"Oh Jesus Bugs"

This topic submitted by Alisha Weis, Kathryn Bertram, Jennifer Kelleher, Brian Crosby, Tim Skinner ( crosbybj@miamioh.edu ) on 12/10/98 .

Kathryn Bertram, Jennifer Kelleher
Brian Crosby, Tim Skinner and Alisha Weis
Natural Systems 1
Hays Cummins
December 11, 1998


Water Striders, "Oh Jesus Bugs"

INTRODUCTION:
Our goal is to study and compare the abundance and characteristics of water striders found in different sections of the creek on Western Campus and in the creek of Pfeffer Park. In doing this experiment we want to find out if changes in the environment will have any effects on the characteristics and/or the abundance of water striders. To find this we will compare four pools of water with different current rates and depths. Two of these sections will be kept similar so that we can see if similar environments will have consistent results. We will measure the lengths and weights of the striders and approximate their abundance in each pool. We will then try to decide if the environments have any significant effects on our data. Throughout our discovery lab we plan to accomplish several experiments. First of all we will test the effects that different water currents and depths have on the lengths, weights, and abundance of water striders. Second, we will compare lengths, weights, and abundance of striders from similar areas of the two different creeks. Last, we will choose a section from the western creek and re-test their length, weight, and abundance after the air temperature has dropped below 32 degrees Fahrenheit. We will compare these results to our original results to see if a change in weather has an effect on the striders.
From our initial observations, we made the prediction that water striders would have an average weight of .04 grams and have a length between 10 and 11 millimeters. Striders would be found in slow moving pools of water throughout the creeks, and would also water striders live in groups of twenty to thirty. This led us to form the hypothesis that water striders are more abundant in deeper and slower current areas of water. Also, in general the mass and lengths of water striders will not be significantly effected by their environmental conditions.
There are many reasons why the study of water striders is relevant. First of all, water striders are an important part of the water system. They are also interesting to study because many people do not research bugs, none the less, water striders. When a person is asked, "What is a water strider?" one can only reply with a questionable look on their face. Therefore, we thought that it would be intriguing to pursue a subject that is not very well known.
Hypothesis:
Water striders are more abundant in deeper and slower current rates of water. Also, in general the mass and lengths of water striders will not be significantly effected by their environmental conditions.
Questions:
* Where do water striders live?
* Are there significant differences in their characteristics such as length and weight?
* Are there variations in the amount of striders in other sections of the stream and or different environments?
* Will there be a different abundance in dissimilar weather conditions?
* Do they prefer sunlight or shade?

RELEVANCE OF YOUR RESEARCH QUESTION:
In the past, other researchers have focused on several subjects relating to water striders. First of all, mating and its risks have been a major study. In addition, researchers have included studies of water striders defending their territory, how they walk on water, their behaviors, their characteristics, and their evolution. However, on a larger scale, the bigger question is in fact, "How do water striders contribute and fit into the environment?" The answer to this question has several parts. The food chain has much relevance. Small fish eat water striders and water striders also eat insects that are smaller than them, therefore contributing to the recycling system of the food chain. Everything in the environment serves a purpose and without the presence of water striders, how would the earth survive? Moreover, this has a greater application to the survival of the aquatic ecosystem. This question in fact is hypothetical, for it does not have a true answer.
In our lab we chose to study the abundance and characteristics of water striders. Through our research we discovered that there has been a lab done pertaining to the characteristics and abundance of water striders. According to a group at Lake Forest College who studied water striders, the water striders tend to live in communities of fifteen to forty individuals. They also came to the conclusion that water striders reside in locations with slower current rates for the purpose of energy conservation. These are two traits that we, in our lab group plan to identify. The hypothesis for this lab done by the Lake Forest College was: "Water strider size is indirectly proportional to water current rates" (http://www.ifc.edu/biology/houde/waterstriders/intro.html). This hypothesis relates to our lab in that we will be looking at water currents and the effects it may have on the sizes of water striders. We are also studying the abundance of striders, as did Lake Forest College.

