Avoidance behaviors displayed by Apple Snail Pomacea diffusa in the presence of two different predators
Josh Stevens, Alana Olendorf, Doug Ericson
May 3rd, 2018
Bio 345 – Animal Behavior
Prey animals are able to respond to the presence of predators in many different ways, such as hiding, fleeing, altered movement, and many other behaviors which may show specific predator avoidance. These avoidance tactics vary among species and this study focuses on predator avoidance tactics used by freshwater snails Pomacea diffusa. We hypothesized that Apple snails, Pomacea diffusa, show predator specific avoidance behavior behavior as a response to chemical signals from predators. This experiment was done in two parts with two different predators. There was a separate control for each experiment which consisted of only the enclosure that the predator would be held in. We also did 6 additional trials for each of the two separate experiments. In the first experiment a crayfish was used as the predator and in the second experiment a Betta fish was used. Our results from the first experiment showed that that there was a statistically significant difference in the amount of snails that were in low locations in the tank versus the amount of snails that were found in high locations when the crayfish was introduced.There was not a statistically significant difference in the snails location when the Betta fish was introduced. While the data collected provides some support specific responses to a predator, further studies are necessary to fully explain the specific avoidance behaviors displayed by freshwater snails in response to predators.
Predator-prey interaction is, in essence, the ongoing genetic battle to overcome the opposition (Dawkins & Krebs, 1979). As one party adapts to effectively interact with the other party, the other must also adapt to account for the change. As a predator population becomes more adapted to hunting the prey species, the prey population will also adapt in response to the selection pressure generated by the predator adaptation (Corcoran and Conner, 2017). These adaptations can come in the form of morphological, physiological, and/or behavioral changes. For the predator these changes could involve adaptations in the ability to find prey, and eat prey. For prey species, these adaptations could involve detecting and avoiding predators.
Predator detection has enormous selection pressure as compared to prey detection pressures due to the Life-Dinner Principle (Dawkins & Krebs, 1979). There are many ways that predators and prey detect one another; sight, sound, touch, smells, chemical cues, etc. The ability of predators or prey to detect the other party can be selected for sensitivity, specificity, and/or adaptability. Specificity as in the ability to differentiate between predators or prey (Aizaki & Yusa, 2009). Sensitivity as in the ability to detect signals at low intensities (Levri et al., 2017).
The ability to detect chemical cues from predators can be very important tools for prey species. For some species that live in the dark, or are hiding, it can be the only cue available.This ability allows the prey to have information on the risk of predation at a certain place and time. The prey are able to detect what predators are currently present or have been there very recently. In some cases, it is also able to reveal the predators activity level and diet (Kats & Dill, 1998). Even though in many cases it is the predator giving off chemical cues, sometimes it is the prey giving them off. These cues can be released when they detect or get attacked by a predator and are referred to as chemical alarm systems. The other prey individuals that pick up these chemical alarm systems are less vulnerable to predation (Chivers & Smith).
When a predator is detected, snails will alter their behavior in order to avoid the predator. Snails can exhibit a variety of different avoidance behaviors such as climbing, burrowing and hiding (Armajo and Sura, 2012). The avoidance tactic used can vary depending on what species of predator is present. Snails use chemical cues in the water to detect predators. Each predator gives off a different chemical cue which can allow snails to display appropriate avoidance behaviors (Levri et al., 2017). Chemical signals from turtles tend to make snails bury themselves, however chemical signals from fish will usually cause snails to try to get above the water line (Ueshima, Yusa, 2015). Snails can also “learn” avoidance behaviors if they are conditioned to certain predators as hatchlings. Hatchlings conditioned to a certain species of predator exhibit much higher alarm response when exposed to the same type of predator than when introduced to a new predator (Aizaki and Yusa, 2009) . Another species of pulmonate snails, Physella virgata, shows a avoidance behavior specific to the crayfish species, Procambarus simulans (Alexander & Covich, 1991).
The goal for this experiment was to determine what predator avoidance behavior Mystery snails display in the presence of Betta fish and crayfish kairomones. Specifically, we want to determine if the snails display different avoidance behaviors depending on the type of predator present. We hypothesized that Apple snails, Pomacea diffusa, show predator specific avoidance behavior behavior as a response to chemical signals from predators. Specifically, if the crayfish is introduced, then the snails will go above the water line and if the betta fish is introduced, then the snails will try to be low in the tank or hide under the flower pot.
