The Effects of Temperature on Rates of Metamorphosis in Vanessa cardui
Rose Park and Laura Chan
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
The objective of this study was to determine if environmental temperatures
could potentially be a contributing factor in the rate of metamorphosis in Vanessa
cardui, commonly known as the Painted Lady butterfly. The researchers did this by
testing the length of time in days each subject took to progress from the larval stage to
the pupa stage as a chrysalis in two groups incubated at different temperatures. The
reasoning for this study was that if the subjects incubated at the higher temperature,
27.7C, it will progress to the pupa stage at a significantly greater rate than those
incubated at the lower temperature, 22.2C, temperature could be a contributing factor
to the rate of metamorphosis. The investigators hypothesized the higher temperature of
incubation would yield a greater rate of metamorphosis (already mentioned) than the
lower temperature. The hypothesis was tested by recording the number of days for each
caterpillar in each test group it took to progress from the larva to pupa stage. The mean
number of days it took for the higher temperature group was 11.450.65 days (S.E.M.,
N=20), while the mean number of days for the lower temperature group was 15.570.16
days (S.E.M., N=24). An unpaired, one-tailed t-test was used and the result suggests
that there is a significant difference in metamorphic rate between subject groups
(p0.05). Conclusively, temperature may be a strong contributing factor in metamorphic
rate of the V. cardui species.
Introduction
Metamorphosis describes the physical change of some organisms from Class Insecta
from a larval stage to its matured form. Signaled by the release of the prothoracotropic hormone
( PTTH ) , metamorphosis, particularly in the group Lepidoptera, begins by ecdysis: the shedding
of the hard exterior exoskeleton. The exoskeleton within this group is the chrysalis. By
decreasing the levels of juvenile hormone present, the insect may begin metamorphosis through
its final ecdysis as a larva. The group Lepidoptera follows this biological pattern, as well as
specific circadian rhythms to calculate their metamorphic rate, in order to provide a biological
rhythm (Lampel et al. 444). This method of photoperiod tempo is intertwined with the nutrition
present for the specific species. Thus, this specific group of the class Insecta requires a rhythm to
evolve to its adult stage. The length of time require to reach its adult stage can be adjusted in
accordance to the nutrients available (Kelley and Debinski 315). The rhythm should vary within
the factors affecting the rate of metamorphosis. According to Pollard within his study titled
Temperature, Rainfall and Butterfly Numbers, there exists a direct correlation between weather
conditions and butterfly populations (820). Known for their migration patterns, the species
Vanessa cardui, commonly known as the Painted Lady, travels to warmer environment comes
wintertime, as to provide a suitable environment for the larval stages (Scott 18). This migration
patterns allows V. cardui to be the most widely spread butterfly species (Nunez and Marrero 2).
Thus, the species of painted ladies may endure a variety of temperatures with its large dispersal.
Several researchers have previously studied the effects of temperature on metabolism and
metamorphosis. While some maintain that an increase in temperatures may not lead to increased
growth rates in temperate insects, others uphold that temperature does play a strong role in the
body size and growth strategies that contribute to metamorphosis (Gotthard 471).The
investigators’ objective is to study what the optimal temperature would be for Vanessa cardui to
begin metamorphosis into its adult stage as a butterfly. The investigators hypothesize that
warmer temperatures will yield a greater rate of metamorphosis in V. cardui than a cooler
temperature. The greater temperature best fitting the temporal regions of North America will
provide an optimal environment to begin ecdysis to an adult stage than a temperature slightly
lower. Metamorphosis should begin at a faster rate at a higher temperature if the hypothesis is
correct.
Materials and Methods
To collect data for this experiment, investigators recorded the amount of days it took for
each Vanessa cardui caterpillar to begin its pupa stage from the day it began its larval stage, or
the day it hatched. There were many variables that needed to be accounted for to ensure the least
variability in the subjects such as age, type and amount of food source provided, living habitats,
and daily photoperiods. Thus, all larva hatched on the same day, all were provided with an equal
amount of artificial diet that filled the bottom of their habitat to ensure they could each eat as
much as they need, all resided in plastic rearing cups provided by Mulberry Farms, and both
variable groups had a photoperiod imitated by a lamp providing 12 hours of light and 12 hours of
darkness in each incubator, a typical photoperiod for the summer season, when Vanessa cardui
are most abundant. The variable being tested was temperature: one group of larva in an incubator
at 72F, or 22.2C, and another at 82F, or 27.7C. Both incubators used were in the Saddleback
Biology Student Research Laboratory.
