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
In this study, the objective 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(27.7C) progressed to the pupa stage at a significantly greater rate than those incubated at the lower temperature (22.2C), 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 in V. cardui than the lower temperature. The hypothesis was tested by recording the number of days it took for each caterpillar in each test group it tookto progress from the larva to pupa stage. The mean number of days it took for the higher temperature group was 11.450.65 days (S.E.M., N=20), while the mean number of days for the lower temperature group was 15.570.16 days (S.E.M., N=24). An unpaired, one-tailed t-test was used and the results rejected the null hypothesis that there is no significant difference in metamorphic rate between subject groups (p<0.05). 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, known as 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(unclear, reword). 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 72F, or 22.2C, and another at 82F, or 27.7C. 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(typo?)in the sample size. In the test group incubated ata 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 27.7C with a lamp on a 12-hour on and 12-hour off timer, while the other two were placed in an incubator set at 22.2C 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 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).
Incubation Temp / 27.7°C / 22.2°CMean / 11.45 / 15.57
P value
(one-tailed) / 1.49989E-06
Table 1. The mean number of days it took subjects to progress from larval to pupa stages.
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).shouldn’t you actually put your p value?
Figure 2. The larval and cocoon stage incubated at 22.2C.
Figure 3. The larval and cocoon stage incubated at 27.7°C.
Discussion
The null hypothesis can be rejected, the p value is significantly smaller than 0.05. 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(1999). The study indicated that larval stages of Vanessa cardui had the capability of 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 was 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, 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(1988). 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. These rates would thus effect the butterfly populations of the specified sample groups as butterflies appeared 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(? Extra 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 a higher incubated 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. (somewhat redundant paragraph)
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-wavelength-sensitive 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. Journal of Applied Ecology. 25: 819-828.
Scott, J.A. (1992). Direction of spring migration of Vanessa cardui (Nymphalidae) in Colorado. Journal of Research on the Lepidoptera. 31 (2): 16-23.
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s):______Park and Chan______
Title: The Effects of Temperature on Rates of Metamorphosis in Vanessa cardui
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
The investigators in this study were interested in the effects of temperature on the metamorphic rate of the Painted Lady butterfly or Vanessa cardui. They hypothesized that the higher the temperature, the sooner the larva will grow into the pupa stage. Two groups were tested; both were fed the same amount of food and kept in similar controlled environments. The only difference were one was incubated at 27.7C and the other at 22.2C. The number of days it took for them to grow into the pupa stage was counted and after an unpaired, one-tailed t-test was run, the p value (p<0.05) rejected the null meaning there is a significant difference in the metamorphic rate of the butterflies. Not only did the larva in the warmer environment mature faster, but they were also larger in size based on the elongation process. This can also suggest that the PTTH hormone, released for metamorphosis, might become more available at warmer temperatures.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current state of knowledge.
The paper did an excellent job in the introduction and methods and materials sections. The discussion became a little redundant as the same claims and information were repeated. A better job could have been done on that section, which is meant to be the most important part of the paper. The information provided in this paper could be important to our current state of knowledge. It’s not very crucial, but still essential.
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 final versionThis paper was a rough draft
-A recommendation would be not to repeat the scientific name of the butterfly every single time. V. cardui could be used instead of the full name.
-The citations should have the year and not the page number. The page number is only needed when quotations are used.