Freshwater Apple snails, Pomacea diffusa were used in this experiment. Apple snails are a species of freshwater gastropods. Freshwater gastropods can be found on every continent except for Antarctica. They can also be found in almost any freshwater habitat including lakes, streams, ponds and rivers (Strong, 2008) . Apple snails are the largest species out of all freshwater gastropods, their shell can get up to 145 mm tall (Burky, 1974).
Housing and Care
Freshwater Apple snails were obtained from the Carolina Biological Supply. They were kept in a filtered 10 gallon fish tank while they were not being used for an experiment. All of the snails were moved to a different tank when they were being used for an experiment, but were always returned to the same tank afterwards. In the tank, there was a flower pot in the corner that they could hid in and there were small rocks on the bottom of the tank. The tanks were kept on a lab bench in a Keene State College research lab. For food, two algae tablets were put into the tank every other day.
There were two apparatus’ used for this experiment. The first one consisted of a filtered 10 gallon fish tank with a metal cage in the middle of it and a flower pot in the far left corner (Fig. 1). The second apparatus consisted of a second 10 gallon fish tank with another flower pot in the far left corner and a net in the middle of the tank (Fig. 2).
Figure 1. Experimental apparatus. This is a front view of the apparatus. It consists of a 10 gallon fish tank with a cage in the center and a flower pot in the far left corner.
Figure 2. Experimental apparatus. This is a front view of the apparatus. It consists of a 10 gallon fish tank with a net in the center and a flower pot in the far left corner.
Our experiment consisted of two parts. Both parts of the experiment were done in the same way, but the predator being used differed. Before any data was collected in either part of the experiment, all 6 of the snails were placed into the appropriate test tank and given at least one hour to acclimate to the new tank. After data was collected, all of the snails were moved back to their “home” tank. We used the same control in both experiments. The control used was observing all 6 of the snails in the crayfish test tank with only the flower pot in it for 30 minutes. We recorded where the snails were in the tank every 3 minutes during this time period. We did this on three different days. These tests were done before the crayfish had been introduced into the water so the water did not have any chemical cues from that in it. All of the tanks were kept at the same temperature with the same pH.
The first part of experiment 1 was to observe all 6 of the snails in the crayfish test tank with only the cage in it. We recorded where each of the snails were in the tank every 3 minutes for a 30 minute time period. This was done to make sure that the metal cage was not altering the snails behavior. We did this test a total of 3 times, all on different days and different times. The last step in the first experiment was to put one crayfish in the cage and record where the snails are in the tank every 3 minutes for a 30 minute time period. Three of these tests were done on different days at different times.
Experiment two was done by first observing all 6 of the snails in the betta fish test tank with nothing but the flower pot and the net in it. The snails were recorded every 3 minutes for a thirty minute time period on three separate days. The next step was to introduce the betta fish. The snails were observed in the test tank with the betta fish in the net and their position was recorded every 3 minutes for a 30 minute time period. There were three of these tests done on different days at different times.
A one-way ANOVA test and post-hoc Tukey HSD was used to determine if there was a statistically significant difference in the mean number of snails found in the expected location (high or low) for treatments with a predator present, a container present, and a control . The locations were separated into two category locations high, which included on the wall, top of wall, and on the pot, and low, which consisted of on the ground, in the pot, and snail on snail. The results from the three tests of the 5 separate tests (no variable, cage only, net only, crayfish, betta fish) were summed to give the high and low locations over the 90 minute span each test ran for. The mean of the high and low locations were determined for each of the test variables and compared using a one-way ANOVA with post-hoc Tukey HSD test to determine if our data showed significant difference.
We did two separate experiments. Each part included a separate control treatment which included only the enclosure the predator was being held in. The initial control treatment, enclosure control treatment, and predator introduction phase.
We found that the mean number of snails in a high location increased significantly when the crayfish was introduced (Fig. 3.). The mean number of snails that were in a high location when the crayfish was introduced was compared to the control treatment (Tukey HSD: Q statistic = 12.55, P = 0.00101; Fig 3). The introduction of the cage also showed significantly different data compared to the control and the introduction of the crayfish (Tukey HSD: Q statistic = 7.34, P = 0.001005) and (Tukey HSD: Q statistic = 5.37, P = 0.001912), respectively.
Figure 3. The mean, per 3 minute interval, number of snails located in a high location with no variable present, only the cage present, and the crayfish and cage present. The difference in high location was significantly different with the introduction of the crayfish when compared to the control treatment (Tukey HSD: Q = 12.711, P = 0.00101). Error bars are standard error.
