaining cage experienced
  a 24 hour dark environment (via a tub covered
  with tinfoil) (Figure 2).
• 
  

Figure 2. Experimental environments. Under the
fluorescent bulb, a 12 hour light and 12 hour
dark oscillation was induced. Additionally, a
constant 24 hour dark environment was induced
(seen near bottom of Figure 2) .


Figure 3. D. melanogaster under stereoscope. To
the left is an ebony fly (rr) and to the right is
a wild-type (RR/Rr).
WORKS CITED Bothamley, J. (1993). Dictionary of
Theories. London Gale Research     International
. Care, maintenance and manipulation of
Drosophila. (n.d.). Retrieved September     28,
2006, from http//biology.arizona.edu/sciconn/less
ons2/Geiger/     intro2.htm Evolution Theory
Science. (n.d.). Retrieved September 28, 2006,
from     http//www.ucmp.berkeley.edu/history/evo
theory.html Futuyma, D. J. (1982). Science on
Trial The Case For Evolution. Westminister,     
Maryland Alfred A. Knopf Inc. Salata, M.
(2002, May). Evolution Lab with Drosophila.
Bioscene, 28(2), 3-6. Theory of Evolution.
(n.d.). All About The Journey. Retrieved
September 28,     2006, from http//www.allaboutt
hejourney.org/theory-of-evolution.htm
Figure 4. F2 generations of ebony (left) and wild
type (right).