OTHER STUDIES IN RESEARCH:
"The Costs of Mating and Mate Choice in Water Striders." Rowe, Locke Animal Behaviour, p. 1049-1056. Nov. 1994.

This article explained results found in a study of the mating behavior of water striders, and the risks involved with mating. There were four mating behaviors described. First, males frequently search for females. Second, there are pre-mating struggles in which the female tries to escape the male's search. Third, there is the actual mating in which the male guards the female. Last there is the post-mating struggle.
It was found that predation risks are increased when the water strider is mating. In fact, the predation of mating females was three times that of single females. Though there was no significant increase in the predation of males, it was found that some of the males' mating behaviors can be very dangerous. During mating season, males spend more time in open waters and move more often even than females. This causes an attraction to the backswimmer, the water strider's most common predator. Because water striders usually take refuge on floating debris in the water, the backswimmer has a higher capture rate of mating water striders that move around more often.


"Sexual Selection and the Evolution of Sexual Size Dimorphism in the Water Strider, Aquarius Remigis." Fairbarin, Daphne J, Preziosi, Richard F. Evolution p. 1549-1559 Aug. 1996.

This article explained how selection through mating could be related to the evolution of the water strider. It explained that sexual selection actually occurs through female reluctance towards the male, rather than the female choice. Typically, selection is based on the size of the male. This article described a study done on this subject. It was found that the selection is slightly based on the wing forms of the male water strider, and that larger males are favored for selection. Both males and females mate repeatedly during the mating season, which runs from spring to early summer. If the male harassment rates are high, then the selection of females is lower, which therefore reduces the risks involved with mating.

"Fitness Consequences of Food-based Territoriality in Water Striders, Gerris Remigis." Blackenhorn, Wolf U. Animal Behaviour p. 147-149. 1991.

This article described how water striders defend their territories. The general size of the water strider's territory is about 30 to 40 centimeters in diameter. Water striders are generally surface sit-and-wait predators. The more dominant water striders are more aggressive, and have a higher body mass gain before winter hibernation. There is a high mortality rate of water striders in the winter because the less dominant ones tend to die off, and because mating is delayed until the spring, so there is no chance for new life.

"Multiple Mating in a Water Strider: Mutual Benefits or Intersexual Conflict?" Arnqvist, Goran Animal Behaviour p. 749-755. 1989.

The question asked in this article is: why do female water striders mate multiple times? There is really no obvious reason for this because a female should be able to go ten days without being around males while sustaining a normal egg production rate. Through this study, Arnquist decided that by mating, striders multiply and also avoid the male's search process. Females are in high risk for predation during mating since they tend to move around more. This attracts the predator, the backswimmer. However, if the female goes too long without being surrounded by males, she will die sooner than one who is surrounded by males. So really, either way there is a risk for the female. Mating multiply actually is beneficial to the male because it increases the reproductive success.

"Heritability and Repeatability of Behavioural Attributes Affecting Foraging Success and Fitness in Water Striders." Blanckenhorn, Wolf U, Perner, Dirk. Animal Behaviour p. 169-176. 1994.

This article deals with characteristics of water striders. It tries to figure out if the characteristics are genetic or through adaptation. The study done for this experiment was not very successful. It was found that capture accuracy was different for many of the water striders because it is influenced by hunger. It was also found that skittishness and aggressiveness were probably more genetic characteristics.

MATERIALS AND METHODS:
Process in doing this lab:
1-Get a net to catch insects with, along with several small plastic containers.
2-Go to Pfeffer Park and go to the section of the creek that has the two tracks running through it.
3- Go to the edge of the creek and collect twenty water striders. You will be able to identify a water strider by the following characteristics: six legs, walking/ hopping on top of the water, about three quarters of an inch long, dark gray, skinny and very fast moving.
4- Label the container "Pfeffer Park".
5- Record observations including: water current, relative depth, sunny or shady and abundance.
6- Head over to the creek on Western Campus.
7- Go to the mouth of the creek where there is a slow moving pool of water.
8- Follow steps 3 through 5, but label this container "Mouth of creek"
9- Go to the first bridge and follow steps 3 through 5. Label one container North Side and one South Side and repeat steps 3-5 for both sides of the bridge.
10- Go to the bottom of the hill by McKee Hall. Once there go to the creek that is in the woods about fifty feet. Then label the container "McKee Hall"
11- Follow steps 3 through 5.
12- Go to Boyd Hall and go to the Science Center.
13- Get a pair of Vernier Calipers and an electric scale.
14- Weigh the striders to one hundredth of a gram and measure to the nearest millimeter. Record all data collected.
15- Return all the striders to the areas they were collected.

