The document summarizes an experiment that investigated the effect of varying levels of ultraviolet (UV) light exposure on the regeneration abilities of the brown planarian (Dugesia tigrina). Planarians were exposed to UV light for 0, 1, 3, 6, 9, and 12 hours. Regeneration was assessed on days 1, 4, and 7 after exposure. Results showed that as UV exposure increased, the percentage of fully regenerated planarians decreased while the percentage that died increased. Higher UV exposure impaired blastema formation and morphallaxis, the processes required for proper regeneration. A chi-square test found a significant difference in death rates depending on UV exposure level. The goal was to determine the effect of UV

1. Alvarado, Alejandro Sánchez and Peter W. Reddien. FUNDAMENTALS OF PLANARIAN REGENERATION
Vol. 20: 725-757 (Volume publication date November 2004)
http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.cellbio.20.010403.095114
Carolina Protozoa and Invertebrates Manual, 1977. http://web.esc20.net/livsci/pdf/Handouts/LMP-
13%20Planaria.pdf
The Columbia Electronic Encyclopedia, 6th ed. 2007, Columbia University Press.
"Planarian”. http://www.infoplease.com/ce6/sci/A0839279.html
Sparling, Brien. Ultraviolet radiation. http://www.nas.nasa.gov/About/Education/Ozone/radiation.html
Increased exposure to UV light appears to impair proper blastema formation and morphallaxis in Dugesia
tigrina. The number of fully regenerated planarians increased as the UV exposure decreased, which
demonstrated that UV has the ability to damage cell structures and impair the repair of cells. Amplified levels
of UV caused more planarians to die, which demonstrated that they could no longer regenerate as expected.
This is most likely due to cell damage at a nuclear level, which would prevent the proper coding for proteins
and lipids required to rebuild the planarian at the damaged site.
Dugesia tigrina is particularly sensitive to light and in its natural habitat is generally found in dark
environments, so it is possible that any exposure to light, including exposure to light during observations and
rotations, could have caused environmental stress to the planarians and increased their inability to fully
regenerate. The osmolarity of the distilled water that was used in the experiment may have been different from
the osmolarity found in the planarian’s natural environment, and this could have also affected the way in which
the planarians regenerated.
Future research on Dugesia tigrina may include larger sample sizes, which would enable more accurate
results to be recorded, and increase the accuracy of any statistical tests performed. A larger sample size
would better represent the population as a whole. An effort to reduce any other outside effects of regeneration,
such as reducing light sources other than the UV light source, may also help to yield more accurate results.
A Chi-square test was performed for the death rates of planarians to determine whether there was a
significant difference of regeneration depending on differing levels of UV radiation exposure. The calculated
value was determined to be 12.22, and at a degree of freedom of 5 and a probability of 5% the critical Chi-
square value was 11.07. This demonstrated that there was a significant difference in the rate of death of brown
planarians based on ultraviolet exposure. The data also indicated a trend that death rates increased as UV
exposure increased.
The percentages of planarians based on full regeneration, partial regeneration, and death demonstrate
that as UV exposure increases the fully regenerated planarians decrease in percent and the death rates of
planarians increase. Also, as UV exposure increased, the blastema failed to form correctly, and improper cell
division was found more frequently at the damaged site. One day following the cutting of the planarians the
blastema was beginning to form in the control and the 6-hour test subjects, as seen in Figures 2.A and 2.B, but
in the 12-hour subject the blastema region had failed to properly form, as seen in Figure 2.C. Planarians that
were exposed to 12 hours of exposure also demonstrated an incomplete blastema, which led to the pharynx
being ejected from the mouth, as in Figures 2.F and 2.H. In Figure 2.I the failure of the blastema to form
resulted in incomplete regeneration of the head of the planarian, as can be seen by the indentation in the
epithelium.
The goal of the experiment was to determine what effect exposure to variable levels of ultraviolet light
had on the regeneration of Dugesia tigrina, the brown planarian.