Sixty-one larva were obtained for this study, however, only the larvae that survived to
progress into the pupa stage were used included in the sample size. In the test group incubated at
higher temperature, out of the original 33 larvae, 20 were included in the sample size. Likewise,
for the other test group, out of the original 28 larvae, 24 were included. Overall, 72% of the
originally obtained larva survived to become a chrysalis. The larva were 3 days old when
individually transferred and separated from a single large Petri dish into 5 rearing cups, each
with approximately 10-15 larva. Three of the rearing cups were placed in an incubator set at
27.7C with a lamp on a 12-hour on and 12-hour off timer, while the other two were placed in an
incubator set at 22.2C with a similar lamp setup. The caterpillars were observed daily and the
investigators recorded the day each larva began pupation. From the raw data, the number of days
it took each caterpillar to reach the pupa stage from hatching was calculated.
All data was were transferred to MS Excel (Microsoft Corporation, Redmond,
Washington) where further analysis took place. To analyze the data collected, investigators
calculated the mean number of days it took each caterpillar to proceed from larva to pupa stages
for each of the two temperature groups. Using an unpaired, one-tailed t-test, statistical analysis
was performed, which provided the p-value needed to either reject or support the null hypothesis.
Results
Upon viewing the specimens, the chrysalis size of the groups placed in the higher
temperature of 27.7°C were significantly larger than those placed in the lower temperature. The
specimens in sample groups of the Vanessa cardui incubated at 27.7 °C cocooned after a mean
time of 11.45 days, while the mean time for subjects incubated at 22.2°C was 15.57 days. To
determine if differing temperatures quickened the rate of metamorphosis, a one-tailed t-test
assuming unequal variances was completed. The null hypothesis that the temperature of
incubation provides no significant input in the rate of metamorphosis can be rejected (p<0.05)
(Table 1).
Table is not necessary, since you already have the bar graph.
Figure 1. The mean number of days for subjects to progress from larva to pupa stages for two
different temperature groups (one-tailed t-test with unequal variances, p<0.05).
If you mention the p-value on the figure caption, please elaborate more. What is its
significance??
Pls indicate what the error bar means.
Need to insert the title of the x-axis
(optional )
Change the color on bar graphs so it'll be visible on B&W..
Figure 2. The larval and cocoon stage incubated at 22.2C.
Need a much clearer photo.. I can't see anything.. and yes. I did opened my eyes!
Figure 3. The larval and cocoon stage incubated at 27.7°C.
Discussion
The mean incubation period of Vanessa cardui incubated at 27.7 °C is 11.45 days, while
those incubated at a lower temperature 22.2 °C is 15.57 days. Since the p-value is (enter pvaluehere), the null hypo can be rejected... Thus, the temperature of incubation during the larval
to cocoon stage does play a significant role in the rate of metamorphosis. The hypothesis of a
higher temperature increasing the rate of metamorphosis in Vanessa cardui was correct.
According to Kelley and Debinski, the temperature of incubation during the larval stage of the
species Vanessa cardui was a significant factor in development. The study indicated that larval
stages of Vanessa cardui had the capability to extending the necessary growth period to develop
into the adult form, in reference to the effects of food limitations (Kelley and Debinski 320).
Upon incubating a total of 5 groups of this particular species, the data depicts that the
temperature did indeed affect the growth period of the Vanessa cardui. The size of the
caterpillars during the larval stage were visibly smaller in the lower temperature groups than that
of the caterpillars incubating at 27.7°C (Fig. 2). Although Kelley and Debinski stated that
Vanessa cardui had the ability to elongate their growth period before maturing into a cocoon, the
data clearly reflects that this elongation process does not necessarily mean the larval stages will
reach the same lengths before maturing into their chrysalis form. The cocoons of the caterpillars
incubated at 27.7°C were also significantly larger in comparison to those of the specimens held
at 22.2°C (Fig. 3). The time to reach the smaller cocoon size huh? you meant 27 degree C? ,
however, was longer as the mean amount of days to begin cocooning was 15.57 days (Table 1).