When involving the rest of the class in our study, we had them weigh and measure the water striders that we had previously frozen .We will taught the class how to operate the equipment that we have used throughout our lab. These instruments would include calipers and a digital scale. Furthermore, we provided the class with two sets of data that we have previously gathered so that they will be able to compare and contrast our data with their own. From this data, the class was able to draw some of the same conclusions about water striders that we will have in our lab. A worksheet was distributed to the class explaining the step by step instructions.
We made a brief video tape of water striders in their natural environment. It shows striders moving about the water and how they chose to stay in groups. Although there is not a plethora of water striders in the video, there is one part where two striders join each other, showing that they like to follow one another.

TIMELINE:

Week 1 (8/30- 9/6): Decided to study water striders
Week 2 (9/7-9/13): Researched multiple texts at King Library and posted our research idea on the Internet.
Week 3 (9/14-9/20): Posted a progress report on the web describing our procedure.
Week 4 (9/21-9/27): Collected water striders, weighed them, measured them and wrote our open inquiry lab, and made observations.
Week 5 (9/29-10/4): Went to the pond and creeks again and gathered samples of water striders and we also took pictures, weighed them, measured them and made observations again.
Week 6 (10/5-10/11): Collected more water striders, video taped them, weighed them, measured them and observed them.
Week 7 (10/12-10/18): Met with Hays and discussed our lab in depth. We also worked on our research proposal.
Week 8 (10/19-10/25): Collected more water striders in Pfeffer Park and on Western campus. We weighed and measured them. We also did our lab packet! How fun!
Week 9 (10/26-11/1): We will collect, weigh and measure water striders again before it freezes. Furthermore we will add more observations.
Week 10 (11/2- 11/8): Work on statistics and final preparation for lab project and presentation.
Week 11 (11/9-11/15): Present our fabulous water strider lab to our highly intelligent Natural Systems class!
December: Present final presentation to the class and work on our final paper and statistics.

RESULTS: (NOT WIDE ENOUGH)


South Side (frozen) North Side PondMouth Pfeffer Park Fast Current
Current Very Slow Slow Very Slow Slow Fast
Depth Deep Pool Deep Pool Average Depth Average Depth Shallow
Abundance 50-55 35-40 30-35 25-30 10-15
Light Well Shaded Well Shaded Shady Sunny Shady
Mean Weight .023g .038g .042g .044g .044g
Mean Length 12.985mm 10.265mm 13.507mm 13.825mm 13.434mm


The results of the mass of water striders are as follows; the mean was .037 grams, and the standard deviation was .012. The results for the lengths of water striders are as follows; the mean was 12.732 millimeters, and the standard deviation was 2.046.
As well as these statistics, we have made general observations of the water striders that are in agreement with our hypothesis. We've found that water striders tend to be more abundant in slower moving pools of the stream and that they form large groups beneath overhangs. They also seem to prefer shaded areas. We have found that water striders do not come back after their season is over. This happens after the first frost of the year. Because of this fact we were unable to carry out one of our tests that was stated in our introduction, to test the weight, length, and abundance after the temperature went below 32 degrees Fahrenheit. Striders also are not abundant when it rains. They seek protection from the bad weather. While observing the different traits of water striders, we have found that some of them have white bellies and others have silver bellies. The striders with white bellies are smaller in size than the others. This leads us to believe that they are from different species.
There are several reasons why we did the tests that we did. First of all, we performed the ANOVA test, which determined our p- value. It told us that the p-value was less than .0001 meaning that there was a significant difference in our data somewhere. The second test, the Scheffe, actually told us where the significant differences in our data were. For the Scheffe for length the p-value was less than .0001 when the north side was compared to each of the four other sections. When the Scheffe was performed for weight the p-value was less than .0001 each time that the south side was compared to the four other sections.

