Download Effects of Anthropogenic Events On Pseudoboletia indiana

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Ginna Vick
Dr. Teymuroglu
BIO 342
27 November 2016
The Effects of Anthropogenic Events On Pseudoboletia indiana
“On my honor, I have not given, nor received,
nor witnessed any unauthorized assistance on this work.”
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Abstract:
To further understand how climate change and dropping levels of pH will affect marine
species, an experiment on an urchin species Pseudoboletia indiana was run. The experiment
included different temperature and pH levels on P. indiana reproduction and development. A
series of statistical tests analyzed whether i) there was a linear relationship between percent
fertilization and percent gastrula formation ii) the pH levels had a relationship with percent
gastrula formation and lastly iii) there was a significant difference of high gastrula formation
given an experimental versus a control temperature. Each of these questions help piece together
information concerning the ability of P. indiana to survive in harsh conditions. By running the
statistical tests, it was found that there was a linear relationship between percent fertilization and
percent gastrula formation, that the pH levels did have a relationship with percent gastrula
formation and that there was no significant difference of high gastrula formation given
experimental or control temperatures.
Literature Review:
In this study, the sea urchin, Pseudoboletia indiana was analyzed because it is an
important species to Australia and Tasmania and could potentially be affected by anthropogenic
climate change. Human created CO2 and climate change are causing ocean acidification and an
increase in ocean temperature. Increased carbon dioxide in the atmosphere indicates that high
levels of CO2 are being absorbed in the ocean and changed to carbonic acid. When this occurs,
the acid changes into hydrogen and bicarbonate ions which then decreases pH. By 2100, the CO2
concentration will jump from 300-380 parts per million (ppm) to 450-1000 ppm (Byrne et al.,
2009). A decrease in pH is detrimental to marine invertebrates and impacts growth, reproduction,
and development as well as decreases the number of motile sperm therefore decreasing
fertilization success (Byrne et al., 2009).
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While CO2 increasing is detrimental to marine invertebrates, increased temperature can
also affect physiological function, growth, and development (Byrne et al., 2009). Through
research of a different urchin species, it was found that a temperature increase of 3°C was
detrimental to them. While some organisms may be able to adapt to their environment using
phenotypic plasticity, others may not be able to (Foo et al., 2014). For example, some urchins
may be able to sense the temperature which indicates when they should spawn rather than
relying on season (Foo et al., 2014). Some marine invertebrates are able to distribute towards the
poles to escape rising temperatures, while others cannot because they may have long generation
times or are unable to find a suitable habitat.
In order to determine how well P. indiana would adapt to anthropomorphic changes in
the ocean, an experiment of three pH levels, two temperatures, and different male and female
crosses was completed. The experiment had three different pH levels of 8.1, also known as the
ambient pH, 7.8, and 7.6. There were two different temperatures, one at 22 degrees Celsius and
another at 25 degrees Celsius. Different breeding pairs were crossed to determine whether there
were genetic advantages which would help protect them from higher temperatures and lower pH.
One replicate was completed. To observe how reproduction and development were affected, the
percent fertilization and percent gastrula formed were analyzed.
Through the experiment, it was found that while low pH decreased normal development,
warming increased the normal development (Foo et al., 2014). The fertilization stage did not
indicate how well the gastrulae would form. It was discovered that while pH of 7.6 negatively
affected the percent gastrula formation, the increase in temperature helped alleviate negative
effects. Because P. indiana did well in warmer temperatures, they may be able to expand their
habitat range. It is encouraged to run experiments which test more than one stressor in order to
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observe how different variables will interact, and like the experiment above, it is possible that
one variable may affect another whether it counteracts the other or works in conjunction.
Descriptive Statistics:
For the regression test, the percent fertilization was the independent variable while the
percent gastrula formed was the dependent variable. Descriptive statistics were completed for
both these variables as seen in the table below. For the percent fertilized, the outlier for the lower
limit and upper limit was 5.51 and 124.15 respectively. The variance 472.59 helps to calculate
the standard deviation of 21.74. The mean of these data was 63.50. For the percent gastrula
formed, the outlier for the lower limit was 26.42 while the upper limit was 129.19. The data set
had a mean of 75.43 with a variance of 348.85 and standard deviation of 18.68.