We found that the mean number of snails in a low location remained the same as the control when the betta fish was introduced (Fig. 4). The statistical analysis showed that there was no significant difference from the control treatment when compared with the introduction of the betta fish (Tukey HSD: Q = 0.00, P = 0.900; Fig 4).
Figure 4. The mean, per 3 minute interval, number of snails in a low location with the no variable present, only net present, and net with betta fish present. The difference in low location was not significantly different with the introduction of the betta fish when compared to the control treatment (Tukey HSD: Q = 0.00, P = 0.900).
Comparison of Experiments
We found that the mean number of snails in either a low location or a high location was different when the crayfish was introduced compared to the introduction of the betta fish (Fig.5). The difference in low location and high location was significantly different between the two predator introductions (Tukey HSD Q = 12.6, P = 0.001) (Tukey HSD: Q = 12.5, P = 0.001), respectively.
Figure 5. The mean, per 3 minute interval, number of snails in a low (left) and high (right) locations with the introduction of the crayfish and betta fish. There was a significant difference in mean amount of snails in both the low and high locations with the low location (Tukey HSD Q = 12.6, P = 0.001) and high location (Tukey HSD: Q = 12.5, P = 0.001).
This experiment provided evidence that the presence of crayfish in the snails environment altered the snails behavior. We hypothesized that Apple snails, Pomacea diffusa, show predator specific avoidance behavior behavior as a response to chemical signals from predators. Our results from the first experiment supported our hypothesis while the results from the second experiment did not support our hypothesis. From the results, we concluded that the presence of the cage did have an influence on whether or not the snails would be found low in the tank. In the net experiment, on the other hand, the presence of the net had no effect on where the snails were found in the tank. The same results were found in reference to snails found high in the tank. The disparity between the two tests may be attributed to differences in: location of the container in the tank, materials making up the container, and the snails ability to sense the presence of the container. Other experiments did not use caged predators, but rather water that had a predator in it for some time (Ueshima, Yusa, 2015) and (Dalesman et al. 2007). In our preliminary experiment of using “predator water” the snails did not elicit a response to the introduction of the water, so our experiment had to be changed. Additionally, we used snails purchased from Carolina Biological Supply.
The data from the predator and the container vs. nothing suggests that with the addition of the crayfish and the cage there was a statistically significant difference in where the snails were found, low or high in the tank. These results are similar to another study that used crayfish as a predator with P.virgata, and P. trivolvis snails. Their results showed that when a crayfish was introduced, the snails crawled up above the water line (Alexander & Covich). For the betta test, there was no difference between the presence of the betta fish and the absence of it. It appears that the snails may not have been able to sense the betta, or they could and they did not change their behavior because of it. For the crayfish it seems that they could sense the crayfish, and the cage. In a study comparing the response to predator cues of two snail species, Bellayma chinensis and Heliosoma trivolvis, found that the response of B. chinensis was significantly less responsive to the cues compared to the other species (Armajo and Sura, 2012).
The data that compares the snails behavior with the predator and just the cage suggests that the response of the snails was statistically significantly different between presence of the cage and the presence of the crayfish in the cage. This confirms that the cage itself was not the sole cause of the behavior change in the snails. For the betta fish and the net there was not a statistically significant difference in the snail behavior. In the (Armajo and Sura, 2012) experiments, they too put their predators in a container (a mesh net), but they did not test to see if its presence had an effect on the behavior of the snails.
The statistical test confirms that the snails did exhibit a different response to the different treatments. This result was also found in the (Armajo and Sura, 2012) experiments looking at climbing and burrowing behavior. From the previous tests we know that the snails did respond to the crayfish and the crayfish cage while they did not respond to the betta fish and the betta fish net. This is the result we would expect for a test between a predator and a non-predator. This could mean that the snails did not recognize the betta fish as a predator, or the snails could not detect the betta fish. Some snail species, usually invasive species, have the ability to detect and respond to unfamiliar predators. In a study researching Potamopyrgus antipodarum and their variance in behavioral responses to predator cues (Levri et al., 2017).
In a study that tested Antipredator behaviour in response to a common carp, a Reeves turtle and combined predator cues in the apple snail Pomacea canaliculata, it was shown that the snails responded more to the odour of the crushed conspecifics than to the carp or the turtle odours (Ueshima, Yusa, 2015). This was also shown in another study that tested predator response in the freshwater gastropod Lymnaea stagnalis (Dalesman et al. 2007), which suggests that the perceived risk of the predator cue alone is not enough for the snails to exhibit an avoidance response. This could be due to the energetic cost of the response and other risks involved with the response. The energetic cost must outway the risk of predation if only a predator cue is present.
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