DISCUSSION AND CONCLUSION
Our hypothesis for this lab was that water striders are more abundant in deeper and slower current rates of water. Also, the mass and lengths of striders will not be significantly effected by environmental conditions. We found both parts of our hypothesis to be true. From observations that we have made, the striders were more abundant in areas of slower current rates and in deeper areas. The means of their lengths and weights were also similar between the different sections, showing that relative depth and current rates do not have a significant effect.
In addition to proving our hypothesis, we were also able to answer questions concerning conditions other than the depth and current rates of the stream. Through observation, we were able to conclude that the striders are not abundant during rain. They seek shelter during rainstorms underneath the bank's edge or under leaves upon the shore. We believe they do this because they must be protective of their hair follicles, due to the knowledge that they will die if their hairs get too wet. Hence, they WALK on water! We were also able to observe the water strider's reaction to the cold weather. After going to the stream after the weather was consistently cold the abundance of the striders had gone way down and by the end of November there were no striders left. This is because they go into hibernation in the winter. We were unable to make a definite conclusion as to whether or not striders prefer shade or sunlight. We only had one section with a lot of sunlight. In order to get justifiable results we should have had more than one section in the shade and more than one section in the sun so they could be compared equally.
Our null hypothesis for this lab states that there will be no significant differences in the data compared between each section. After interpreting the t-test (p-value) we were able to accept this hypothesis for most of the sections. Exceptions to this were the weight of the south side striders and the length of the north side striders. The p-value for the lengths of the north side striders versus the other sections was less than .001 therefore we must reject the null hypothesis. We are unsure why this difference occurred because there are no environmental conditions that should have effected this data. The p-value for the weights of the south side striders versus the other sections was also less than .001 again causing us to reject the null hypothesis. These were the stiders that we used in our presentation to the class, and had been frozen before hand. We believe that the freezing caused the striders to lose a significant amount of weight.
When compared to previous research done on water striders, we have had similar results. The group at Lake Forest College mentioned earlier in our lab found that water striders tend to live in groups of fifteen to forty. We found the range of abundance in the creek on western campus to be ten to fifty five. Our research also tells us that the water striders are more abundant in areas with slower current rates. We also found this to be true in our lab.
We have thought of many other questions and experiments that could have made our lab better if we were to do a further investigation. As mentioned before, we found that the water striders go into hibernation for the winter. The larger striders usually survive the long winters while the smaller, weaker striders die off. Because of this, we believe that the population of striders would change drastically from fall to spring. There would be a lower abundance in the spring, but most of the striders would be larger making the mean lengths and weights higher than our results from this lab. We may also have wanted to observe the mating of the water striders, which takes place in the late spring. We found in the lab that some of the striders had white bellies while others had brown. We came to the conclusion that this was because they were of different species. It would have possibly been interesting to study different species of striders. We were unable to distinguish male striders from female striders. It would have been interesting to compare the abundance of each of these in each section. We could have also benefited from having more test sites within the two creeks along with testing different creeks in the area. By having more diverse sections as well as more similar sections, we would have been able to make more comparisons between environments and perhaps gotten more specific results.

BIBLIOGRAPHY:
Berenbaum, May R. "Insects and Their Impact On Human Affairs."
Addison- Wesley Publishing, New York, 1995.

Gillott, Cedric. Entomology, Second Edition, Plenum Press, New York, 1995.

Martin, Patricia A. Fink. "Animals That Walk On Water." Grolier Publishing, New York, 1997.

Nuridsanu, Claude, "Microcosmos, The Invisible World Of Insects"
Anderson Publishing, New York, 1993.

O' Toole, Christopher. The Encyclopedia Of Insects, Facts On File Publishing, Inc. New York, 1987, '89, '93.