Table 1:
% Fertilized
MIN
Q1
MEDIAN
Q3
MAX
16.67
50.00
66.67
79.66
100.00
% Gastrula Formed
20.00
64.85
78.95
90.58
100.00
For the ANOVA test, percent gastrula formation was compared between three different
pH values: 8.1, 7.8, and 7.6, and the descriptive statistics are shown in the table on the next page.
For the chi-square test, the continuous percent gastrula formation variable was changed to a
categorical variable by determining the mean of the percentages under 22 degree Celsius
temperature and the 25 degree Celsius temperature which was 75.43 and 70.64. Anything below
these values were counted as “low” gastrula formation, while everything above these values were
“high” gastrula formation. For 22 degrees Celsius 47.92% low, while for 25 degree Celsius,
39.59% were low.
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Table 2:
pH value
Minimum
Q1
Median
Q3
Maximum
Mean
Lower Fence
Upper Fence
Variance
Standard Deviation
8.1
20.00
64.85
78.95
90.58
100.00
75.43
26.24
129.19
348.84
18.68
7.8
39.29
66.67
76.84
89.16
100.00
93.75
28.06
127.76
281.89
16.79
7.6
0.00
0.00
0.00
0.00
5.00
0.43
-38.61
38.61
1.37
1.17
Statistical Tests:
Does the pH level have a relationship with the percent gastrula formation?
In order to see whether 3 levels of pH showed any statistical differences in population
means of percent gastrula formation, an ANOVA test was run. The ANOVA test used the
independent category which were different pH levels of 8.1, 7.8, and 7.6, and a continuous
dependent category which was the percent gastrula formation, and determined whether each
level of pH showed significant statistical difference in the population means of the percent
gastrula formation.
The null hypothesis indicated that the pH levels would not have a statistically significant
difference in mean population of percent gastrula formation. The alternative hypothesis stated
that at different pH levels, there would be a statistically significant difference in the population
mean of percent gastrula formation. The calculated p-value (3.25E-60) was much lower than the
alpha (0.05), which indicated that there was a significant statistical difference in population mean
of percent gastrula formation depending on the experimental pH.
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Table 3:
Anova: Single Factor
SUMMARY
Groups
8.1
7.8
7.6
Count
48
48
48
Sum
3620.72
3572.196
20.46733
Average
75.43167
74.42074
0.426403
Variance
348.8385
281.8882
1.371715
ANOVA
Source of Variation
Between Groups
Within Groups
SS
177631.6
29708.62
df
MS
88815.79
210.6995
F
P-value
421.5283 3.25E-60
Total
207340.2
2
141
F crit
3.060292
143
To determine what caused the significance, t-tests were run between 8.1 and 7.8, 8.1 and
7.6, and lastly 7.8 and 7.6. The null hypothesis was regardless of pH values, there would be no
statistical difference in mean population of percent gastrula formation. The alternative hypothesis
indicated that the pH value would have a significant statistical difference in mean populations of
percent gastrula formation. When running a t-test between 8.1 and 7.8 pH, the p-value (0.78) was
larger than the alpha (0.05) which means that the null hypothesis was not rejected and therefore
these two pH values do not show a statistical difference in mean population of percent gastrula
formation. However, when 8.1 and 7.6, then 7.8 and 7.6 pH values were run in two other t-tests,
the p-values (4.31E-47, and 1.70E-50 respectively) were both smaller than the alpha (0.05)
which meant the null hypothesis was rejected and the lower pH value did have a statistically
significant difference between the percent gastrula formation.
The graph on the next page demonstrates how large the difference between the sample
means of different pH values was. When 8.1 or 7.8 pH was run against 7.6 pH, there were
statistically significant difference in mean population of percent gastrula formation because the
percent gastrula formation was almost non-existent in the pH value of 7.6. The population means
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of percent gastrula formation was significantly different between 8.1 and 7.6, but also between
7.8 and 7.6, therefore, the null hypothesis was rejected and the alternative hypothesis was
supported. This graph demonstrates how large the difference in mean populations really was.