These results indicate that Vanessa cardui do have the capability to elongate their growth periods
before reaching their adult stage; this elongation, however, is not in reference to the lengths of
the caterpillars as the size of both the cocoon and larval stages of the lower temperatures were
visibly smaller.
Given an ample food supply and continuous light source, the only variable determined
was the temperature of incubation. Thus, the circadian rhythm of Vanessa cardui could only be
affected through temperature control. According to Pollard’s study titled Temperature, Rainfall
and Butterfly Numbers, weather was hypothesized as a factor related to butterfly populations.
The data of this experiment clearly depicts that the temperature of incubation, which would
mimic the representative weather conditions, did indeed contribute to the rates of metamorphosis
from larval to cocoon in Vanessa cardui. Higher metamorphosis rates, which yielded by
incubating the larvae at a higher temperature would affect the butterfly populations to appear
more rapidly in the warmer temperatures. The conditions of which the larval stages are being
held do indeed affect the populations of the adult stage. The results of this experiment could
indicate that PTTH became more readily available at 27.7°C, its plausible specific heat, or that
the larval stages began cocoon at a higher temperature as a cause of expending less energy on
metabolism. The data merely reflects temperature’s effect on Vanessa cardui’s metamorphic
rate.
Throughout the world, Vanessa cardui is the most distributed butterfly (Marrero and
Nunez 61). This experiment may suggest that Vanessa cardui’s population is directly related to
the environment in question. In short, the warmer climates must house the larval stages, while
the milder temperatures would provide a niche for the adult stages. Vanessa cardui are known to
migrate, which would (huh?).. can you finish the sentence...
The effects of temperature can clearly be seen through the data of this experiment.
However, the data reflects the first generation of incubated caterpillars. The caterpillars of the
sample groups were originally from Vanessa cardui held at 27.7°C; the temperature of
incubation held at the butterfly farm. The data suggests that higher incubation temperature
would induce a faster rate of metamorphosis, regardless of the generation. Had this experiment
been performed again, the data of the larval from the original sample group should be examined
and taken into account. The results of this experiment would be a true test on the rate of
metamorphosis based upon temperature of incubation.
Acknowledgements
The investigators acknowledge Mulberry Farms for supplying the larvae, artificial diet and
rearing cups and Professor Steve Teh for assisting in the Biology Student Research Laboratory.
Literature Cited
Debinski, D. and Kelly, L. (1999). Effects of larval food-limitation on Vanessa cardui Linnaeus
(Lepidoptera: Nymphalidae). The American Midland Naturalist. 141(2): 315-320.
Gotthard, K. (2004). Growth Strategies and Optimal Body Size in Temperate Pararginii
Butterflies. Integrative and Comparative Biology. 44(6). 471-479.
Lampel, J., Briscoe, A., Wasserthal, L. (2005). Expression of UV-,blue-, long-wavelengthsensitive opsins and melatonin in extraretinal photoreceptors of the optic lobes of hawkmoths.
Cell Tissue Res. 321: 443-458.
Marrero, L. Nunez, R. (2005). Vanessa cardui Poey (Lepidoptera: Nymphalidae), a new report
for soybean in Cuba. Rev. Protección Veg. 20(1): 60-61.
Pollard, E. (1988). Temperature, rainfall and butterfly numbers. J Appl Ecol, . 25: 819-828.
Scott, J.A. (1992). Direction of spring migration of Vanessa cardui (Nymphalidae) in Colorado.
J Res Lop . 31 (2): 16-23.
Go to
http://entnemdept.ufl.edu/all_journals.htm
for journal abbreviations!
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s):__ Rose Park and Laura Chan
Title:__ The Effects of Temperature on Rates of Metamorphosis in Vanessa cardui
Summary
Temperature does affect the mean incubation period of Vanessa cardui. Higher temperature
would speeds up the metamorphosis process due to the availability of PTTH at warmer climate.
The temperature also affect the size of caterpillars, higher temperature would yield bigger size,
while lower temperature would yield smaller size.
General Comments
The investigators had published a strong paper with some minor flaws. The minor flaws include
forgetting to label the x-axis, stating the same information twice (data table and graph), some
affect vs. effect issues and wrong formatting of the journal abbreviation in literature cited.
Investigators need to see http://entnemdept.ufl.edu/all_journals.htm for help on abbreviation of
their references.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and
minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
This paper was a rough draft
Please see above for revision. (red font - bold)
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