"Sexual Selection and the Evolution of Sexual Size Dimorphism in the Water Strider,Aquarius Remigis." Fairbarin, Daphne J, Preziosi, Richard F. 'Evolution' p. 1549-1559 Aug. 1996.

"The Costs of Mating and Mate Choice in Water Striders." Rowe, Locke 'Animal Behavior,' p 1049-1056 Nov. 1994.

"Fitness Consequences of Food- based Territoriality in Water Striders, Gerris Remigis." Blackenhorn, Wolf. U. Animal Behavior p. 147- 149. 1991.

"Multiple Mating in a Water Strider: Mutual Bennefits or Intersexual Conflict?" Arqvist, Goran Animal Behaviour p. 749- 755. 1989.

"Heritability and Repeatability of Behavioural Attributes Affecting Foraging Success and Fitness in Water Striders." Blackenhorn, Wolf U, Perner, Dirk. Animal Behaviour p. 169-176. 1994

Water Strider Lab Worksheet

Objective: In this lab you will be measuring and weighing water striders. You will compare the data you find to data you are given. The data you are given will be from a separate section of the creek than the water striders you will be studying. The purpose is to conclude whether or not the environment has an effect on the characteristics of the water striders.

Materials: Calipers
Digital scale
Frozen water striders
Net
Plastic container

Procedure:
A. Groups: The class will be divided into four groups. Each group is given five frozen water striders to test. Two groups will be working on the scales and two groups will be working with the calipers.
B. Using the digital scale: Make sure that the scale is set at zero before you start. Place a water strider on the scale and record the mass to the nearest hundredth of a gram. Mass each strider separately and record in the data table.
C. Using the calipers: Adjust the calipers so that a water strider is placed between the arms. Read the measurement that is located on the side of the caliper and make sure that it is accurate to one hundredth of a millimeter.
D. After recording both the masses and lengths of the group of five striders, rotate with the other groups in the class. Continue to go through the same procedure until you have data for all twenty water striders recorded in the data sheet.
E. Going to a sight: For this part of the lab, you will be going out of class with your group to collect a sample of twenty water striders on your own. You will go to one of the four sights on the western creek and will be lead there by one of the people in the water strider lab group. Once you reach the sight record observations about the environment of the creek and about the approximate abundance of water striders. Once you have done this collect twenty water striders with the net and place each of them in the plastic container. (Please return the water striders to the creek after measuring them!) Go back to Boyd Hall and follow the procedure in the above steps.
F. Calculations: You will find the means of mass and length from each group of water striders.
G. Questions: Answer the questions and make conclusions using the data you record.

Data Sheet:
Water Strider # Mass (grams) Length (millimeters)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Environmental Observations: The western creek near the bridge is very slow moving, shady, deep and contained between fifty to fifty- five water striders.


Given Data:
Water Strider # Mass (grams) Length (millimeters)
1 .04 14.65
2 .05 13.55
3 .04 12.50
4 .06 15.55
5 .05 13.60
6 .04 14.45
7 .04 13.00
8 .04 13.05
9 .04 13.35
10 .04 13.90
11 .03 12.25
12 .05 14.15
13 .04 13.85
14 .05 14.45
15 .05 14.10
16 .04 14.45
17 .05 15.55
18 .05 14.15
19 .04 12.90
20 .03 13.05

Environmental Observations:
Slow moving current, sunny, shallow area, contained about 25-30 striders.

Data Sheet:
Water Strider # Mass (grams) Length (millimeters)
1 .04 14.90
2 .03 12.45
3 .05 14.85
4 .04 12.45
5 .06 14.40
6 .04 12.75
7 .04 13.85
8 .04 12.95
9 .04 11.65
10 .06 15.95

Environmental Observations:

fast moving current, shady, shallow area, contained 15 to 20 striders.


Questions:
Are there differences in the environments? What are they?

What is the average mass/ length of the water striders from each separate section?

Compare the average mass, length, and abundance from the three sections. Are there differences or similarities between the three sections, and if so why? You will need to perform a t-test to answer this question.


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