Vick 1
Ginna Vick
Dr. Teymuroglu
BIO 342
27 November 2016
The Effects of Anthropogenic Events OnPseudoboletiaindiana
“On my honor, I have not given, nor received,
nor witnessed any unauthorized assistance on this work.”
Abstract:
To further understand how climate change and dropping levels of pH will affect marine species, an experiment on an urchin species Pseudoboletiaindiana 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. indianato 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, Pseudoboletiaindiana 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 thathigh 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).
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°Cwas 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 wellP.indianawould adapt to anthropomorphic changes in the ocean, an experiment of three pH levels, two temperatures, and different male and female crosses was completed. The experimenthad three different pH levels of 8.1, also known as the ambient pH, 7.8, and 7.6. There weretwo 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. indianadid 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 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 / % Gastrula FormedMIN / 16.67 / 20.00
Q1 / 50.00 / 64.85
MEDIAN / 66.67 / 78.95
Q3 / 79.66 / 90.58
MAX / 100.00 / 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.
Table 2:
pH value / 8.1 / 7.8 / 7.6Minimum / 20.00 / 39.29 / 0.00
Q1 / 64.85 / 66.67 / 0.00
Median / 78.95 / 76.84 / 0.00
Q3 / 90.58 / 89.16 / 0.00
Maximum / 100.00 / 100.00 / 5.00
Mean / 75.43 / 93.75 / 0.43
Lower Fence / 26.24 / 28.06 / -38.61
Upper Fence / 129.19 / 127.76 / 38.61
Variance / 348.84 / 281.89 / 1.37
Standard Deviation / 18.68 / 16.79 / 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 usedthe 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.
Table 3:
Anova: Single FactorSUMMARY
Groups / Count / Sum / Average / Variance
8.1 / 48 / 3620.72 / 75.43167 / 348.8385
7.8 / 48 / 3572.196 / 74.42074 / 281.8882
7.6 / 48 / 20.46733 / 0.426403 / 1.371715
ANOVA
Source of Variation / SS / df / MS / F / P-value / F crit
Between Groups / 177631.6 / 2 / 88815.79 / 421.5283 / 3.25E-60 / 3.060292
Within Groups / 29708.62 / 141 / 210.6995
Total / 207340.2 / 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 graphon 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 werestatistically significantdifference 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
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:
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) indicatedthe 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 p-value (8.99E-09) which was less than alpha (0.05) indicating the null hypothesis was rejected 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 y-intercept did not make sense because in order for gastrula to form, fertilization needed to occur in the first place.The r2value (0.52) indicates that 52% of the response variable was explained by the regression line.
Figure 2:
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 thatthe 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 valuesControl (22) / Experiment (25) / Total
Low / 23 / 19 / 42
High / 24 / 28 / 52
Total / 47 / 47 / 94
expected values
Control (22) / Experiment (25) / Total
Low / 21 / 21 / 42
High / 26 / 26 / 52
Total / 47 / 47 / 94
p-value / 0.406625755
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 toP. indiana in the next eighty years.
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.