Planarians have the ability to regenerate completely into two individuals after being bilaterally cut. This
is due in part by neoblasts, groups of stem cells scattered throughout the organism’s tissue, and the process
of morphallaxis which remodels pre-existing tissue to restore symmetry and function. After sustaining injury,
somatic cells around the neoblasts at the blastema, a structure that forms at the wound site, are consumed to
complete the regeneration process. This accounts for the lost mass of the individuals while simultaneously
permitting their complete return to normal morphology (Alvarado and Reddien 2004).
The species used in the study, Dugesia tigrina (brown planarian), is a freshwater inhabiting free-living
flatworm native to the North American continent. Dugesia tigrina is of the Phylum: Platyhelminthes, Class:
Turbellaria, and Order: Tricladida. Known for their regenerative abilities, the species has been the subject of
scientific study for decades. Brown planarians are hermaphroditic and prefer to reproduce sexually, but are
capable of asexual reproduction by splitting into two individuals from the middle. The length of these animals
varies between 1/8th
of an inch and 1 inch. Brown planarians are scavenging carnivores that digest food
externally using their pharynx before withdrawing it into their gut. Two photoreceptors on the head aid
planarians in avoiding direct light ("Planarian,” 2007).
What we call ultraviolet light represents a wavelength band (400-150nm) of the electromagnetic
spectrum that has a frequency too high for the human eye to perceive but is weaker than X-rays (Sparling,
2001). Ultraviolet radiation can penetrate cells and directly damage the genetic material in the nucleus,
raising the possibility for mutation or growth disorders (cancer) to develop in addition to cell death. DNA
absorbs UV-B radiation, and the energy can dislodge nitrogen bases from their configuration or otherwise
break the strands. Ultraviolet light is generated by the sun, but is also artificially produced for use in tanning
beds and sterilizing laboratory equipment.
In the pilot experiments, attempts were made to introduce variable concentrations of Aloe Vera juice to
the water-filled fingerbowls that housed the planarians. A concentration gradient ranging from 50% to 5%
Aloe Vera juice resulted in 100% mortality of all subjects. A second attempt featured a concentration range
from 5% to 1%, with majority mortality. It was at this point that the Aloe Vera juice was removed from the
experiment’s design.
The UV exposure ranges were determined also within a pilot experiment, which demonstrated that after
18 or more hours of exposure, the subjects experienced 100% mortality. The upper threshold of 12 hours was
later the benchmark for exposure times in the final experiment.
Distilled water was added to each of the 6 ~100mL fingerbowls, nearly filling them. The planarians were
pulled out of the specimen jar via pipette and squirted onto a glass slide, where they were cut in half with a
scalpel. The severed head ends were placed in one bowl, while the tails were placed in another. This process
was repeated two more times, with a total of 10 planarian halves per fingerbowl. After labeling the bowls and
sealing the tops with clear polyethylene plastic wrap, they were placed on a rack in an environmental
chamber as in Figure 1.
The environmental chamber was prepped to hold a constant 19 degrees Celsius (Carolina, 1977). The
UV lamps were placed on the top rack, with another rack roughly six inches beneath it as a holding area for
the planarian bowls undergoing exposure. The chamber’s internal fluorescent lights were turned off, except
for the one on the bottom rack. A black garbage bag was wrapped around the rack to shield the exposed
planarians beneath from further exposure. The control specimen fingerbowl was placed on the bottom of the
chamber at experiment start. The remaining five bowls were placed on the holding rack. After a time passage
increment of one hour, a labeled specimen fingerbowl would be moved to the bottom of the chamber. This
was to be repeated at the intervals of 3, 6, 9, and 12 hours, until all specimen bowls were on the bottom.
Exposure was not repeated. On the first day (after exposure), as well as the fourth and seventh days,
photographs were taken of one specimen from each bowl to observe the extent of the subject’s regeneration.
Figure 1
Figure 2.CFigure 2.BFigure 2.A
Figure 2.G
Figure 2.FFigure 2.EFigure 2.D
Figure 2.IFigure 2.H
Figure 3