Figure 1:
Average Gastrulation with pH changes
Average Gastrula Formation (%)
80.00
70.00
60.00
50.00
40.00
30.00
20.00
10.00
0.00
8.1
7.8
Experimental pH Levels
7.6
Is there a linear relationship between percent fertilization and percent gastrula formation?
To run a regression test of the percent fertilization on the percent gastrula formed, a
correlation test was first run. The correlation value (r = 0.72) indicated the two variables had a
strong, positive correlation. After the correlation value was determined, the regression was run.
The null hypothesis was the percent fertilization and the percent gastrula formed do not have a
linear relationship. The alternative hypothesis stated that the percent fertilization and the percent
gastrula formed did have a linear relationship. The regression model found had a significant pvalue (8.99E-09) which was less than alpha (0.05) indicating the null hypothesis was rejected
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and that there is a statistically significant linear relationship between the percent fertilization and
the percent gastrula formed. The graph below shows the regression line and the raw data points.
The regression line of y = 0.6172x + 36.241 demonstrated that every time percent fertilization
increases by one percent, the percent gastrula formation increases 0.617 percent. However, the yintercept did not make sense because in order for gastrula to form, fertilization needed to occur
in the first place. The r2 value (0.52) indicates that 52% of the response variable was explained
by the regression line.
Figure 2:
% Fertilization and % Normal Gastrula
120.00
y = 0.6172x + 36.241
Gastrula (%)
100.00
80.00
60.00
40.00
20.00
0.00
0.00
20.00
40.00
60.00
80.00
Fertilised (%)
100.00
120.00
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Is there a significant difference of high gastrula formation given an experimental temperature
of 25 degrees Celsius or control temperature of 22 degrees Celsius?
The null hypothesis for this chi-square test was that the probability of the high gastrula
formation given the experimental temperature will be the same probability of high gastrula
formation given the control temperature. The alternative hypothesis was the probability of high
gastrula formation given the experimental temperature will have a significant difference to the
probability of high gastrula formation given the control temperature.
To make the continuous variable of percent gastrula formation into a categorical
variable, the data was split into a “high” and “low” category where anything above 75% gastrula
formation was a “high” category and anything below 75% gastrula formation was a “low”
category. A chi-square test was run to determine if there was a significant different of gastrula
formation given a control and experimental temperature, 22 degrees Celsius and 25 degrees
Celsius respectively. The calculated p-value (0.41) for the chi-test was larger than alpha (0.05)
which meant that the null hypothesis was not rejected, therefore there was no significant
difference of high gastrula formation given the control and experimental temperatures. The table
below shows the observed and expected values which were used to find the p-value (0.41).
Table 4:
observed values
Low
High
Total
expected values
Low
High
Total
p-value
Control (22)
23
24
47
Experiment (25)
19
28
47
Control (22)
21
26
47
Experiment (25)
21
26
47
0.406625755
Total
42
52
94
Total
42
52
94
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Discussion:
In conclusion, there was evidence of a linear relationship found between percent fertilization and
percent gastrula formed, lower pH was statistically different in the mean population of percent
gastrula formed, and lastly there was no significant difference of high gastrula formation given
different temperatures. A strong linear relationship between reproduction and fertilization is
important because every percent the fertilization increases, the percent gastrula formed increases
by 0.67 percent. Secondly, there is strong evidence which shows that low pH does in fact change
the population means of percent gastrula formation. Finally, temperature does not show a
significant difference in high gastrula formation. Through the use of ANOVA, t-tests, regression
models, and chi-square tests, we are able to have a closer and more accurate interpretation of
what may happen to P. indiana in the next eighty years.
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Citations
Byrne, M., Ho, M., Selvakumaraswamy, P., Nguyen, H.D., Dworjanyn, S.A., and Davis, A.R.
(2009). Temperature, but not pH, compromises sea urchin fertilization and early
development under near-future climate change scenarios. Proc. R. Soc. London. Ser. B
Biol. Sci. 276, 1883–1888.
Foo, S.A., Dworjanyn, S.A., Khatkar, M.S., Poore, A.G.B., and Byrne, M. (2014). Increased
temperature, but not acidification, enhances fertilization and development in a tropical
urchin: Potential for adaptation to a tropicalized eastern Australia. Evol. Appl. 7, 1226–
1237.